Question 1

The most critical substance in stimulating muscle contraction is:
A) ATP.
B) Ca2+.
C) tropomyosin.
D) troponin C.
E) troponin T.

Accepted Answer

Calcium ions (Ca2+) are the key substance that initiates muscle contraction by binding to troponin C, which causes tropomyosin to shift and allow myosin to bind to actin. While ATP is necessary for muscle contraction, it is not the most critical substance as the myosin/actin cross-bridge cycle can continue without it for a short time. Troponin T is not directly involved in muscle contraction, but instead is part of the troponin complex that binds to tropomyosin and helps regulate muscle contraction.

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.

Accepted Answer

ATP hydrolysis causes a conformational change in the myosin head, which allows it to bind to actin and initiate muscle contraction. This conformational change is important for the swinging of the myosin head, which pulls the actin filament and shortens the muscle fiber. ATP hydrolysis also provides energy to power this movement of myosin.

Question 3

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

Accepted Answer

Analysis of globin sequences from various species has provided evidence that hemoglobin and myoglobin have evolved from a common ancestral myoglobin-like protein. This is supported by similarities in their protein structures and function.

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.

Accepted Answer

The heavy chain of the muscle form of myosin forms a coiled-coil structure with a globular head domain.

Answer: E 
 The heavy chain of the muscle form of myosin 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.

Accepted Answer

This statement is true. The immunoglobulin domain is a structural motif that is found in many proteins, including antibodies. It is composed of two β-sheets, each made up of multiple β-strands, arranged in an antiparallel manner. The loops connecting the β-strands are known as hypervariable loops, and these are where the antigen-binding specificity of the protein is typically found. The immunoglobulin domain is a stable and versatile scaffold for displaying these loops, allowing for a diverse range of binding specificities to be generated.

Question 6

Both myoglobin and hemoglobin exhibit cooperative binding to oxygen.

Accepted Answer

Only hemoglobin exhibits cooperative binding to oxygen, while myoglobin does not; myoglobin has a hyperbolic oxygen binding curve, indicating it does not exhibit cooperativity.

Question 7

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

Accepted Answer

The answer of The specific interaction between an antibody and...

Question 8

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

Accepted Answer

The release of Ca2+ from the sarcoplasmic reticulum in response to a motor nerve impulse can increase the concentration of Ca2+ in the myoplasm by as much as 10,000 fold, allowing for muscle contraction to occur.

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 ________.

Accepted Answer

The answer of The A band of skeletal muscle is...

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.

Accepted Answer

The answer of The ________ binding of oxygen to hemoglobin...

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

Accepted Answer

The observation that the αβ dimer slides and rotates with respect to the other dimer upon binding oxygen explains the overall conformational change in hemoglobin. The observation that neither the heme nor the iron ion in the deoxy conformation is in a planar conformation helps to explain the specific changes that occur within the heme groups upon binding oxygen. The fact that the four heme groups are positioned close to the surface of the molecule is not directly related to the conformational changes that occur upon binding oxygen.

Question 12

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

Accepted Answer

The greatest conformational change in the neck piece of myosin occurs during the release of inorganic phosphate (Pi) from the myosin head after ATP hydrolysis, not during ATP hydrolysis itself. This change is crucial for the power stroke in muscle contraction.

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.

Accepted Answer

The iron in both hemoglobin and myoglobin has six coordination sites, four of which are occupied by the tetrapyrole ring system, one by a histidine residue, and one by oxygen or other ligands.

Question 14

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

Accepted Answer

The answer of The sickle cell mutation causes oxyhemoglobin molecules...

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.

Accepted Answer

Fetal hemoglobin has a higher affinity for oxygen than maternal hemoglobin due to structural differences in the globin protein subunits. Fetal hemoglobin has two gamma subunits, which bind oxygen more tightly than the beta subunits found in adult hemoglobin. The presence of 2,3-bisphosphoglycerate (2,3-BPG) actually decreases the affinity of hemoglobin for oxygen, rather than increasing it. This is because 2,3-BPG binds to a specific site on the beta subunits and stabilizes the T-state conformation, which has a lower affinity for oxygen. Fetal hemoglobin has lower levels of 2,3-BPG, which allows it to bind oxygen more tightly.

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.

Accepted Answer

The answer of The production of carbon dioxide during respiration...

Question 17

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

Accepted Answer

F-actin is a polymer of G-actin monomers, but it exhibits polarity, not symmetry, with distinct plus and minus ends.

Question 18

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

Accepted Answer

The answer of The conserved residues in the hemoglobins and...

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.

Accepted Answer

Antigenic determinants, or epitopes, can reside in both the variable regions of the light and heavy chains of an immunoglobulin molecule.

Question 20

Calcium regulates muscle contraction by binding to:
A) actin.
B) myosin.
C) tropomyosin.
D) troponin C.
E) troponin T.

Accepted Answer

Calcium binds to troponin C, causing a conformational change in the troponin-tropomyosin complex, which allows myosin to bind to actin and initiate muscle contraction. Calcium does not directly bind to actin, myosin, or tropomyosin. Troponin T is a subunit of the troponin complex but does not directly bind calcium.

Quiz 7: Protein Function and Evolution

The most critical substance in stimulating muscle contraction is:

Which of the following statements about muscle contraction is TRUE?

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

The heavy chain of the muscle form of myosin:

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

Both myoglobin and hemoglobin exhibit cooperative binding to oxygen.

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

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

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 .

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.

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

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

Which of the following statements is FALSE?

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

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.

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.

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

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

Which of the following is NOT true of immunoglobulin molecules?

Calcium regulates muscle contraction by binding to: