1. The Ig fold can be described as a
   A
   Option A: a coiled-coil.
   B
   Option B: a globular fold composed of β barrel.
   C
   Option C: globular fold composed of α helices.
   D
   Option D: a globular fold composed of a four helix bundle.
   E
   Option E: a globular fold composed of a β sandwich.

Option E: a globular fold composed of a β sandwich.

2. How many antigen-binding sites are present on an IgM molecule?
   A
   Option A: 25
   B
   Option B: 10
   C
   Option C: 4
   D
   Option D: 16
   E
   Option E: 2

Option B: 10

3. How many antigen-binding sites are present on an IgG molecule?
   A
   Option A: 1
   B
   Option B: 4
   C
   Option C: 2
   D
   Option D: 3
   E
   Option E: 5

Option C: 2

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

Option A: 2 light chains and 2 heavy chains

5. How many different classes of antibodies are produced by the human immune system?
   A
   Option A: 1
   B
   Option B: 2
   C
   Option C: 4
   D
   Option D: 3
   E
   Option E: 5

Option E: 5

6. Humoral immunity refers to that part of the immune response that is mediated by
   A
   Option A: antigens.
   B
   Option B: the thymus.
   C
   Option C: T lymphocytes.
   D
   Option D: antibodies.
   E
   Option E: the skin.

Option D: antibodies.

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

Option D: actin monomers moving through a microfilament from the (+) end to the (-) end.

8. Which of the following statements about actin is not true?
   A
   Option A: Actin is present only as monomers in nonmuscle cells.
   B
   Option B: Actin filaments are dynamic, they grow at one end and they lose subunits at the other end.
   C
   Option C: Actin forms microfilaments in many cell types.
   D
   Option D: Actin is the most abundant cytoplasmic protein in many cell types.
   E
   Option E: Actin plays an important role in endocytosis.

Option A: Actin is present only as monomers in nonmuscle cells.

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

Option B: Actin is the most abundant cytoplasmic protein in many cell types.

10. Muscle contraction is triggered
    A
    Option A: in response to an increase in the cytoplasmic cAMP concentration.
    B
    Option B: in response to an increase in the cytoplasmic Ca2+ concentration.
    C
    Option C: in response to an increase in the cytoplasmic titin concentration.
    D
    Option D: in response to a decrease in the cytoplasmic cAMP concentration.
    E
    Option E: in response to a decrease in the cytoplasmic Ca2+ concentration.

Option B: in response to an increase in the cytoplasmic Ca2+ concentration.