The Ig fold can be described as a

The Ig fold can be described as a

A) globular fold composed of a helices.
B) a globular fold composed of a four helix bundle.
C) a globular fold composed of a ß sandwich.
D) a globular fold composed of ß barrel.
E) a coiled-coil.


Answer: C) a globular fold composed of a ß sandwich.

Which statement about antigen-binding sites in antibodies is false?

Which statement about antigen-binding sites in antibodies is false?

A) An antigen-binding site on an IgG is formed by the amino-terminal ~110 amino acids of a light chain and the amino terminal ~110 amino acids of a heavy chain.
B) An antigen-binding site on an IgG is formed by the variable region of a light chain and the variable region of a heavy chain.
C) The antigen-binding site is composed of two Ig folds.
D) Antigen-binding specificity is determined by the sequences of the hypervariable sequences in both the light chain and the heavy chain.
E) Antigen binding specificity is determined exclusively by the sequences in the carboxy- terminal ~110 amino acids in the light chain and the heavy chain.


Answer: E) Antigen binding specificity is determined exclusively by the sequences in the carboxy- terminal ~110 amino acids in the light chain and the heavy chain.

Fab fragments can be generated by

Fab fragments can be generated by

A) reduction of IgG molecules.
B) oxidation of IgG molecules.
C) limited digestion of IgG molecules with papain.
D) combining two light chains.
E) combining two heavy chains.


Answer: C) limited digestion of IgG molecules with papain.

How many antigen-binding sites are present on an IgM molecule?

How many antigen-binding sites are present on an IgM molecule? 

A) 2
B) 4
C) 10
D) 16
E) 25


Answer: C) 10

How many antigen-binding sites are present on an IgG molecule?

How many antigen-binding sites are present on an IgG molecule? 

A) 1
B) 2
C) 3
D) 4
E) 5


Answer: B) 2

Which class of antibodies has been implicated in allergic reactions?

Which class of antibodies has been implicated in allergic reactions?

A) IgA
B) IgD
C) IgE
D) IgG
E) IgM

Answer: C) IgE

IgG is one of five classes of antibodies that can be produced by our immune system. IgGs have a molecular mass of approximately 150 kDa, what is their subunit composition?

IgG is one of five classes of antibodies that can be produced by our immune system. IgGs have a molecular mass of approximately 150 kDa, what is their subunit composition?

A) 2 light chains and 2 heavy chains
B) 2 light chains, 2 heavy chains, and a J chain
C) 4 light chains, 4 heavy chains, and a J chain
D) 6 light chains, 6 heavy chains, and a J chain
E) 10 light chains, 10 heavy chains , and a J chain.


Answer: A) 2 light chains and 2 heavy chains

IgG is the most common immunoglobulin in the circulatory system and in the extravascular fluid. It is composed of two light chains and two heavy chains. What is the approximate molecular mass of an IgG molecule?

IgG is the most common immunoglobulin in the circulatory system and in the extravascular fluid. It is composed of two light chains and two heavy chains. What is the approximate molecular mass of an IgG molecule?

A) 23 kDa
B) 75 kDa
C) 150 kDa
D) 360 kDa
E) 950 kDa


Answer: C) 150 kDa

How many different classes of antibodies are produced by the human immune system?

How many different classes of antibodies are produced by the human immune system? 

A) 1
B) 2
C) 3
D) 4
E) 5


Answer: E) 5

Humoral immunity is mediated by soluble molecules. Which cell type produces the soluble molecules that carry out the humoral immunity?

Humoral immunity is mediated by soluble molecules. Which cell type produces the soluble molecules that carry out the humoral immunity?

A) T cells
B) B cells
C) macrophages
D) neutrophils
E) monocytes


Answer: B) B cells

Treadmilling refers to

Treadmilling refers to

A) myosin heads walking along actin microfilaments.
B) actin and myosin filaments sliding along each other.
C) actin monomers moving through a microfilament from the + end to the - end.
D) synthesis and degradation of actin monomers.
E) the interactions between actin and tropomyosin.


Answer: C) actin monomers moving through a microfilament from the + end to the - end.

Humoral immunity refers to that part of the immune response that is mediated by

Humoral immunity refers to that part of the immune response that is mediated by 

A) T lymphocytes.
B) antibodies.
C) antigens.
D) the thymus.
E) the skin.


Answer: B) antibodies.

Which of the following statements about actin is not true?

Which of the following statements about actin is not true?

A) Actin is the most abundant cytoplasmic protein in many cell types.
B) Actin forms microfilaments in many cell types.
C) Actin plays an important role in endocytosis.
D) Actin is present only as monomers in nonmuscle cells.
E) Actin filaments are dynamic, they grow at one end and they lose subunits at the other end.


Answer: D) Actin is present only as monomers in nonmuscle cells.

Which statement about actin is correct?

Which statement about actin is correct?

A) Actin is expressed only in muscle.
B) Actin is expressed at low levels in most cells.
C) No known function has been described for actin in nonmuscle cells.
D) Nonmuscle cells only contain G actin.
E) Actin is the most abundant cytoplasmic protein in many cell types.


Answer: E) Actin is the most abundant cytoplasmic protein in many cell types.

Muscle contraction is triggered

Muscle contraction is triggered

A) in response to an increase in the cytoplasmic Ca2+ concentration.
B) in response to a decrease in the cytoplasmic Ca2+ concentration.
C) in response to an increase in the cytoplasmic cAMP concentration.
D) in response to a decrease in the cytoplasmic cAMP concentration.
E) in response to an increase in the cytoplasmic titin concentration.


Answer: A) in response to an increase in the cytoplasmic Ca2+ concentration.

During muscle contraction myosin heads

During muscle contraction myosin heads

A) walk along thick filaments toward the M disk.
B) walk along thick filaments toward the Z disk.
C) walk along thin filaments toward the M disk.
D) walk along the thin filaments toward the H zone.
E) walk along the thin filaments toward the Z disk.


Answer: E) walk along the thin filaments toward the Z disk.

The energy needed to drive muscle contraction comes from ATP hydrolysis that is carried out by

The energy needed to drive muscle contraction comes from ATP hydrolysis that is carried out by

A) G-actin.
B) F-actin.
C) myosin heads.
D) myosin tails.
E) tropomyosin.


Answer: C) myosin heads.

Which statement about actin is not true?

Which statement about actin is not true?

A. There are two actin genes, one for F-actin and one for G-actin.
B. Monomeric G-actin polymerizes to form F-actin.
C. Actin filaments are polar (the ends can be distinguished).
D. Actin can bind ATP.
E. Actin is a common protein in nonmuscle cells.


Answer: A. There are two actin genes, one for F-actin and one for G-actin.

Which statement about myosin is not true?

Which statement about myosin is not true? 

A) Myosin is a heterohexamer.
B) Myosin contains two globular heads.
C) Myosin contains six different polypeptides
D) Myosin aggregates to form thick filaments
E) All of the answers above are true of myosin.


Answer: E) All of the answers above are true of myosin.

During muscle contraction

During muscle contraction

A) myosin pulls actin filaments toward the M disk.
B) myosin pushes actin filaments toward the Z disk.
C) actin pulls myosin toward the Z disk.
D) actin pushes myosin toward the M disk.
E) All of the answers above are correct.

Answer: A) myosin pulls actin filaments toward the M disk.