Question 1

Which of the following best describes the role of ATP in the actin-myosin cycle of muscle contraction?

Accepted Answer

ATP binding to myosin causes dissociation of myosin from actin, allowing the cycle to continue.

Question 2

What is the primary effect of the resonance structure of a peptide bond in proteins?

Accepted Answer

It creates a partial double bond character, restricting rotation around the C–N bond.

Question 3

During the actin-myosin cycle, what event immediately follows the hydrolysis of ATP by myosin?

Accepted Answer

Myosin head moves into a 'high-energy' conformation, ready to bind actin.

Question 4

Which statement best explains why the peptide bond is planar?

Accepted Answer

The resonance between the carbonyl and amide nitrogen creates partial double bond character, restricting rotation.

Question 5

If an enzyme-catalyzed reaction is compared to the same reaction without the enzyme, what is the most likely effect of the enzyme?

Accepted Answer

The enzyme lowers the activation energy, increasing the reaction rate.

Question 6

Which of the following best defines a 'cofactor' in enzymatic reactions?

Accepted Answer

A non-protein chemical compound required for enzyme activity, which can be organic or inorganic.

Question 7

In the actin-myosin cycle, what is the consequence if ADP is not released from myosin after the power stroke?

Accepted Answer

Myosin will remain tightly bound to actin, preventing further cycles.

Question 8

Which of the following statements about enzyme cofactors is correct?

Accepted Answer

Cofactors can be either organic molecules (coenzymes) or inorganic ions.

Question 9

A mutation causes the myosin head to lose its ability to hydrolyze ATP. What is the most likely effect on muscle contraction?

Accepted Answer

The myosin head will not enter the high-energy conformation, preventing contraction.

Question 10

Which of the following best describes the 'power stroke' in muscle contraction?

Accepted Answer

The conformational change in myosin that pulls the actin filament after Pi is released.

Question 11

Which of the following is a direct result of the partial double bond character of the peptide bond?

Accepted Answer

Restricted rotation around the C–N bond.

Question 12

If the resonance structure of the peptide bond did not exist, what would be the most likely consequence for protein structure?

Accepted Answer

Proteins would have increased flexibility due to free rotation around the C–N bond.

Question 13

Which of the following best explains why ATP is necessary for muscle relaxation?

Accepted Answer

ATP binding to myosin causes myosin to release from actin, allowing relaxation.

Question 14

Which of the following is NOT a function of a coenzyme?

Accepted Answer

Providing structural support to the enzyme's active site.

Question 15

A patient is diagnosed with a genetic disorder that prevents the release of ADP from myosin after the power stroke. What is the most likely clinical symptom?

Accepted Answer

Continuous muscle contraction (rigor).

Question 16

Which of the following best describes the chemical structure of a peptide bond?

Accepted Answer

A bond between the carboxyl group of one amino acid and the amino group of another, with partial double bond character.

Question 17

Which of the following statements about the actin-myosin cycle is correct?

Accepted Answer

ATP binding to myosin causes it to detach from actin.

Question 18

Which of the following best explains why enzymes do not alter the equilibrium constant ($$K_{eq}) of a $$reaction?

Accepted Answer

Enzymes increase both the forward and reverse reaction rates equally, so the ratio of products to reactants at equilibrium remains unchanged.

Question 19

A researcher adds a non-hydrolyzable analog of ATP to a muscle fiber preparation. What is the most likely effect on the actin-myosin cycle?

Accepted Answer

Myosin will detach from actin upon ATP analog binding but will not perform the power stroke.

Biochemistry Study Notes: Muscle Contraction, Peptide Bond Resonance, and Enzyme Cofactors

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