Question 1

Which of the following best describes what happens to the A band and I band during skeletal muscle contraction according to the sliding filament model?

Accepted Answer

The I band shortens while the A band remains the same.

Question 2

During the cross-bridge cycle in skeletal muscle contraction, what is the immediate consequence of ATP binding to myosin?

Accepted Answer

Myosin detaches from actin.

Question 3

Which of the following steps in the muscle contraction cycle directly requires the hydrolysis of ATP?

Accepted Answer

Re-cocking of the myosin head.

Question 4

A patient is exposed to a toxin that prevents the reuptake of Ca$$^{2+}$$ into the sarcoplasmic reticulum. Which of the following would most likely occur?

Accepted Answer

Muscle contraction would be prolonged due to sustained high cytosolic Ca$$^{2+}$$ levels.

Question 5

Which of the following best explains why rigor mortis occurs after death?

Accepted Answer

ATP is no longer produced, so myosin cannot detach from actin.

Question 6

Which of the following is the correct sequence of events during skeletal muscle contraction?

Accepted Answer

ATP binds to myosin $$\rightarrow$$ Myosin detaches from actin $$\rightarrow$$ ATP hydrolysis re-cocks myosin head $$\rightarrow$$ Myosin binds to actin $$\rightarrow$$ Power stroke

Question 7

Which of the following statements about the role of Ca$$^{2+} in $$muscle contraction is correct?

Accepted Answer

Ca$$^{2+}$$ binds to troponin, causing a conformational change that exposes myosin-binding sites on actin.

Question 8

If a mutation caused the troponin complex to lose its ability to bind Ca$$^{2+}$$, what would be the most likely effect on muscle contraction?

Accepted Answer

Muscle contraction would be inhibited because myosin-binding sites on actin would remain blocked.

Question 9

Which of the following best describes the role of ATP in the relaxation of skeletal muscle?

Accepted Answer

ATP is required to pump Ca$$^{2+}$$ back into the sarcoplasmic reticulum.

Question 10

A drug inhibits the ATPase activity of myosin. Which step in the muscle contraction cycle would be directly affected?

Accepted Answer

The re-cocking of the myosin head after detachment from actin.

Question 11

Which of the following is true regarding the conformational changes in actin and myosin during muscle contraction?

Accepted Answer

The conformational change in myosin is triggered by the hydrolysis of ATP.

Question 12

Which of the following best explains why the H zone disappears during maximal muscle contraction?

Accepted Answer

The thin filaments slide inward, overlapping the thick filaments and eliminating the H zone.

Question 13

Which of the following would most likely occur if the sarcoplasmic reticulum failed to reabsorb Ca$$^{2+}$$ after contraction?

Accepted Answer

The muscle would remain contracted due to continued exposure of myosin-binding sites on actin.

Question 14

Which of the following is the primary function of the troponin-tropomyosin complex in skeletal muscle?

Accepted Answer

To regulate the exposure of myosin-binding sites on actin in response to Ca$$^{2+}$$ levels.

Question 15

A muscle cell is treated with a compound that prevents the dissociation of Ca$$^{2+}$$ from troponin. What is the most likely outcome?

Accepted Answer

The muscle would remain in a contracted state.

Question 16

Which of the following best describes the relationship between ATP hydrolysis and the power stroke in muscle contraction?

Accepted Answer

ATP hydrolysis re-cocks the myosin head, storing energy for the power stroke.

Biochemistry of Skeletal Muscle Contraction: Sliding Filament Model and ATPase Cycle

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