Archive for October 2018

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)...

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...

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...

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...

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,...

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...

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...

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...

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...

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...

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'...

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...

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...

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...

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...

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...

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...

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...

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...

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....

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...

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...

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...

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....

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...

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...

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,...

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...

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...

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...

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...

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...

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,...

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...

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...

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...

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...

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...

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...

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...
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