Deck 7: Protein Function and Evolution

Question 1

The most critical substance in stimulating muscle contraction is:

A) ATP.
B) Ca2+.
C) tropomyosin.
D) troponin C.
E) troponin T.

Answer 1

B

Question 2

Which of the following statements about muscle contraction is TRUE?

A) ATP hydrolysis releases myosin from actin.
B) ATP hydrolysis results in strong binding of myosin to actin.
C) ATP hydrolysis causes a conformational change in the myosin head.
D) Muscle contraction occurs as ATP is hydrolyzed.
E) ATP hydrolysis must occur before the actin-binding site closes.

Answer 2

C

Question 3

Comparison of globin sequences from many different species suggests that myoglobin and hemoglobin have evolved from a single myoglobin-like protein.

Answer 3

True

Question 4

The heavy chain of the muscle form of myosin:

A) forms a coiled-coil structure with a globular head domain.
B) contains the motor domain within the C-terminal region.
C) is a complex of 540 kDa.
D) binds ATP near the C-termini.
E) has two covalently bound light chains.

Question 5

The immunoglobulin domain is a stable scaffold containing two antiparallel β- sheets upon which to display hypervariable loops.

Question 6

Both myoglobin and hemoglobin exhibit cooperative binding to oxygen.

Question 7

The specific interaction between an antibody and antigen occurs by virtue of both shape and ________ complementarity.

Question 8

The concentration of Ca2+ in the myoplasm can increase as much as 10,000 fold in response to a motor nerve impulse.

Question 9

The A band of skeletal muscle is formed by noncovalent cross-bridges between the thin filaments that are mainly ________ and the thick filaments that are mainly ________.

Question 10

The ________ binding of oxygen to hemoglobin is facilitated by changes in protein conformation upon oxygen binding to one subunit that affect the binding of oxygen to another subunit.

Question 11

Which of the following observations helps to explain the conformational changes that occur in hemoglobin upon binding to oxygen?

A) The four heme groups are positioned close to the surface of the molecule.
B) An αβ dimer rotates and slides with respect to the other dimer upon binding oxygen.
C) Neither the heme nor the iron ion in the deoxy conformation is in a planar conformation.
D) All of the above
E) B and C

Question 12

The greatest conformational change in the neck piece of myosin occurs during ATP hydrolysis.

Question 13

Which of the following statements is FALSE?

A) Myoglobin is a single polypeptide chain folded about a heme prosthetic group.
B) Hemoglobin is a tetramer, each of which binds a heme group.
C) In both hemoglobin and myoglobin, iron is chelated by a tetrapyrole ring system.
D) The iron in both hemoglobin and myoglobin has two coordination sites that bind to oxygen.
E) Hydrogen bonding to a histidine residue assists stabilization of the Fe2+ -O2 complex in both hemoglobin and myoglobin.

Question 14

The sickle cell mutation causes oxyhemoglobin molecules to ________ due to hydrophobic interactions because a glutamate residue is replaced with a valine.

Question 15

Fetal hemoglobin has a higher affinity for oxygen than does maternal hemoglobin because it has a higher affinity for the allosteric regulator 2,3-bisphosphoglycerate.

Question 16

The production of carbon dioxide during respiration in aerobic tissues lowers the pH in erythrocytes, which in turn ________ the affinity of oxygen binding to hemoglobin.

Question 17

F-actin is a polymer of G-actin monomers and exhibits symmetry.

Question 18

The conserved residues in the hemoglobins and myoglobins include the ________ proximal and distal to the heme iron.

Question 19

Which of the following is NOT true of immunoglobulin molecules?

A) They consist of four polypeptide chains held together by disulphide bridges.
B) They have two identical heavy chains and two identical light chains.
C) Antigenic determinants reside only in the variable region of the light chains.
D) Proteolytic cleavage can generate fragments containing the antigen-binding site.
E) Some are membrane bound.

Question 20

Calcium regulates muscle contraction by binding to:

A) actin.
B) myosin.
C) tropomyosin.
D) troponin C.
E) troponin T.

Question 21

Enzyme-linked immunosorbent assay, western blotting and immunofluorescent light microscopy all make use of the specific interaction between an antigen and an ________.

Question 22

Antibodies cannot be used to purify proteins because the antibody-antigen interaction is too strong.