Which of the following is/are true for muscle contraction?

Question

a. active sites on actin become available for binding when calcium binds to tropomyosin
b. active sites on actin are blocked by troponin when a muscle is at rest
c. an isometric contraction has increased muscle fiber tension but no muscle fiber shortening
d. all of these

Answer 1

a is not true, because calcium binds to troponin, not to tropomyosin.
b. is not true, because the myosin-binding site on actin is blocked by tropomyosin, not by troponin.
Thus, c is the only correct answer.

Answer 2

all are correct