Question

Calcium is important in skeletal muscle contraction because it
A) Detaches the myosin head from the actin filament.
B) Binds to troponin to remove the masking of active sites on actin for myosin.
C) prevents the formation of bonds between the myosin cross-bridge and the actin filament.
D) Activates the myosin ATPase binding to it.

Answer 1

Hint: During muscle contraction the thick filament slides over the fine filaments and in the process hydrolysis of ATP occurs. This entire process happens in a sequential manner. It is regulated by an ion which is produced in the sarcoplasmic reticulum.

Complete answer:
Muscle contraction does not always mean muscle shortening because muscle tension can be generated without modification in the length of the muscle, for e.g. when lifting a large book or a dumbbell at the same poster. Muscle contraction begins with an impulse that travels along the axon and gets to the neuromuscular junction or motor endplate. As a result, acetylcholine is secreted into the synaptic cleft and an action potential is generated on the sarcolemma.
The formation of this action potential releases calcium ions from the sarcoplasmic reticulum within the sarcoplasm. The increase in calcium ions inside the sarcoplasm causes the activation of actin sites. Calcium ions stick to the troponin on actin filaments and eliminate the troponin wrapped all over actin filaments. Therefore, active action sites are uncovered which enables myosin heads to link to this site. After muscle contraction, the myosin heads pull the actin filament and frees ADP along with inorganic phosphate. ATP molecules bind and separate myosin and the cross Bridge are damaged. Skeletal muscle contraction is regulated by calcium ions. These calcium ions bind to the protein complex and remove the masking of the active sites. This results in the exposure of active binding sites acting for myosin.
Thus, the correct answer is option C.

Note: There are four types of muscle contraction:
i. Isometric: A muscular contraction in which the length of the muscle does not change.
ii. Isotonic: A muscular contraction in which the length of the muscle changes.
iii. Eccentric: An isotonic contraction where the muscle lengthens.
iv. Concentric: An isotonic contraction where the muscle shortens.