Q: Which of the following equations correctly represents the reaction catalyzed by creatine kinase during rapid ATP regeneration in skeletal muscle?

$$\text{Creatine phosphate} + \text{ADP} \rightarrow \text{Creatine} + \text{ATP}$$

Question 1

Which of the following best describes the role of calcium ions ($$Ca^{2+}) in $$skeletal muscle contraction?

Accepted Answer

Calcium ions bind to troponin, causing a conformational change that exposes myosin-binding sites on actin.

Question 2

During the crossbridge cycle, what is the immediate consequence of ATP binding to the myosin head?

Accepted Answer

The myosin head detaches from actin.

Question 3

A patient is experiencing muscle rigidity several hours after death. Which of the following best explains this phenomenon (rigor mortis)?

Accepted Answer

ATP is depleted, preventing the detachment of myosin heads from actin.

Question 4

Which process is responsible for the removal of $$Ca^{2+}$$ from the sarcoplasm to end muscle contraction?

Accepted Answer

Active transport of $$Ca^{2+}$$ into the sarcoplasmic reticulum by the $$Ca^{2+}-$$ATPase pump.

Question 5

Which of the following equations correctly represents the reaction catalyzed by creatine kinase during rapid ATP regeneration in skeletal muscle?

Accepted Answer

$$	ext{Creatine phosphate} + 	ext{ADP} ightarrow 	ext{Creatine} + 	ext{ATP}$$

Question 6

A muscle fiber is unable to relax after contraction. Which of the following is the most likely cause?

Accepted Answer

Failure of the $$Ca^{2+}-$$ATPase pump in the sarcoplasmic reticulum.

Question 7

Which of the following best describes the sequence of events in excitation-contraction coupling in skeletal muscle?

Accepted Answer

Action potential in the muscle fiber → release of $$Ca^{2+}$$ from the sarcoplasmic reticulum → binding of $$Ca^{2+} to $$troponin → crossbridge cycling.

Question 8

During intense exercise, which metabolic pathway provides the fastest source of ATP for skeletal muscle contraction?

Accepted Answer

Phosphocreatine breakdown.

Question 9

Which of the following statements about the sliding filament theory is correct?

Accepted Answer

Myosin heads pull actin filaments toward the center of the sarcomere, shortening the muscle.

Question 10

A muscle cell is deprived of oxygen but continues to contract. Which pathway is primarily responsible for ATP production under these conditions?

Accepted Answer

Anaerobic glycolysis converting glucose to lactate.

Question 11

Which of the following best explains why ATP is required for both contraction and relaxation of skeletal muscle?

Accepted Answer

ATP is required to detach myosin from actin and to power the $$Ca^{2+}-$$ATPase pump for relaxation.

Question 12

Which of the following is a direct result of the hydrolysis of ATP by the myosin head during the crossbridge cycle?

Accepted Answer

The myosin head pivots into a cocked, high-energy state.

Question 13

Which of the following best describes the fate of pyruvate during anaerobic metabolism in skeletal muscle?

Accepted Answer

Pyruvate is converted to lactate.

Question 14

A mutation impairs the function of troponin in skeletal muscle. Which of the following would most likely occur?

Accepted Answer

Tropomyosin would continuously block myosin-binding sites on actin, preventing contraction.

Question 15

Which of the following best explains why muscle fibers store glycogen?

Accepted Answer

Glycogen provides a rapid source of glucose for ATP production during muscle activity.

Question 16

Which of the following is the correct order of events in the crossbridge cycle?

Accepted Answer

ATP binds to myosin → myosin detaches from actin → ATP is hydrolyzed → myosin binds to new actin site → power stroke occurs → ADP is released.

Question 17

During moderate, sustained exercise, which source provides the majority of ATP for muscle contraction?

Accepted Answer

Aerobic metabolism of glucose and fatty acids.

Question 18

Which of the following best explains the latent period observed between the action potential and the onset of muscle contraction?

Accepted Answer

It is the time required for $$Ca^{2+}$$ release and binding to troponin.

Question 19

A drug inhibits the function of the sarcoplasmic reticulum $$Ca^{2+}-$$ATPase (SERCA) pump. What is the most likely effect on muscle contraction?

Accepted Answer

Muscle contraction will be prolonged due to delayed $$Ca^{2+}$$ removal.

Question 20

Which of the following best describes the role of mitochondria in skeletal muscle fibers during prolonged exercise?

Accepted Answer

Mitochondria produce ATP through aerobic metabolism, using oxygen to generate energy for sustained contraction.

M#3 Muscle Contraction and ATP Supply in Skeletal Muscle

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