MCAT Biology Question 154: Answer and Explanation

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Question: 154

4. With which of the following molecules does Ca²⁺ bind after its release from the sarcoplasmic reticulum to regulate muscle contraction?

A. Myosin
B. Actin
C. Troponin
D. Tropomyosin

Correct Answer: C

Explanation:

Calcium is released from the sarcoplasmic reticulum into the sarcoplasm. It binds the troponin molecules on the thin filaments, causing the strands of tropomyosin to shift, thereby exposing the myosin-binding sites on the filaments.

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