Question

required information
at rest, the active sites on actin molecules are covered by ________ and ________, two contractile proteins that inhibit contraction.
multiple choice
actin and myosin
sarcoplasmic reticulum and terminal cisternae
troponin and tropomyosin
sarcolemma and sarcoplasm

Explanation:

Troponin and tropomyosin are regulatory proteins in muscle contraction. At rest, tropomyosin covers the active - sites on actin molecules, and troponin is associated with tropomyosin. Actin and myosin are the main contractile proteins, and the other options refer to other muscle - related structures or components not related to covering actin active sites at rest.

Answer:

C. Troponin and tropomyosin