Archive for October 2018

What do you predict would happen if you replace the Lac operator DNA from the Lac operon with the DNA from the operator region from the tryptophan operon?

10:52

What do you predict would happen if you replace the Lac operator DNA from the Lac operon with the DNA from the operator region from the tryptophan operon?



(a) The presence of lactose will not cause allosteric changes to the Lac repressor.
(b) The Lac operon will not be transcribed when tryptophan levels are high.
(c) The lack of glucose will no longer allow CAP binding to the DNA.
(d) RNA polymerase will only bind to the Lac promoter when lactose is present.


Answer: B

Which of the following statements about the Lac operon is false?

10:52

Which of the following statements about the Lac operon is false?



(a) The Lac repressor binds when lactose is present in the cell.
(b) Even when the CAP activator is bound to DNA, if lactose is not present, the Lac operon will not be transcribed.
(c) The CAP activator can only bind DNA when it is bound to cAMP.
(d) The Lac operon only produces RNA when lactose is present and glucose is absent.


Answer: A

The tryptophan operator ________________.

10:52

The tryptophan operator ________________.



(a) is an allosteric protein.
(b) binds to the tryptophan repressor when the repressor is bound to tryptophan.
(c) is required for production of the mRNA encoded by the tryptophan operon.
(d) is important for the production of the tryptophan repressor.


Answer: B

Operons ________________.

10:51

Operons ________________.



(a) are commonly found in eukaryotic cells.
(b) are transcribed by RNA polymerase II.
(c) contain a cluster of genes transcribed as a single mRNA.
(d) can only be regulated by gene activator proteins.


Answer: C

Which of the following statements about transcriptional regulators is false?

10:51

Which of the following statements about transcriptional regulators is false?



(a) Transcriptional regulators usually interact with the sugar-phosphate backbone on the outside of the double helix to determine where to bind on the DNA helix.
(b) Transcriptional regulators will form hydrogen bonds, ionic bonds, and hydrophobic interactions with DNA.
(c) The DNA-binding motifs of transcriptional regulators usually bind in the major groove of the DNA helix.
(d) The binding of transcriptional regulators generally does not disrupt the hydrogen bonds that hold the double helix together.


Answer: A

Investigators performed nuclear transplant experiments to determine whether DNA is altered irreversibly during development. Which of the following statements about these experiments is true?

10:51

Investigators performed nuclear transplant experiments to determine whether DNA is altered irreversibly during development. Which of the following statements about these experiments is true?



(a) Because the donor nucleus is taken from an adult animal, the chromosomes from the nucleus must undergo recombination with the DNA in the egg for successful development to occur.
(b) The embryo that develops from the nuclear transplant experiment is genetically identical to the donor of the nucleus.
(c) The meiotic spindle of the egg must interact with the chromosomes of the injected nuclei for successful nuclear transplantation to occur.
(d) Although nuclear transplantation has been successful in producing embryos in some mammals with the use of foster mothers, evidence of DNA alterations during differentiation has not been obtained for plants.


Answer: B

Which of the following statements about differentiated cells is true?

10:50

Which of the following statements about differentiated cells is true?



(a) Cells of distinct types express nonoverlapping sets of transcription factors.
(b) Once a cell has differentiated, it can no longer change its gene expression.
(c) Once a cell has differentiated, it will no longer need to transcribe RNA.
(d) Some of the proteins found in differentiated cells are found in all cells of a multicellular organism.


Answer: D

The human genome encodes about 21,000 protein-coding genes. Approximately how many such genes does the typical differentiated human cell express at any one time?

10:50

The human genome encodes about 21,000 protein-coding genes. Approximately how many such genes does the typical differentiated human cell express at any one time?



(a) 21,000—all of them
(b) between 18,900 and 21,000—at least 90% of the genes
(c) between 5000 and 15,000
(d) less than 2100


Answer: C

The distinct characteristics of different cell types in a multicellular organism result mainly from the differential regulation of the ______.

10:49

The distinct characteristics of different cell types in a multicellular organism result mainly from the differential regulation of the ______.



(a) replication of specific genes.
(b) transcription of genes transcribed by RNA polymerase II.
(c) transcription of housekeeping genes.
(d) proteins that directly bind the TATA box of eukaryotic genes.


Answer: B

A neuron and a white blood cell have very different functions. For example, a neuron can receive and respond to electrical signals while a white blood cell defends the body against infection. This is because ______.

10:49

A neuron and a white blood cell have very different functions. For example, a neuron can receive and respond to electrical signals while a white blood cell defends the body against infection. This is because ______.



(a) the proteins found in a neuron are completely different from the proteins found in a white blood cell.
(b) the neuron and the white blood cell within an individual have the same genome.
(c) the neuron expresses some mRNAs that the white blood cell does not.
(d) neurons and white blood cells are differentiated cells and thus no longer need to transcribe and translate genes.


Answer: C

An extraterrestrial organism (ET) is discovered whose basic cell biology seems pretty much the same as that of terrestrial organisms except that it uses a different genetic code to translate RNA into protein. You set out to break the code by translation experiments using RNAs of known sequence and cell-free extracts of ET cells to supply the necessary protein-synthesizing machinery. In experiments using the RNAs below, the following results were obtained when the 20 possible amino acids were added either singly or in different combinations of two or three:

10:49

An extraterrestrial organism (ET) is discovered whose basic cell biology seems pretty much the same as that of terrestrial organisms except that it uses a different genetic code to translate RNA into protein. You set out to break the code by translation experiments using RNAs of known sequence and cell-free extracts of ET cells to supply the necessary protein-synthesizing machinery. In experiments using the RNAs below, the following results were obtained when the 20 possible amino acids were added either singly or in different combinations of two or three:


RNA 1: 5'-GCGCGCGCGCGCGCGCGCGCGCGCGCGC-3'
RNA 2: 5'-GCCGCCGCCGCCGCCGCCGCCGCCGCCGCC-3'

Using RNA 1, a polypeptide was produced only if alanine and valine were added to the reaction mixture. Using RNA 2, a polypeptide was produced only if leucine and serine and cysteine were added to the reaction mixture. Assuming that protein synthesis can start anywhere on the template, that the ET genetic code is nonoverlapping and linear, and that each codon is the same length (like the terrestrial triplet code), how many nucleotides does an ET codon contain?



(a) 2
(b) 3
(c) 4
(d) 5
(e) 6


Answer: D

You have discovered an alien life-form that surprisingly uses DNA as its genetic material, makes RNA from DNA, and reads the information from RNA to make protein using ribosomes and tRNAs, which read triplet codons. Because it is your job to decipher the genetic code for this alien, you synthesize some artificial RNA molecules and examine the protein products produced from these RNA molecules in a cell-free translation system using purified alien tRNAs and ribosomes. You obtain the results shown in Table Q7-68. From this information, which of the following peptides can be produced from poly UAUC?

10:49

You have discovered an alien life-form that surprisingly uses DNA as its genetic material, makes RNA from DNA, and reads the information from RNA to make protein using ribosomes and tRNAs, which read triplet codons. Because it is your job to decipher the genetic code for this alien, you synthesize some artificial RNA molecules and examine the protein products produced from these RNA molecules in a cell-free translation system using purified alien tRNAs and ribosomes. You obtain the results shown in Table Q7-68. From this information, which of the following peptides can be produced from poly UAUC?



(a) Ile-Phe-Val-Tyr
(b) Tyr-Ser-Phe-Ala
(c) Ile-Lys-His-Tyr
(d) Cys-Pro-Lys-Ala


Answer: D

When using a repeating trinucleotide sequence (such as 5'-AAC-3') in a cell-free translation system, you will obtain:

10:48

When using a repeating trinucleotide sequence (such as 5'-AAC-3') in a cell-free translation system, you will obtain:



(a) three different types of peptides, each made up of a single amino acid
(b) peptides made up of three different amino acids in random order
(c) peptides made up of three different amino acids, each alternating with each other in a repetitive fashion
(d) polyasparagine, as the codon for asparagine is AAC


Answer: A

You are studying a disease that is caused by a virus, but when you purify the virus particles and analyze them you find they contain no trace of DNA. Which of the following molecules are likely to contain the genetic information of the virus?

10:47

You are studying a disease that is caused by a virus, but when you purify the virus particles and analyze them you find they contain no trace of DNA. Which of the following molecules are likely to contain the genetic information of the virus?



(a) high-energy phosphate groups
(b) RNA
(c) lipids
(d) carbohydrates


Answer: B

According to current thinking, the minimum requirement for life to have originated on Earth was the formation of a _______________.

10:44

According to current thinking, the minimum requirement for life to have originated on Earth was the formation of a _______________.



(a) molecule that could provide a template for the production of a complementary molecule.
(b) double-stranded DNA helix.
(c) molecule that could direct protein synthesis.
(d) molecule that could catalyze its own replication.


Answer: D

Which of the following statements about the proteasome is false?

10:44

Which of the following statements about the proteasome is false?



(a) Ubiquitin is a small protein that is covalently attached to proteins to mark them for delivery to the proteasome.
(b) Proteases reside in the central cylinder of a proteasome.
(c) Misfolded proteins are delivered to the proteasome, where they are sequestered from the cytoplasm and can attempt to refold.
(d) The protein stoppers that surround the central cylinder of the proteasome use the energy from ATP hydrolysis to move proteins into the proteasome inner chamber.


Answer: C

Which of the following methods is not used by cells to regulate the amount of a protein in the cell?

10:43

Which of the following methods is not used by cells to regulate the amount of a protein in the cell?



(a) Genes can be transcribed into mRNA with different efficiencies.
(b) Many ribosomes can bind to a single mRNA molecule.
(c) Proteins can be tagged with ubiquitin, marking them for degradation.
(d) Nuclear pore complexes can regulate the speed at which newly synthesized proteins are exported from the nucleus into the cytoplasm.


Answer: D

The concentration of a particular protein, X, in a normal human cell rises gradually from a low point, immediately after cell division, to a high point, just before cell division, and then drops sharply. The level of its mRNA in the cell remains fairly constant throughout this time. Protein X is required for cell growth and survival, but the drop in its level just before cell division is essential for division to proceed. You have isolated a line of human cells that grow in size in culture but cannot divide, and on analyzing these mutants, you find that levels of X mRNA in the mutant cells are normal. Which of the following mutations in the gene for X could explain these results?

10:43

The concentration of a particular protein, X, in a normal human cell rises gradually from a low point, immediately after cell division, to a high point, just before cell division, and then drops sharply. The level of its mRNA in the cell remains fairly constant throughout this time. Protein X is required for cell growth and survival, but the drop in its level just before cell division is essential for division to proceed. You have isolated a line of human cells that grow in size in culture but cannot divide, and on analyzing these mutants, you find that levels of X mRNA in the mutant cells are normal. Which of the following mutations in the gene for X could explain these results?



(a) the introduction of a stop codon that truncates protein X at the fourth amino acid
(b) a change of the first ATG codon to CCA
(c) the deletion of a sequence that encodes sites at which ubiquitin can be attached to the protein
(d) a change at a splice site that prevents splicing of the RNA


Answer: C

You have discovered a protein that inhibits translation. When you add this inhibitor to a mixture capable of translating human mRNA and centrifuge the mixture to separate polyribosomes and single ribosomes, you obtain the results shown in Figure Q7-57. Which of the following interpretations is consistent with these observations?

10:43

You have discovered a protein that inhibits translation. When you add this inhibitor to a mixture capable of translating human mRNA and centrifuge the mixture to separate polyribosomes and single ribosomes, you obtain the results shown in Figure Q7-57. Which of the following interpretations is consistent with these observations?



(a) The protein binds to the small ribosomal subunit and increases the rate of initiation of translation.
(b) The protein binds to sequences in the 5' region of the mRNA and inhibits the rate of initiation of translation.
(c) The protein binds to the large ribosomal subunit and slows down elongation of the polypeptide chain.
(d) The protein binds to sequences in the 3' region of the mRNA and prevents termination of translation.


Answer: B

Which of the following statements about prokaryotic mRNA molecules is false?

10:42

Which of the following statements about prokaryotic mRNA molecules is false?



(a) A single prokaryotic mRNA molecule can be translated into several proteins.
(b) Ribosomes must bind to the 5' cap before initiating translation.
(c) mRNAs are not polyadenylated.
(d) Ribosomes can start translating an mRNA molecule before transcription is complete.


Answer: B

A poison added to an in vitro translation mixture containing mRNA molecules with the sequence 5'-AUGAAAAAAAAAAAAUAA-3' has the following effect: the only product made is a Met-Lys dipeptide that remains attached to the ribosome. What is the most likely way in which the poison acts to inhibit protein synthesis?

10:42

A poison added to an in vitro translation mixture containing mRNA molecules with the sequence 5'-AUGAAAAAAAAAAAAUAA-3' has the following effect: the only product made is a Met-Lys dipeptide that remains attached to the ribosome. What is the most likely way in which the poison acts to inhibit protein synthesis?



(a) It inhibits peptidyl transferase activity.
(b) It inhibits movement of the small subunit relative to the large subunit.
(c) It inhibits release factor.
(d) It mimics release factor.


Answer: B

Which of the following statements is true?

10:42

Which of the following statements is true?



(a) Ribosomes are large RNA structures composed solely of rRNA.
(b) Ribosomes are synthesized entirely in the cytoplasm.
(c) rRNA contains the catalytic activity that joins amino acids together.
(d) A ribosome binds one tRNA at a time.


Answer: C

The ribosome is important for catalyzing the formation of peptide bonds. Which of the following statements is true?

10:41

The ribosome is important for catalyzing the formation of peptide bonds. Which of the following statements is true?



(a) The number of rRNA molecules that make up a ribosome greatly exceeds the number of protein molecules found in the ribosome.
(b) The large subunit of the ribosome is important for binding to the mRNA.
(c) The catalytic site for peptide bond formation is formed primarily from an rRNA.
(d) Once the large and small subunits of the ribosome assemble, they will not separate from each other until degraded by the proteasome.


Answer: C

What do you predict would happen if you created a tRNA with an anticodon of 5'-CAA-3' that is charged with methionine, and added this modified tRNA to a cell-free translation system that has all the normal components required for translating RNAs?

10:41

What do you predict would happen if you created a tRNA with an anticodon of 5'-CAA-3' that is charged with methionine, and added this modified tRNA to a cell-free translation system that has all the normal components required for translating RNAs?



(a) methionine would be incorporated into proteins at some positions where glutamine should be
(b) methionine would be incorporated into proteins at some positions where leucine should be
(c) methionine would be incorporated into proteins at some positions where valine should be
(d) translation would no longer be able to initiate


Answer: B

A mutation in the tRNA for the amino acid lysine results in the anticodon sequence 5'-UAU-3' (instead of 5'-UUU-3'). Which of the following aberrations in protein synthesis might this tRNA cause?

10:41

A mutation in the tRNA for the amino acid lysine results in the anticodon sequence 5'-UAU-3' (instead of 5'-UUU-3'). Which of the following aberrations in protein synthesis might this tRNA cause?



(a) read-through of stop codons
(b) substitution of lysine for isoleucine
(c) substitution of lysine for tyrosine
(d) substitution of lysine for phenylalanine


Answer: B

A strain of yeast translates mRNA into protein inaccurately. Individual molecules of a particular protein isolated from this yeast have variations in the first 11 amino acids compared with the sequence of the same protein isolated from normal yeast cells, as listed in Figure Q7-45. What is the most likely cause of this variation in protein sequence?

10:41

A strain of yeast translates mRNA into protein inaccurately. Individual molecules of a particular protein isolated from this yeast have variations in the first 11 amino acids compared with the sequence of the same protein isolated from normal yeast cells, as listed in Figure Q7-45. What is the most likely cause of this variation in protein sequence?



(a) a mutation in the DNA coding for the protein
(b) a mutation in the anticodon of the isoleucine-tRNA (tRNAIle)
(c) a mutation in the isoleucyl-tRNA synthetase that decreases its ability to distinguish between different amino acids
(d) a mutation in the isoleucyl-tRNA synthetase that decreases its ability to distinguish between different tRNA molecules


Answer: C

Below is the sequence from the 3' end of an mRNA.

10:40

Below is the sequence from the 3' end of an mRNA.


5'-CCGUUACCAGGCCUCAUUAUUGGUAACGGAAAAAAAAAAAAAA-3'

If you were told that this sequence contains the stop codon for the protein encoded by this mRNA, what is the anticodon on the tRNA in the P site of the ribosome when release factor binds to the A site?


(a) 5'-CCA-3'
(b) 5'-CCG-3'
(c) 5'-UGG-3'
(d) 5'-UUA-3'


Answer: A

Which of the following statements about the genetic code is correct?

10:36

Which of the following statements about the genetic code is correct?



(a) All codons specify more than one amino acid.
(b) The genetic code is redundant.
(c) All amino acids are specified by more than one codon.
(d) All codons specify an amino acid.


Answer: B

snRNAs ________.

10:36

snRNAs ________.



(a) are translated into snRNPs.
(b) are important for producing mature mRNA transcripts in bacteria.
(c) are removed by the spliceosome during RNA splicing.
(d) can bind to specific sequences at intron-exon boundaries through complementary base-pairing.


Answer: D

Genes in eukaryotic cells often have intronic sequences coded for within the DNA. These sequences are ultimately not translated into proteins. Why?

10:36

Genes in eukaryotic cells often have intronic sequences coded for within the DNA. These sequences are ultimately not translated into proteins. Why?



(a) Intronic sequences are removed from RNA molecules by the spliceosome, which works in the nucleus.
(b) Introns are not transcribed by RNA polymerase.
(c) Introns are removed by catalytic RNAs in the cytoplasm.
(d) The ribosome will skip over intron sequences when translating RNA into protein.


Answer: A

Which of the following statements about RNA splicing is false?

10:36

Which of the following statements about RNA splicing is false?



(a) Conventional introns are not found in bacterial genes.
(b) For a gene to function properly, every exon must be removed from the primary transcript in the same fashion on every mRNA molecule produced from the same gene.
(c) Small RNA molecules in the nucleus perform the splicing reactions necessary for the removal of introns.
(d) Splicing occurs after the 5' cap has been added to the end of the primary transcript.


Answer: B

Total nucleic acids are extracted from a culture of yeast cells and are then mixed with resin beads to which the polynucleotide 5'-TTTTTTTTTTTTTTTTTTTTTTTTT-3' has been covalently attached. After a short incubation, the beads are then extracted from the mixture. When you analyze the cellular nucleic acids that have stuck to the beads, which of the following is most abundant?

10:35

Total nucleic acids are extracted from a culture of yeast cells and are then mixed with resin beads to which the polynucleotide 5'-TTTTTTTTTTTTTTTTTTTTTTTTT-3' has been covalently attached. After a short incubation, the beads are then extracted from the mixture. When you analyze the cellular nucleic acids that have stuck to the beads, which of the following is most abundant?



(a) DNA
(b) tRNA
(c) rRNA
(d) mRNA


Answer: D

Transcription in bacteria differs from transcription in a eukaryotic cell because _______________.

10:35

Transcription in bacteria differs from transcription in a eukaryotic cell because _______________. 



(a) RNA polymerase (along with its sigma subunit) can initiate transcription on its own.
(b) RNA polymerase (along with its sigma subunit) requires the general transcription factors to assemble at the promoter before polymerase can begin transcription.
(c) the sigma subunit must associate with the appropriate type of RNA polymerase to produce mRNAs.
(d) RNA polymerase must be phosphorylated at its C-terminal tail for transcription to proceed.


Answer: A

You have a bacterial strain with a mutation that removes the transcription termination signal from the Abd operon. Which of the following statements describes the most likely effect of this mutation on Abd transcription?

10:35

You have a bacterial strain with a mutation that removes the transcription termination signal from the Abd operon. Which of the following statements describes the most likely effect of this mutation on Abd transcription? 



(a) The Abd RNA will not be produced in the mutant strain.
(b) The Abd RNA from the mutant strain will be longer than normal.
(c) Sigma factor will not dissociate from RNA polymerase when the Abd operon is being transcribed in the mutant strain.
(d) RNA polymerase will move in a backward fashion at the Abd operon in the mutant strain.


Answer: B

There are several reasons why the primase used to make the RNA primer for DNA replication is not suitable for gene transcription. Which of the statements below is not one of those reasons?

10:34

There are several reasons why the primase used to make the RNA primer for DNA replication is not suitable for gene transcription. Which of the statements below is not one of those reasons?



(a) Primase initiates RNA synthesis on a single-stranded DNA template.
(b) Primase can initiate RNA synthesis without the need for a base-paired primer.
(c) Primase synthesizes only RNAs of about 5-20 nucleotides in length.
(d) The RNA synthesized by primase remains base-paired to the DNA template.


Answer: B

Which of the following might decrease the transcription of only one specific gene in a bacterial cell?

10:34

Which of the following might decrease the transcription of only one specific gene in a bacterial cell?




(a) a decrease in the amount of sigma factor
(b) a decrease in the amount of RNA polymerase
(c) a mutation that introduced a stop codon into the DNA that precedes the gene's coding sequence
(d) a mutation that introduced extensive sequence changes into the DNA that precedes the gene's transcription start site


Answer: D

The sigma subunit of bacterial RNA polymerase ________.

10:34

The sigma subunit of bacterial RNA polymerase ________.



(a) contains the catalytic activity of the polymerase.
(b) remains part of the polymerase throughout transcription.
(c) recognizes promoter sites in the DNA.
(d) recognizes transcription termination sites in the DNA.


Answer: C

You have a segment of DNA that contains the following sequence:

10:34

You have a segment of DNA that contains the following sequence:


5'-GGACTAGACAATAGGGACCTAGAGATTCCGAAA-3'
3'-CCTGATCTGTTATCCCTGGATCTCTAAGGCTTT-5'

You know that the RNA transcribed from this segment contains the following sequence:

5'-GGACUAGACAAUAGGGACCUAGAGAUUCCGAAA-3'

Which of the following choices best describes how transcription occurs?


(a) the top strand is the template strand; RNA polymerase moves along this strand from 5' to 3'
(b) the top strand is the template strand; RNA polymerase moves along this strand from 3' to 5'
(c) the bottom strand is the template strand; RNA polymerase moves along this strand from 5' to 3'
(d) the bottom strand is the template strand; RNA polymerase moves along this strand from 3' to 5'


Answer: D

You have a piece of DNA that includes the following sequence:

10:33

You have a piece of DNA that includes the following sequence:


5'-ATAGGCATTCGATCCGGATAGCAT-3'
3'-TATCCGTAAGCTAGGCCTATCGTA-5'

Which of the following RNA molecules could be transcribed from this piece of DNA?


(a) 5'-UAUCCGUAAGCUAGGCCUAUGCUA-3'
(b) 5'-AUAGGCAUUCGAUCCGGAUAGCAU-3'
(c) 5'-UACGAUAGGCCUAGCUUACGGAUA-3'
(d) none of the above


Answer: B

Which one of the following is the main reason that a typical eukaryotic gene is able to respond to a far greater variety of regulatory signals than a typical prokaryotic gene or operon?

10:33

Which one of the following is the main reason that a typical eukaryotic gene is able to respond to a far greater variety of regulatory signals than a typical prokaryotic gene or operon?



(a) Eukaryotes have three types of RNA polymerase.
(b) Eukaryotic RNA polymerases require general transcription factors.
(c) The transcription of a eukaryotic gene can be influenced by proteins that bind far from the promoter.
(d) Prokaryotic genes are packaged into nucleosomes.


Answer: C

Which of the following molecules of RNA would you predict to be the most likely to fold into a specific structure as a result of intramolecular base-pairing?

10:33

Which of the following molecules of RNA would you predict to be the most likely to fold into a specific structure as a result of intramolecular base-pairing?



(a) 5'-CCCUAAAAAAAAAAAAAAAAUUUUUUUUUUUUUUUUAGGG-3'
(b) 5'-UGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUG-3'
(c) 5'-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-3'
(d) 5'-GGAAAAGGAGAUGGGCAAGGGGAAAAGGAGAUGGGCAAGG-3'


Answer: A

Unlike DNA, which typically forms a helical structure, different molecules of RNA can fold into a variety of three-dimensional shapes. This is largely because ________.

10:33

Unlike DNA, which typically forms a helical structure, different molecules of RNA can fold into a variety of three-dimensional shapes. This is largely because ________.



(a) RNA contains uracil and uses ribose as the sugar.
(b) RNA bases cannot form hydrogen bonds with each other.
(c) RNA nucleotides use a different chemical linkage between nucleotides compared to DNA.
(d) RNA is single-stranded.


Answer: D

Which of the following statements is false?

10:32

Which of the following statements is false?



(a) A new RNA molecule can begin to be synthesized from a gene before the previous RNA molecule's synthesis is completed.
(b) If two genes are to be expressed in a cell, these two genes can be transcribed with different efficiencies.
(c) RNA polymerase is responsible for both unwinding the DNA helix and catalyzing the formation of the phosphodiester bonds between nucleotides.
(d) Unlike DNA, RNA uses a uracil base and a deoxyribose sugar.


Answer: D

Transcription is similar to DNA replication in that ________.

10:32

Transcription is similar to DNA replication in that ________.



(a) an RNA transcript is synthesized discontinuously and the pieces are then joined together.
(b) it uses the same enzyme as that used to synthesize RNA primers during DNA replication.
(c) the newly synthesized RNA remains paired to the template DNA.
(d) nucleotide polymerization occurs only in the 5'-to-3' direction.


Answer: D

RNA in cells differs from DNA in that ________.

10:32

RNA in cells differs from DNA in that ________.



(a) it contains the base uracil, which pairs with cytosine.
(b) it is single-stranded and cannot form base pairs.
(c) it is single-stranded and can fold up into a variety of structures.
(d) the sugar ribose contains fewer oxygen atoms than does deoxyribose.


Answer: C

Consider two genes that are next to each other on a chromosome, as arranged in Figure Q7-3. Which of the following statements is true?

10:32

Consider two genes that are next to each other on a chromosome, as arranged in Figure Q7-3. Which of the following statements is true?



(a) The two genes must be transcribed into RNA using the same strand of DNA.
(b) If gene A is transcribed in a cell, gene B cannot be transcribed.
(c) Gene A and gene B can be transcribed at different rates, producing different amounts of RNA within the same cell.
(d) If gene A is transcribed in a cell, gene B must be transcribed.


Answer: C

The events listed below are all necessary for homologous recombination to occur properly:

10:31

The events listed below are all necessary for homologous recombination to occur properly:


A. Holliday junction cut and ligated
B. strand invasion
C. DNA synthesis
D. DNA ligation
E. double-strand break
F. nucleases create uneven strands
Which of the following is the correct order of events during homologous recombination?


(a) E, B, F, D, C, A
(b) B, E, F, D, C, A
(c) C, E, F, B, D, A
(d) E, F, B, C, D, A


Answer: D

Recombination has occurred between the chromosome segments shown in Figure Q6-61. The genes A and B, and the recessive alleles a and b, are used as markers on the maternal and paternal chromosomes, respectively. After alignment and homologous recombination, the specific arrangements of A, B, a, and b have changed. Which of the choices below correctly indicates the gene combination from the replication products of the maternal chromosome?

10:31

Recombination has occurred between the chromosome segments shown in Figure Q6-61. The genes A and B, and the recessive alleles a and b, are used as markers on the maternal and paternal chromosomes, respectively. After alignment and homologous recombination, the specific arrangements of A, B, a, and b have changed. Which of the choices below correctly indicates the gene combination from the replication products of the maternal chromosome?



(a) AB and aB
(b) ab and Ab
(c) AB and Ab
(d) aB and Ab


Answer: D

In addition to the repair of DNA double-strand breaks, homologous recombination is a mechanism for generating genetic diversity by swapping segments of parental chromosomes. During which process does swapping occur?

10:31

In addition to the repair of DNA double-strand breaks, homologous recombination is a mechanism for generating genetic diversity by swapping segments of parental chromosomes. During which process does swapping occur?



(a) DNA replication
(b) DNA repair
(c) meiosis
(d) transposition


Answer: C

Homologous recombination is an important mechanism in which organisms use a "backup" copy of the DNA as a template to fix double-strand breaks without loss of genetic information. Which of the following is not necessary for homologous recombination to occur?

10:31

Homologous recombination is an important mechanism in which organisms use a "backup" copy of the DNA as a template to fix double-strand breaks without loss of genetic information. Which of the following is not necessary for homologous recombination to occur?



(a) 3' DNA strand overhangs
(b) 5' DNA strand overhangs
(c) a long stretch of sequence similarity
(d) nucleases


Answer: B

Nonhomologous end joining can result in all but which of the following?

10:30

Nonhomologous end joining can result in all but which of the following?



(a) the recovery of lost nucleotides on a damaged DNA strand
(b) the interruption of gene expression
(c) loss of nucleotides at the site of repair
(d) translocations of DNA fragments to an entirely different chromosome


Answer: A

Select the option that best completes the following statement: Nonhomologous end joining is a process by which a double-stranded DNA end is joined ________.

10:30

Select the option that best completes the following statement: Nonhomologous end joining is a process by which a double-stranded DNA end is joined ________.



(a) to a similar stretch of sequence on the complementary chromosome.
(b) after repairing any mismatches.
(c) to the nearest available double-stranded DNA end.
(d) after filling in any lost nucleotides, helping to maintain the integrity of the DNA sequence.


Answer: C

Several members of the same family were diagnosed with the same kind of cancer when they were unusually young. Which one of the following is the most likely explanation for this phenomenon? It is possible that the individuals with the cancer have ____________.

10:30

Several members of the same family were diagnosed with the same kind of cancer when they were unusually young. Which one of the following is the most likely explanation for this phenomenon? It is possible that the individuals with the cancer have ____________.



(a) inherited a cancer-causing gene that suffered a mutation in an ancestor's somatic cells.
(b) inherited a mutation in a gene required for DNA synthesis.
(c) inherited a mutation in a gene required for mismatch repair.
(d) inherited a mutation in a gene required for the synthesis of purine nucleotides.


Answer: C

Which of the following statements is not an accurate statement about thymine dimers?

10:30

Which of the following statements is not an accurate statement about thymine dimers?



(a) Thymine dimers can cause the DNA replication machinery to stall.
(b) Thymine dimers are covalent links between thymidines on opposite DNA strands.
(c) Prolonged exposure to sunlight causes thymine dimers to form.
(d) Repair proteins recognize thymine dimers as a distortion in the DNA backbone.


Answer: B

Sometimes, chemical damage to DNA can occur just before DNA replication begins, not giving the repair system enough time to correct the error before the DNA is duplicated. This gives rise to mutation. If the adenosine in the sequence TCAT is depurinated and not repaired, which of the following is the point mutation you would observe after this segment has undergone two rounds of DNA replication?

10:29

Sometimes, chemical damage to DNA can occur just before DNA replication begins, not giving the repair system enough time to correct the error before the DNA is duplicated. This gives rise to mutation. If the adenosine in the sequence TCAT is depurinated and not repaired, which of the following is the point mutation you would observe after this segment has undergone two rounds of DNA replication?



(a) TCGT
(b) TAT
(c) TCT
(d) TGTT


Answer: C

Sometimes, chemical damage to DNA can occur just before DNA replication begins, not giving the repair system enough time to correct the error before the DNA is duplicated. This gives rise to mutation. If the cytosine in the sequence TCAT is deaminated and not repaired, which of the following is the point mutation you would observe after this segment has undergone two rounds of DNA replication?

10:29

Sometimes, chemical damage to DNA can occur just before DNA replication begins, not giving the repair system enough time to correct the error before the DNA is duplicated. This gives rise to mutation. If the cytosine in the sequence TCAT is deaminated and not repaired, which of the following is the point mutation you would observe after this segment has undergone two rounds of DNA replication?



(a) TTAT
(b) TUAT
(c) TGAT
(d) TAAT


Answer: A

In somatic cells, if a base is mismatched in one new daughter strand during DNA replication, and is not repaired, what fraction of the DNA duplexes will have a permanent change in the DNA sequence after the second round of DNA replication?

10:29

In somatic cells, if a base is mismatched in one new daughter strand during DNA replication, and is not repaired, what fraction of the DNA duplexes will have a permanent change in the DNA sequence after the second round of DNA replication?



(a) 1/2
(b) 1/4
(c) 1/8
(d) 1/16


Answer: B

You are examining the DNA sequences that code for the enzyme phosphofructokinase in skinks and Komodo dragons. You notice that the coding sequence that actually directs the sequence of amino acids in the enzyme is very similar in the two organisms but that the surrounding sequences vary quite a bit. What is the most likely explanation for this?

10:28

You are examining the DNA sequences that code for the enzyme phosphofructokinase in skinks and Komodo dragons. You notice that the coding sequence that actually directs the sequence of amino acids in the enzyme is very similar in the two organisms but that the surrounding sequences vary quite a bit. What is the most likely explanation for this?




(a) Coding sequences are repaired more efficiently.
(b) Coding sequences are replicated more accurately.
(c) Coding sequences are packaged more tightly in the chromosomes to protect them from DNA damage.
(d) Mutations in coding sequences are more likely to be deleterious to the organism than mutations in noncoding sequences.


Answer: D

Human beings with the inherited disease xeroderma pigmentosum have serious problems with lesions on their skin and often develop skin cancer with repeated exposure to sunlight. What type of DNA damage is not being recognized in the cells of these individuals?

10:28

Human beings with the inherited disease xeroderma pigmentosum have serious problems with lesions on their skin and often develop skin cancer with repeated exposure to sunlight. What type of DNA damage is not being recognized in the cells of these individuals?



(a) chemical damage
(b) X-ray irradiation damage
(c) mismatched bases
(d) ultraviolet irradiation damage


Answer: D

The repair of mismatched base pairs or damaged nucleotides in a DNA strand requires a multistep process. Which choice below describes the known sequence of events in this process?

10:28

The repair of mismatched base pairs or damaged nucleotides in a DNA strand requires a multistep process. Which choice below describes the known sequence of events in this process?



(a) DNA damage is recognized, the newly synthesized strand is identified by an existing nick in the backbone, a segment of the new strand is removed by repair proteins, the gap is filled by DNA polymerase, and the strand is sealed by DNA ligase.
(b) DNA repair polymerase simultaneously removes bases ahead of it and polymerizes the correct sequence behind it as it moves along the template. DNA ligase seals the nicks in the repaired strand.
(c) DNA damage is recognized, the newly synthesized strand is identified by an existing nick in the backbone, a segment of the new strand is removed by an exonuclease, and the gap is repaired by DNA ligase.
(d) A nick in the DNA is recognized, DNA repair proteins switch out the wrong base and insert the correct base, and DNA ligase seals the nick.


Answer: A

A pregnant mouse is exposed to high levels of a chemical. Many of the mice in her litter are deformed, but when they are interbred with each other, all their offspring are normal. Which two of the following statements could explain these results?

10:27

A pregnant mouse is exposed to high levels of a chemical. Many of the mice in her litter are deformed, but when they are interbred with each other, all their offspring are normal. Which two of the following statements could explain these results?



(a) In the deformed mice, somatic cells but not germ cells were mutated.
(b) The original mouse's germ cells were mutated.
(c) In the deformed mice, germ cells but not somatic cells were mutated.
(d) The toxic chemical affects development but is not mutagenic.


Answer: A & D

Beside the distortion in the DNA backbone caused by a mismatched base pair, what additional mark is there on eukaryotic DNA to indicate which strand needs to be repaired?

10:27

Beside the distortion in the DNA backbone caused by a mismatched base pair, what additional mark is there on eukaryotic DNA to indicate which strand needs to be repaired?



(a) a nick in the template strand
(b) a chemical modification of the new strand
(c) a nick in the new strand
(d) a sequence gap in the new strand


Answer: C

Even though DNA polymerase has a proofreading function, it still introduces errors in the newly synthesized strand at a rate of 1 per 107 nucleotides. To what degree does the mismatch repair system decrease the error rate arising from DNA replication?

10:27

Even though DNA polymerase has a proofreading function, it still introduces errors in the newly synthesized strand at a rate of 1 per 107 nucleotides. To what degree does the mismatch repair system decrease the error rate arising from DNA replication?



(a) 2-fold
(b) 5-fold
(c) 10-fold
(d) 100-fold


Answer: D

Sickle-cell anemia is an example of an inherited disease. Individuals with this disorder have misshapen (sickle-shaped) red blood cells caused by a change in the sequence of the ß-globin gene. What is the nature of the change?

10:27

Sickle-cell anemia is an example of an inherited disease. Individuals with this disorder have misshapen (sickle-shaped) red blood cells caused by a change in the sequence of the ß-globin gene. What is the nature of the change?



(a) chromosome loss
(b) base-pair change
(c) gene duplication
(d) base-pair insertion


Answer: B

Telomeres serve as caps at the ends of linear chromosomes. Which of the following is not true regarding the replication of telomeric sequences?

10:26

Telomeres serve as caps at the ends of linear chromosomes. Which of the following is not true regarding the replication of telomeric sequences?



(a) The lagging-strand telomeres are not completely replicated by DNA polymerase.
(b) Telomeres are made of repeating sequences.
(c) Additional repeated sequences are added to the template strand.
(d) The leading strand doubles back on itself to form a primer for the lagging strand.


Answer: D

The DNA duplex consists of two long covalent polymers wrapped around each other many times over their entire length. The separation of the DNA strands for replication causes the strands to be "overwound" in front of the replication fork. How does the cell relieve the torsional stress created along the DNA duplex during replication?

10:25

The DNA duplex consists of two long covalent polymers wrapped around each other many times over their entire length. The separation of the DNA strands for replication causes the strands to be "overwound" in front of the replication fork. How does the cell relieve the torsional stress created along the DNA duplex during replication?



(a) Nothing needs to be done because the two strands will be separated after replication is complete.
(b) Topoisomerases break the covalent bonds of the backbone allowing the local unwinding of DNA ahead of the replication fork.
(c) Helicase unwinds the DNA and rewinds it after replication is complete.
(d) DNA repair enzymes remove torsional stress as they replace incorrectly paired bases.


Answer: B

Which of the following statements about sequence proofreading during DNA replication is false?

10:25

Which of the following statements about sequence proofreading during DNA replication is false?



(a) The exonuclease activity is in a different domain of the DNA polymerase.
(b) The exonuclease activity cleaves DNA in the 5'-to-3' direction.
(c) The DNA proofreading activity occurs concomitantly with strand elongation.
(d) If an incorrect base is added, it is "unpaired" before removal.


Answer: B

DNA polymerases are processive, which means that they remain tightly associated with the template strand while moving rapidly and adding nucleotides to the growing daughter strand. Which piece of the replication machinery accounts for this characteristic?

10:24

DNA polymerases are processive, which means that they remain tightly associated with the template strand while moving rapidly and adding nucleotides to the growing daughter strand. Which piece of the replication machinery accounts for this characteristic?



(a) helicase
(b) sliding clamp
(c) single-strand binding protein
(d) primase


Answer: B

A molecule of bacterial DNA introduced into a yeast cell is imported into the nucleus but fails to replicate with the yeast DNA. Where do you think the block to replication arises? Choose the protein or protein complex below that is most probably responsible for the failure to replicate bacterial DNA. Give an explanation for your answer.

10:23

A molecule of bacterial DNA introduced into a yeast cell is imported into the nucleus but fails to replicate with the yeast DNA. Where do you think the block to replication arises? Choose the protein or protein complex below that is most probably responsible for the failure to replicate bacterial DNA. Give an explanation for your answer.



(a) primase
(b) helicase
(c) DNA polymerase
(d) initiator proteins



Answer: D

You have discovered an "Exo-" mutant form of DNA polymerase in which the 3'-to-5' exonuclease function has been destroyed but the ability to join nucleotides together is unchanged. Which of the following properties do you expect the mutant polymerase to have?

10:23

You have discovered an "Exo-" mutant form of DNA polymerase in which the 3'-to-5' exonuclease function has been destroyed but the ability to join nucleotides together is unchanged. Which of the following properties do you expect the mutant polymerase to have?



(a) It will polymerize in both the 5'-to-3' direction and the 3'-to-5' direction.
(b) It will polymerize more slowly than the normal Exo+ polymerase.
(c) It will fall off the template more frequently than the normal Exo+ polymerase.
(d) It will be more likely to generate mismatched base pairs.


Answer: D

Which of the following statements about the newly synthesized strand of a human chromosome is true?

10:22

Which of the following statements about the newly synthesized strand of a human chromosome is true?



(a) It was synthesized from a single origin solely by continuous DNA synthesis.
(b) It was synthesized from a single origin by a mixture of continuous and discontinuous DNA synthesis.
(c) It was synthesized from multiple origins solely by discontinuous DNA synthesis.
(d) It was synthesized from multiple origins by a mixture of continuous and discontinuous DNA synthesis.


Answer: D

Which of the following statements about the newly synthesized strand of a human chromosome is true?

10:22

Which of the following statements about the newly synthesized strand of a human chromosome is true?



(a) It was synthesized from a single origin solely by continuous DNA synthesis.
(b) It was synthesized from a single origin by a mixture of continuous and discontinuous DNA synthesis.
(c) It was synthesized from multiple origins solely by discontinuous DNA synthesis.
(d) It was synthesized from multiple origins by a mixture of continuous and discontinuous DNA synthesis.


Answer: D

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking single-strand binding protein were used to make the cell extracts?

10:21

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking single-strand binding protein were used to make the cell extracts?



(a) initiation of DNA synthesis
(b) Okazaki fragment synthesis
(c) leading-strand elongation
(d) lagging-strand completion


Answer: B

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking the exonuclease activity of DNA polymerase were used to make the cell extracts?

10:21

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking the exonuclease activity of DNA polymerase were used to make the cell extracts?



(a) initiation of DNA synthesis
(b) Okazaki fragment synthesis
(c) leading-strand elongation
(d) lagging-strand completion


Answer: D

Which of the following statements is true with respect to this in vitro replication system?

10:20

Which of the following statements is true with respect to this in vitro replication system?



(a) There will be only one leading strand and one lagging strand produced using this template.
(b) The leading and lagging strands compose one half of each newly synthesized DNA strand.
(c) The DNA replication machinery can assemble at multiple places on this plasmid.
(d) One daughter DNA molecule will be slightly shorter than the other.


Answer: B

DNA polymerase catalyzes the joining of a nucleotide to a growing DNA strand. What prevents this enzyme from catalyzing the reverse reaction?

10:20

DNA polymerase catalyzes the joining of a nucleotide to a growing DNA strand. What prevents this enzyme from catalyzing the reverse reaction?



(a) hydrolysis of pyrophosphate (PPi) to inorganic phosphate (Pi) + Pi
(b) release of PPi from the nucleotide
(c) hybridization of the new strand to the template
(d) loss of ATP as an energy source


Answer: A

The chromatin structure in eukaryotic cells is much more complicated than that observed in prokaryotic cells. This is thought to be the reason that DNA replication occurs much faster in prokaryotes. How much faster is it?

10:20

The chromatin structure in eukaryotic cells is much more complicated than that observed in prokaryotic cells. This is thought to be the reason that DNA replication occurs much faster in prokaryotes. How much faster is it?



(a) 2×
(b) 5×
(c) 10×
(d) 100×


Answer: C

Which of the following statements correctly explains what it means for DNA replication to be bidirectional?

10:20

Which of the following statements correctly explains what it means for DNA replication to be bidirectional? 



(a) The replication fork can open or close, depending on the conditions.
(b) The DNA replication machinery can move in either direction on the template strand.
(c) Replication-fork movement can switch directions when the fork converges on another replication fork.
(d) The replication forks formed at the origin move in opposite directions.


Answer: D

If the genome of the bacterium E. coli requires about 20 minutes to replicate itself, how can the genome of the fruit fly Drosophila be replicated in only 3 minutes?

10:19

If the genome of the bacterium E. coli requires about 20 minutes to replicate itself, how can the genome of the fruit fly Drosophila be replicated in only 3 minutes?



(a) The Drosophila genome is smaller than the E. coli genome.
(b) Eukaryotic DNA polymerase synthesizes DNA at a much faster rate than prokaryotic DNA polymerase.
(c) The nuclear membrane keeps the Drosophila DNA concentrated in one place in the cell, which increases the rate of polymerization.
(d) Drosophila DNA contains more origins of replication than E. coli DNA.


Answer: D

Initiator proteins bind to replication origins and disrupt hydrogen bonds between the two DNA strands being copied. Which of the factors below does not contribute to the relative ease of strand separation by initiator proteins?

10:18

Initiator proteins bind to replication origins and disrupt hydrogen bonds between the two DNA strands being copied. Which of the factors below does not contribute to the relative ease of strand separation by initiator proteins?



(a) replication origins are rich in A-T base pairs
(b) the reaction can occur at room temperature
(c) they only separate a few base pairs at a time
(d) once opened, other proteins of the DNA replication machinery bind to the origin


Answer: B

DNA replication is considered semiconservative because _______.

10:17

DNA replication is considered semiconservative because _______.



(a) after many rounds of DNA replication, the original DNA double helix is still intact.
(b) each daughter DNA molecule consists of two new strands copied from the parent DNA molecule.
(c) each daughter DNA molecule consists of one strand from the parent DNA molecule and one new strand.
(d) new DNA strands must be copied from a DNA template.


Answer: C

Most eukaryotic cells only express 20-30% of the genes they possess. The formation of heterochromatin maintains the other genes in a transcriptionally silent (unexpressed) state. Which histone modification directs the formation of the most common type of heterochromatin?

10:15

Most eukaryotic cells only express 20-30% of the genes they possess. The formation of heterochromatin maintains the other genes in a transcriptionally silent (unexpressed) state. Which histone modification directs the formation of the most common type of heterochromatin?



(a) H3 lysine 4 methylation
(b) H3 lysine 9 methylation
(c) H3 lysine 14 methylation
(d) H3 lysine 27 methylation


Answer: B

How do changes in histone modifications lead to changes in chromatin structure?

10:15

How do changes in histone modifications lead to changes in chromatin structure?



(a) They directly lead to changes in the positions of the core histones.
(b) They change the affinity between the histone octamer and the DNA.
(c) They help recruit other proteins to the chromatin.
(d) They cause the histone N-terminal tails to become hyperextended.


Answer: C

Which of the following best describes the mechanism by which chromatin-remodeling complexes "loosen" the DNA wrapped around the core histones?

10:14

Which of the following best describes the mechanism by which chromatin-remodeling complexes "loosen" the DNA wrapped around the core histones?



(a) They use energy derived from ATP hydrolysis to change the relative position of the DNA and the core histone octamer.
(b) They chemically modify the DNA, changing the affinity between the histone octamer and the DNA.
(c) They remove histone H1 from the linker DNA adjacent to the core histone octamer.
(d) They chemically modify core histones to alter the affinity between the histone octamer and the DNA.


Answer: A

When there is a well-established segment of heterochromatin on an interphase chromosome, there is usually a special barrier sequence that prevents the heterochromatin from expanding along the entire chromosome. Gene A, which is normally expressed, has been moved by DNA recombination near an area of heterochromatin. None of the daughter cells produced after this recombination event express gene A, even though its DNA sequence is unchanged. What is the best way to describe what has happened to the function of gene A in these cells?

10:14

When there is a well-established segment of heterochromatin on an interphase chromosome, there is usually a special barrier sequence that prevents the heterochromatin from expanding along the entire chromosome. Gene A, which is normally expressed, has been moved by DNA recombination near an area of heterochromatin. None of the daughter cells produced after this recombination event express gene A, even though its DNA sequence is unchanged. What is the best way to describe what has happened to the function of gene A in these cells?



(a) barrier destruction
(b) heterochromatization
(c) epigenetic inheritance
(d) euchromatin depletion


Answer: C

Methylation and acetylation are common changes made to histone H3, and the specific combination of these changes is sometimes referred to as the "histone code." Which of the following patterns will probably lead to gene silencing?

10:14

Methylation and acetylation are common changes made to histone H3, and the specific combination of these changes is sometimes referred to as the "histone code." Which of the following patterns will probably lead to gene silencing?



(a) lysine 9 methylation
(b) lysine 4 methylation and lysine 9 acetylation
(c) lysine 14 acetylation
(d) lysine 9 acetylation and lysine 14 acetylation


Answer: A

The N-terminal tail of histone H3 can be extensively modified, and depending on the number, location, and combination of these modifications, these changes may promote the formation of heterochromatin. What is the result of heterochromatin formation?

10:13

The N-terminal tail of histone H3 can be extensively modified, and depending on the number, location, and combination of these modifications, these changes may promote the formation of heterochromatin. What is the result of heterochromatin formation?



(a) increase in gene expression
(b) gene silencing
(c) recruitment of remodeling complexes
(d) displacement of histone H1


Answer: B

Although the chromatin structure of interphase and mitotic chromosomes is very compact, DNA-binding proteins and protein complexes must be able to gain access to the DNA molecule. Chromatin-remodeling complexes provide this access by _______.

10:13

Although the chromatin structure of interphase and mitotic chromosomes is very compact, DNA-binding proteins and protein complexes must be able to gain access to the DNA molecule. Chromatin-remodeling complexes provide this access by _______.



(a) recruiting other enzymes.
(b) modifying the N-terminal tails of core histones.
(c) using the energy of ATP hydrolysis to move nucleosomes.
(d) denaturing the DNA by interfering with hydrogen-bonding between base pairs.


Answer: C

Stepwise condensation of linear DNA happens in five different packing processes. Which of the following four processes has a direct requirement for histone H1?

10:13

Stepwise condensation of linear DNA happens in five different packing processes. Which of the following four processes has a direct requirement for histone H1?



(a) formation of "beads-on-a-string"
(b) formation of the 30-nm fiber
(c) looping of the 30-nm fiber
(d) packing of loops to form interphase chromosomes


Answer: B

The core histones are small, basic proteins that have a globular domain at the C-terminus and a long, extended conformation at the N-terminus. Which of the following is not true of the N-terminal "tail" of these histones?

10:13

The core histones are small, basic proteins that have a globular domain at the C-terminus and a long, extended conformation at the N-terminus. Which of the following is not true of the N-terminal "tail" of these histones? 



(a) It is subject to covalent modifications.
(b) It extends out of the nucleosome core.
(c) It binds to DNA in a sequence-specific manner.
(d) It helps DNA pack tightly.


Answer: C

The octameric histone core is composed of four different histone proteins, assembled in a stepwise manner. Once the core octamer has been formed, DNA wraps around it to form a nucleosome core particle. Which of the following histone proteins does not form part of the octameric core?

10:12

The octameric histone core is composed of four different histone proteins, assembled in a stepwise manner. Once the core octamer has been formed, DNA wraps around it to form a nucleosome core particle. Which of the following histone proteins does not form part of the octameric core?



(a) H4
(b) H2A
(c) H3
(d) H1


Answer: D

The classic "beads-on-a-string" structure is the most decondensed chromatin structure possible and is produced experimentally. Which chromatin components are not retained when this structure is generated?

10:12

The classic "beads-on-a-string" structure is the most decondensed chromatin structure possible and is produced experimentally. Which chromatin components are not retained when this structure is generated?



(a) linker histones
(b) linker DNA
(c) nucleosome core particles
(d) core histones


Answer: A

Specific regions of eukaryotic chromosomes contain sequence elements that are absolutely required for the proper transmission of genetic information from a mother cell to each daughter cell. Which of the following is not known to be one of these required elements in eukaryotes?

10:09

Specific regions of eukaryotic chromosomes contain sequence elements that are absolutely required for the proper transmission of genetic information from a mother cell to each daughter cell. Which of the following is not known to be one of these required elements in eukaryotes?



(a) terminators of replication
(b) origins of replication
(c) telomeres
(d) centromeres


Answer: A

Figure Q5-45 clearly depicts the nucleolus, a nuclear structure that looks like a large, dark region when stained. The other dark, speckled regions in this image are the locations of particularly compact chromosomal segments called ____________.

10:08

Figure Q5-45 clearly depicts the nucleolus, a nuclear structure that looks like a large, dark region when stained. The other dark, speckled regions in this image are the locations of particularly compact chromosomal segments called ____________.



(a) euchromatin.
(b) heterochromatin.
(c) nuclear pores.
(d) nucleosomes.


Answer: B

The chromosomes we typically see in images are isolated from mitotic cells. These mitotic chromosomes are in the most highly condensed form. Interphase cells contain chromosomes that are less densely packed and _______________.

10:08

The chromosomes we typically see in images are isolated from mitotic cells. These mitotic chromosomes are in the most highly condensed form. Interphase cells contain chromosomes that are less densely packed and _______________.



(a) occupy discrete territories in the nucleus.
(b) share the same nuclear territory as their homolog.
(c) are restricted to the nucleolus.
(d) are completely tangled with other chromosomes.


Answer: A

Which of the following questions would not be answered by using karyotyping?

10:08

Which of the following questions would not be answered by using karyotyping?



(a) Is the individual genetically female or male?
(b) Do any of the chromosomes contain pieces that belong to other chromosomes?
(c) Does the individual have an extra chromosome?
(d) Do any chromosomes contain point mutations?


Answer: D

The process of sorting human chromosome pairs by size and morphology is called karyotyping. A modern method employed for karyotyping is called chromosome painting. How are individual chromosomes "painted"?

10:08

The process of sorting human chromosome pairs by size and morphology is called karyotyping. A modern method employed for karyotyping is called chromosome painting. How are individual chromosomes "painted"?



(a) with a laser
(b) using fluorescent antibodies
(c) using fluorescent DNA molecules
(d) using green fluorescent protein


Answer: C

The human genome is a diploid genome. However, when germ-line cells produce gametes, these specialized cells are haploid. What is the total number of chromosomes found in each of the gametes (egg or sperm) in your body?

10:07

The human genome is a diploid genome. However, when germ-line cells produce gametes, these specialized cells are haploid. What is the total number of chromosomes found in each of the gametes (egg or sperm) in your body?



(a) 22
(b) 23
(c) 44
(d) 46


Answer: B

Fred Griffith studied two strains of Streptococcus pneumonia, one that causes a lethal infection when injected into mice, and a second that is harmless. He observed that pathogenic bacteria that have been killed by heating can no longer cause an infection. But when these heat-killed bacteria are mixed with live, harmless bacteria, this mixture is capable of infecting and killing a mouse. What did Griffith conclude from this experiment?

10:04

Fred Griffith studied two strains of Streptococcus pneumonia, one that causes a lethal infection when injected into mice, and a second that is harmless. He observed that pathogenic bacteria that have been killed by heating can no longer cause an infection. But when these heat-killed bacteria are mixed with live, harmless bacteria, this mixture is capable of infecting and killing a mouse. What did Griffith conclude from this experiment?



(a) The infectious strain cannot killed by heating.
(b) The heat-killed pathogenic bacteria "transformed" the harmless strain into a lethal one.
(c) The harmless strain somehow revived the heat-killed pathogenic bacteria.
(d) The mice had lost their immunity to infection with S. pneumoniae.


Answer: B

Several experiments were required to demonstrate how traits are inherited. Which scientist or team of scientists first demonstrated that cells contain some component that can be transferred to a new population of cells and permanently cause changes in the new cells?

10:03

Several experiments were required to demonstrate how traits are inherited. Which scientist or team of scientists first demonstrated that cells contain some component that can be transferred to a new population of cells and permanently cause changes in the new cells?



(a) Griffith
(b) Watson and Crick
(c) Avery, MacLeod, and McCarty
(d) Hershey and Chase


Answer: A

You are a virologist interested in studying the evolution of viral genomes. You are studying two newly isolated viral strains and have sequenced their genomes. You find that the genome of strain 1 contains 25% A, 55% G, 20% C, and 10% T. You report that you have isolated a virus with a single-stranded DNA genome. Based on what evidence can you make this conclusion?

10:03

You are a virologist interested in studying the evolution of viral genomes. You are studying two newly isolated viral strains and have sequenced their genomes. You find that the genome of strain 1 contains 25% A, 55% G, 20% C, and 10% T. You report that you have isolated a virus with a single-stranded DNA genome. Based on what evidence can you make this conclusion?



(a) single-stranded genomes always have a large percentage of purines
(b) using the formula: G - A = C + T
(c) Double-stranded genomes have equal amounts of A and T
(d) Single-stranded genomes have a higher rate of mutation


Answer: C

In a DNA double helix, __________.

10:03

In a DNA double helix, __________.



(a) the two DNA strands are identical.
(b) purines pair with purines.
(c) thymine pairs with cytosine.
(d) the two DNA strands run antiparallel.


Answer: D

In the 1940s, proteins were thought to be the more likely molecules to house genetic information. What was the primary reason that DNA was not originally believed to be the genetic material?

10:03

In the 1940s, proteins were thought to be the more likely molecules to house genetic information. What was the primary reason that DNA was not originally believed to be the genetic material?



(a) DNA has a high density of negative charges.
(b) Nucleotides were known to be a source of chemical energy for the cell.
(c) Both protein and nucleic acids were found to be components of chromosomes.
(d) DNA was found to contain only four different chemical building blocks.


Answer: D

Mitotic chromosomes were first visualized with the use of very simple tools: a basic light microscope and some dyes. Which of the following characteristics of mitotic chromosomes reflects how they were named?

10:02

Mitotic chromosomes were first visualized with the use of very simple tools: a basic light microscope and some dyes. Which of the following characteristics of mitotic chromosomes reflects how they were named?



(a) motion
(b) color
(c) shape
(d) location


Answer: B

Many of the breakthroughs in modern biology came after Watson and Crick published their model of DNA in 1953. However, chromosomes were identified earlier. In what decade did scientists first identify chromosomes?

10:02

Many of the breakthroughs in modern biology came after Watson and Crick published their model of DNA in 1953. However, chromosomes were identified earlier. In what decade did scientists first identify chromosomes?



(a) 1880s
(b) 1920s
(c) 1940s
(d) 1780s


Answer: A

Instead of studying one or two proteins or protein complexes present in the cell at any given time, we can now look at a snapshot of all proteins being expressed in cells being grown in specific conditions. This large-scale, systematic approach to the study of proteins is called _______________.

10:01

Instead of studying one or two proteins or protein complexes present in the cell at any given time, we can now look at a snapshot of all proteins being expressed in cells being grown in specific conditions. This large-scale, systematic approach to the study of proteins is called _______________.



(a) proteomics.
(b) structural biology.
(c) systems biology.
(d) genomics.


Answer: B

Determining a protein's sequence, site of covalent modification, or entire three- dimensional structure requires the careful analysis of complex data sets. Which of the data sets below would you have to interpret to solve the structure of a protein by using X- ray crystallography?

10:00

Determining a protein's sequence, site of covalent modification, or entire three- dimensional structure requires the careful analysis of complex data sets. Which of the data sets below would you have to interpret to solve the structure of a protein by using X- ray crystallography?



Answer: B

Energy required by the cell is generated in the form of ATP. ATP is hydrolyzed to power many of the cellular processes, increasing the pool of ADP. As the relative amount of ADP molecules increases, they can bind to glycolytic enzymes, which will lead to the production of more ATP. The best way to describe this mechanism of regulation is ___________.

09:58

Energy required by the cell is generated in the form of ATP. ATP is hydrolyzed to power many of the cellular processes, increasing the pool of ADP. As the relative amount of ADP molecules increases, they can bind to glycolytic enzymes, which will lead to the production of more ATP. The best way to describe this mechanism of regulation is ___________.



(a) feedback inhibition.
(b) oxidative phosphorylation.
(c) allosteric activation.
(d) substrate-level phosphorylation.


Answer: C

The phosphorylation of a protein is typically associated with a change in activity, the assembly of a protein complex, or the triggering of a downstream signaling cascade. The addition of ubiquitin, a small polypeptide, is another type of covalent modification that can affect the protein function. Ubiquitylation often results in ______________.

09:58

The phosphorylation of a protein is typically associated with a change in activity, the assembly of a protein complex, or the triggering of a downstream signaling cascade. The addition of ubiquitin, a small polypeptide, is another type of covalent modification that can affect the protein function. Ubiquitylation often results in ______________.




(a) membrane association.
(b) protein degradation.
(c) protein secretion.
(d) nuclear translocatiBiologyon.


Answer: B

Proteins can assemble to form large complexes that work coordinately, like moving parts inside a single machine. Which of the following steps in modulating the activity of a complex protein machine is least likely to be directly affected by ATP or GTP hydrolysis?

09:58

Proteins can assemble to form large complexes that work coordinately, like moving parts inside a single machine. Which of the following steps in modulating the activity of a complex protein machine is least likely to be directly affected by ATP or GTP hydrolysis?



(a) translation of protein components
(b) conformational change of protein components
(c) complex assembly
(d) complex disassembly


Answer: A

Motor proteins use the energy in ATP to transport organelles, rearrange elements of the cytoskeleton during cell migration, and move chromosomes during cell division. Which of the following mechanisms is sufficient to ensure the unidirectional movement of a motor protein along its substrate?

09:58

Motor proteins use the energy in ATP to transport organelles, rearrange elements of the cytoskeleton during cell migration, and move chromosomes during cell division. Which of the following mechanisms is sufficient to ensure the unidirectional movement of a motor protein along its substrate?



(a) A conformational change is coupled to the release of a phosphate (Pi).
(b) The substrate on which the motor moves has a conformational polarity.
(c) A conformational change is coupled to the binding of ADP.
(d) A conformational change is linked to ATP hydrolysis.


Answer: D

The Ras protein is a GTPase that functions in many growth-factor signaling pathways. In its active form, with GTP bound, it transmits a downstream signal that leads to cell proliferation; in its inactive form, with GDP bound, the signal is not transmitted. Mutations in the gene for Ras are found in many cancers. Of the choices below, which alteration of Ras activity is most likely to contribute to the uncontrolled growth of cancer cells?

09:57

The Ras protein is a GTPase that functions in many growth-factor signaling pathways. In its active form, with GTP bound, it transmits a downstream signal that leads to cell proliferation; in its inactive form, with GDP bound, the signal is not transmitted. Mutations in the gene for Ras are found in many cancers. Of the choices below, which alteration of Ras activity is most likely to contribute to the uncontrolled growth of cancer cells?



(a) a change that prevents Ras from being made
(b) a change that increases the affinity of Ras for GDP
(c) a change that decreases the affinity of Ras for GTP
(d) a change that decreases the rate of hydrolysis of GTP by Ras


Answer: D

Which of the following statements about allostery is true?

02:38

Which of the following statements about allostery is true?



(a) Allosteric regulators are often products of other chemical reactions in the same biochemical pathway.
(b) Allosteric regulation is always used for negative regulation of enzyme activity.
(c) Enzymes are the only types of proteins that are subject to allosteric regulation.
(d) Binding of allosteric molecules usually locks an enzyme in its current conformation, such that the enzyme cannot adopt a different conformation.


Answer: A

The biosynthetic pathway for the two amino acids E and H is shown schematically in Figure Q4-60. You are able to show that E inhibits enzyme V, and H inhibits enzyme X. Enzyme T is most likely to be subject to feedback inhibition by _______ alone.

02:38

The biosynthetic pathway for the two amino acids E and H is shown schematically in Figure Q4-60. You are able to show that E inhibits enzyme V, and H inhibits enzyme X. Enzyme T is most likely to be subject to feedback inhibition by _______ alone.



(a) H
(b) B
(c) C
(d) E


Answer: C

For some proteins, small molecules are integral to their structure and function. Enzymes can synthesize some of these small molecules, whereas others, called vitamins, must be ingested in the food we eat. Which of the following molecules is not classified as a vitamin but does require the ingestion of a vitamin for its production?

02:37

For some proteins, small molecules are integral to their structure and function. Enzymes can synthesize some of these small molecules, whereas others, called vitamins, must be ingested in the food we eat. Which of the following molecules is not classified as a vitamin but does require the ingestion of a vitamin for its production?



(a) retinal
(b) biotin
(c) zinc
(d) heme


Answer: A

Studies conducted with a lysozyme mutant that contains an Aspa`Asn change at position 52 and a Glua`Gln change at position 35 exhibited almost a complete loss in enzymatic activity. What is the most likely explanation for the decrease in enzyme activity in the mutant?

02:37

Studies conducted with a lysozyme mutant that contains an Aspa`Asn change at position 52 and a Glua`Gln change at position 35 exhibited almost a complete loss in enzymatic activity. What is the most likely explanation for the decrease in enzyme activity in the mutant?



(a) increased affinity for substrate
(b) absence of negative charges in the active site
(c) change in the active-site scaffold
(d) larger amino acids in the active site decreases the affinity for substrate


Answer: B

Which of the following mechanisms best describes the manner in which lysozyme lowers the energy required for its substrate to reach its transition-state conformation?

02:37

Which of the following mechanisms best describes the manner in which lysozyme lowers the energy required for its substrate to reach its transition-state conformation?



(a) by binding two molecules and orienting them in a way that favors a reaction between them
(b) by altering the shape of the substrate to mimic the conformation of the transition state
(c) by speeding up the rate at which water molecules collide with the substrate
(d) by binding irreversibly to the substrate so that it cannot dissociate


Answer: C

Antibody production is an indispensable part of our immune response, but it is not the only defense our bodies have. Which of the following is observed during an infection that is not a result of antibody-antigen interactions?

02:36

Antibody production is an indispensable part of our immune response, but it is not the only defense our bodies have. Which of the following is observed during an infection that is not a result of antibody-antigen interactions?



(a) B cell proliferation
(b) aggregation of viral particles
(c) systemic temperature increase
(d) antibody secretion


Answer: C

The process of generating monoclonal antibodies is labor-intensive and expensive. An alternative is to use polyclonal antibodies. A subpopulation of purified polyclonal antibodies that recognize a particular antigen can be isolated by chromatography. Which type of chromatography is used for this purpose?

02:36

The process of generating monoclonal antibodies is labor-intensive and expensive. An alternative is to use polyclonal antibodies. A subpopulation of purified polyclonal antibodies that recognize a particular antigen can be isolated by chromatography. Which type of chromatography is used for this purpose?



(a) affinity
(b) ion-exchange
(c) gel-filtration
(d) any of the above


Answer: A

Cyclic AMP (cAMP) is a small molecule that associates with its binding site with a high degree of specificity. Which types of noncovalent interactions are the most important for providing the "hand in a glove" binding of cAMP?

02:36

Cyclic AMP (cAMP) is a small molecule that associates with its binding site with a high degree of specificity. Which types of noncovalent interactions are the most important for providing the "hand in a glove" binding of cAMP?



(a) hydrogen bonds
(b) electrostatic interactions
(c) van der Waals interactions
(d) hydrophobic interactions


Answer: A

Proteins bind selectively to small-molecule targets called ligands. The selection of one ligand out of a mixture of possible ligands depends on the number of weak, noncovalent interactions in the protein's ligand-binding site. Where is the binding site typically located in the protein structure?

02:36

Proteins bind selectively to small-molecule targets called ligands. The selection of one ligand out of a mixture of possible ligands depends on the number of weak, noncovalent interactions in the protein's ligand-binding site. Where is the binding site typically located in the protein structure?



(a) on the surface of the protein
(b) inside a cavity on the protein surface
(c) buried in the interior of the protein
(d) forms on the surface of the protein in the presence of ligand


Answer: B

You have two purified samples of protein Y: the wild-type (nonmutated) protein and a mutant version with a single amino acid substitution. When washed through the same gel- filtration column, mutant protein Y runs through the column more slowly than the normal protein. Which of the following changes in the mutant protein is most likely to explain this result?

02:35

You have two purified samples of protein Y: the wild-type (nonmutated) protein and a mutant version with a single amino acid substitution. When washed through the same gel- filtration column, mutant protein Y runs through the column more slowly than the normal protein. Which of the following changes in the mutant protein is most likely to explain this result?



(a) the loss of a binding site on the mutant-protein surface through which protein Y normally forms dimers
(b) a change that results in the mutant protein acquiring an overall positive instead of a negative charge
(c) a change that results in the mutant protein being larger than the wild-type protein
(d) a change that results in the mutant protein having a slightly different shape from the wild-type protein


Answer: A

Globular proteins fold up into compact, spherical structures that have uneven surfaces. They tend to form multisubunit complexes, which also have a rounded shape. Fibrous proteins, in contrast, span relatively large distances within the cell and in the extracellular space. Which of the proteins below is not classified as a fibrous protein?

02:34

Globular proteins fold up into compact, spherical structures that have uneven surfaces. They tend to form multisubunit complexes, which also have a rounded shape. Fibrous proteins, in contrast, span relatively large distances within the cell and in the extracellular space. Which of the proteins below is not classified as a fibrous protein?



(a) elastase
(b) collagen
(c) keratin
(d) elastin


Answer: A

Protein structures have several different levels of organization. The primary structure of a protein is its amino acid sequence. The secondary and tertiary structures are more complicated. Consider the definitions below and select the one that best fits the term "protein domain."

02:34

Protein structures have several different levels of organization. The primary structure of a protein is its amino acid sequence. The secondary and tertiary structures are more complicated. Consider the definitions below and select the one that best fits the term "protein domain."



(a) a small cluster of a helices and ß sheets
(b) the tertiary structure of a substrate-binding pocket
(c) a complex of more than one polypeptide chain
(d) a protein segment that folds independently


Answer: D

ß Sheets can participate in the formation of amyloid fibers, which are insoluble protein aggregates. What drives the formation of amyloid fibers?

02:34

ß Sheets can participate in the formation of amyloid fibers, which are insoluble protein aggregates. What drives the formation of amyloid fibers?



(a) denaturation of proteins containing ß sheets
(b) extension of ß sheets into much longer ß strands
(c) formation of biofilms by infectious bacteria
(d) ß-sheet stabilization of abnormally folded proteins


Answer: D

Although all protein structures are unique, there are common structural building blocks that are referred to as regular secondary structures. Some proteins have a helices, some have ß sheets, and still others have a combination of both. What makes it possible for proteins to have these common structural elements?

02:32

Although all protein structures are unique, there are common structural building blocks that are referred to as regular secondary structures. Some proteins have a helices, some have ß sheets, and still others have a combination of both. What makes it possible for proteins to have these common structural elements?



(a) specific amino acid sequences
(b) side-chain interactions
(c) the hydrophobic-core interactions
(d) hydrogen bonds along the protein backbone


Answer: D

Typical folded proteins have a stability ranging from 7 to 15 kcal/mole at 37°C. Stability is a measure of the equilibrium between the folded (F) and unfolded (U) forms of the protein, with the unfolded form having a greater free energy (see Figure Q4-20). For a protein with a stability of 7.1 kcal/mole, calculate the fraction of protein that would be unfolded at equilibrium at 37°C. The equilibrium constant (Keq) is related to the free energy (?G°) by the equation Keq = 10-?G°/1.42.

02:32

Typical folded proteins have a stability ranging from 7 to 15 kcal/mole at 37°C. Stability is a measure of the equilibrium between the folded (F) and unfolded (U) forms of the protein, with the unfolded form having a greater free energy (see Figure Q4-20). For a protein with a stability of 7.1 kcal/mole, calculate the fraction of protein that would be unfolded at equilibrium at 37°C. The equilibrium constant (Keq) is related to the free energy (?G°) by the equation Keq = 10-?G°/1.42.



Answer: 1/100,000

The three-dimensional coordinates of atoms within a folded protein are determined experimentally. After researchers obtain a protein's structural details, they can use different techniques to highlight particular aspects of the structure. What visual model best displays a protein's secondary structures (a helices and ß sheets)?

02:32

The three-dimensional coordinates of atoms within a folded protein are determined experimentally. After researchers obtain a protein's structural details, they can use different techniques to highlight particular aspects of the structure. What visual model best displays a protein's secondary structures (a helices and ß sheets)?



(a) ribbon
(b) space-filling
(c) backbone
(d) wire


Answer: A

Molecular chaperones can work by creating an "isolation chamber." What is the purpose of this chamber?

02:32

Molecular chaperones can work by creating an "isolation chamber." What is the purpose of this chamber?



(a) The chamber acts as a garbage disposal, degrading improperly folded proteins so that they do not interact with properly folded proteins.
(b) This chamber is used to increase the local protein concentration, which will help speed up the folding process.
(c) This chamber serves to transport unfolded proteins out of the cell.
(d) This chamber serves to protect unfolded proteins from interacting with other proteins in the cytosol, until protein folding is completed.


Answer: D

Which of the following is not true of molecular chaperones?

02:31

Which of the following is not true of molecular chaperones?



(a) They assist polypeptide folding by helping the folding process follow the most energetically favorable pathway.
(b) They can isolate proteins from other components of the cells until folding is complete.
(c) They can interact with unfolded polypeptides in a way that changes the final fold of the protein.
(d) They help streamline the protein-folding process by making it a more efficient and reliable process inside the cell.


Answer: C

The correct folding of proteins is necessary to maintain healthy cells and tissues. Unfolded proteins are responsible for such neurodegenerative disorders as Alzheimer's disease, Huntington's disease, and Creutzfeldt-Jakob disease (the specific faulty protein is different for each disease). What is the ultimate fate of these disease-causing, unfolded proteins?

02:31

The correct folding of proteins is necessary to maintain healthy cells and tissues. Unfolded proteins are responsible for such neurodegenerative disorders as Alzheimer's disease, Huntington's disease, and Creutzfeldt-Jakob disease (the specific faulty protein is different for each disease). What is the ultimate fate of these disease-causing, unfolded proteins?



(a) They are degraded.
(b) They bind a different target protein.
(c) They form structured filaments.
(d) They form protein aggregates.


Answer: D

Protein folding can be studied using a solution of purified protein and a denaturant (urea), a solvent that interferes with noncovalent interactions. Which of the following is observed after the denaturant is removed from the protein solution?

02:31

Protein folding can be studied using a solution of purified protein and a denaturant (urea), a solvent that interferes with noncovalent interactions. Which of the following is observed after the denaturant is removed from the protein solution?



(a) The polypeptide returns to its original conformation.
(b) The polypeptide remains denatured.
(c) The polypeptide forms solid aggregates and precipitates out of solution.
(d) The polypeptide adopts a new, stable conformation.


Answer: A

The sequences for three different tripeptides are written out below. Indicate whether you expect to find them in the inner core or on the surface of a cytosolic protein, and explain your answer.

02:31

The sequences for three different tripeptides are written out below. Indicate whether you expect to find them in the inner core or on the surface of a cytosolic protein, and explain your answer.



A. Serine-Threonine-Tyrosine
B. Alanine-Glycine-Leucine
C. Proline-Serine-Alanine

Which of the following statements is true?

02:30

Which of the following statements is true?



(a) Peptide bonds are the only covalent bonds that can link together two amino acids in proteins.
(b) The polypeptide backbone is free to rotate about each peptide bond.
(c) Nonpolar amino acids tend to be found in the interior of proteins.
(d) The sequence of the atoms in the polypeptide backbone varies between different proteins.


Answer: C

To study how proteins fold, scientists must be able to purify the protein of interest, use solvents to denature the folded protein, and observe the process of refolding at successive time points. What is the effect of the solvents used in the denaturation process?

02:30

To study how proteins fold, scientists must be able to purify the protein of interest, use solvents to denature the folded protein, and observe the process of refolding at successive time points. What is the effect of the solvents used in the denaturation process?



(a) The solvents break all covalent interactions.
(b) The solvents break all noncovalent interactions.
(c) The solvents break some of the noncovalent interactions, resulting in a misfolded protein.
(d) The solvents create a new protein conformation.


Answer: B

Fully folded proteins typically have polar side chains on their surfaces, where electrostatic attractions and hydrogen bonds can form between the polar group on the amino acid and the polar molecules in the solvent. In contrast, some proteins have a polar side chain in their hydrophobic interior. Which of the following would not occur to help accommodate an internal, polar side chain?

02:30

Fully folded proteins typically have polar side chains on their surfaces, where electrostatic attractions and hydrogen bonds can form between the polar group on the amino acid and the polar molecules in the solvent. In contrast, some proteins have a polar side chain in their hydrophobic interior. Which of the following would not occur to help accommodate an internal, polar side chain?



(a) A hydrogen bond forms between two polar side chains.
(b) A hydrogen bond forms between a polar side chain and the protein backbone.
(c) A hydrogen bond forms between a polar side chain and an aromatic side chain.
(d) Hydrogen bonds form between polar side chains and a buried water molecule.


Answer: C

The variations in the physical characteristics between different proteins are influenced by the overall amino acid compositions, but even more important is the unique amino acid ______________.

02:29

The variations in the physical characteristics between different proteins are influenced by the overall amino acid compositions, but even more important is the unique amino acid ______________.



(a) number.
(b) sequence.
(c) bond.
(d) orientation.


Answer: B

Polypeptides are synthesized from amino acid building blocks. The condensation reaction between the growing polypeptide chain and the next amino acid to be added involves the loss of _____.

02:29

Polypeptides are synthesized from amino acid building blocks. The condensation reaction between the growing polypeptide chain and the next amino acid to be added involves the loss of _____.




(a) a water molecule.
(b) an amino group.
(c) a carbon atom.
(d) a carboxylic acid group.


Answer: A

NADH and NADPH are activated carrier molecules that function in completely different metabolic reactions. Both carry two additional ________ and one additional _____________. This combination can also be referred to as a hydride ion.

02:29

NADH and NADPH are activated carrier molecules that function in completely different metabolic reactions. Both carry two additional ________ and one additional _____________. This combination can also be referred to as a hydride ion.



(a) protons, electron.
(b) electrons, phosphate.
(c) hydrogen's, electron.
(d) electrons, proton.

Answer: D

The synthesis of glutamine from glutamic acid requires the production of an activated intermediate followed by a condensation step that completes the process. Both amino acids are shown in Figure Q3-72.In the condensation step, _______________ is displaced by _____.

02:29

The synthesis of glutamine from glutamic acid requires the production of an activated intermediate followed by a condensation step that completes the process. Both amino acids are shown in Figure Q3-72.In the condensation step, _______________ is displaced by _____.



(a) OH, NH3.
(b) ADP, NH2.
(c) ATP, NH3.
(d) phosphate, NH3.


Answer: D

The synthesis of glutamine from glutamic acid requires the production of an activated intermediate followed by a condensation step that completes the process. Both amino acids are shown in Figure Q3-71. Which molecule is added to glutamic acid in the activation step?

02:28

The synthesis of glutamine from glutamic acid requires the production of an activated intermediate followed by a condensation step that completes the process. Both amino acids are shown in Figure Q3-71. Which molecule is added to glutamic acid in the activation step?



(a) phosphate
(b) NH3
(c) ATP
(d) ADP


Answer: A

The anhydride formed between a carboxylic acid and a phosphate (Figure Q3-69A) is a high-energy intermediate for some reactions in which ATP is the energy source. Arsenate can also be incorporated into a similar high-energy intermediate in place of the phosphate (Figure Q3-69B). Figure Q3-69C shows the reaction profiles for the hydrolysis of these two high-energy intermediates. What is the effect of substituting arsenate for phosphate in this reaction?

02:28

The anhydride formed between a carboxylic acid and a phosphate (Figure Q3-69A) is a high-energy intermediate for some reactions in which ATP is the energy source. Arsenate can also be incorporated into a similar high-energy intermediate in place of the phosphate (Figure Q3-69B). Figure Q3-69C shows the reaction profiles for the hydrolysis of these two high-energy intermediates. What is the effect of substituting arsenate for phosphate in this reaction?



(a) It forms a high-energy intermediate of lower energy.
(b) It forms a high-energy intermediate of the same energy.
(c) It decreases the stability of the high-energy intermediate.
(d) It increases the stability of the high-energy intermediate.


Answer: C

You are studying a biochemical pathway that requires ATP as an energy source. To your dismay, the reactions soon stop, partly because the ATP is rapidly used up and partly because an excess of ADP builds up and inhibits the enzymes involved. You are about to give up when the following table from a biochemistry textbook catches your eye.

02:28

You are studying a biochemical pathway that requires ATP as an energy source. To your dismay, the reactions soon stop, partly because the ATP is rapidly used up and partly because an excess of ADP builds up and inhibits the enzymes involved. You are about to give up when the following table from a biochemistry textbook catches your eye.



Figure Q3-68

Which of the following reagents are most likely to revitalize your reaction?


(a) a vast excess of ATP
(b) glucose 6-phosphate and enzyme D
(c) creatine phosphate and enzyme A
(d) pyrophosphate


Answer: C

Energy cannot be created or destroyed, but it can be converted into other types of energy. Cells use potential kinetic energy to generate stored chemical energy in the form of activated carrier molecules, which are often employed to join two molecules together in _____________ reactions.

02:28

Energy cannot be created or destroyed, but it can be converted into other types of energy. Cells use potential kinetic energy to generate stored chemical energy in the form of activated carrier molecules, which are often employed to join two molecules together in _____________ reactions.



(a) oxidation
(b) hydrolysis
(c) condensation
(d) reduction


Answer: C

Activated carriers are small molecules that can diffuse rapidly and be used to drive biosynthetic reactions in the cell. Their energy is stored in a readily transferable form such as high-energy electrons or chemical groups. Which of the molecules below is the most widely used activated carrier?

02:27

Activated carriers are small molecules that can diffuse rapidly and be used to drive biosynthetic reactions in the cell. Their energy is stored in a readily transferable form such as high-energy electrons or chemical groups. Which of the molecules below is the most widely used activated carrier?



(a) FADH2
(b) NADH
(c) NADPH
(d) ATP



Answer: D

The study of enzymes also includes an examination of how the activity is regulated. Molecules that can act as competitive inhibitors for a specific reaction are often similar in shape and size to the enzyme's substrate. Which variable(s) used to describe enzyme activity will remain the same in the presence and absence of a competitive inhibitor?

02:27

The study of enzymes also includes an examination of how the activity is regulated. Molecules that can act as competitive inhibitors for a specific reaction are often similar in shape and size to the enzyme's substrate. Which variable(s) used to describe enzyme activity will remain the same in the presence and absence of a competitive inhibitor?



(a) Vmax
(b) V
(c) Vmax and Km
(d) Km


Answer: A

What information regarding an enzyme-catalyzed reaction is obtained in a plot of the inverse of the initial velocities against the inverse of the corresponding substrate concentrations?

02:27

What information regarding an enzyme-catalyzed reaction is obtained in a plot of the inverse of the initial velocities against the inverse of the corresponding substrate concentrations?



(a) 1/Vmax and 1/Km
(b) 1/V and 1/[S]
(c) Vmax and Km
(d) V and [S]


Answer: A
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