You have designed a drug that is supposed to bind to the myosin binding sites on actin. You inject it into a relaxed muscle, but find that none of the drug bound. Which of the following explains why?

A) There are no myosin binding sites on actin.

B) Troponin molecules are covering myosin-binding sites on actin.

C) The myosin binding sites are covered by ATP.

D) The myosin binding sites on actin are covered by tropomyosin.

E) None of the choices is correct

D) The myosin binding sites on actin are covered by tropomyosin

Explanation:

The muscle contraction and relaxation involves the myofilaments which physically contract and relax.

However, the physical contraction and relaxation are controlled by the other protein molecules called tropomyosin and troponin molecules.

The muscle contracts when a cross-bridge is formed between the myosin and actin but myosin binds actin only when myosin-binding site on actin is free of tropomyosin which usually covers in a relaxed state.

In the given question, when the drug is not ab; e to bind to the myosin-binding site therefore to shows that the myosin binding site is covered by the tropomyosin.

Thus, Option-D is the correct answer.