Question

Contraction of a sarcomere, and thus contraction of the muscle as a whole, is accomplished by a cyclic sequence of interactions between actin (thin filaments) and myosin (thick filaments) in the sarcomere. Understanding this sequence of events is essential to understanding the mechanism of muscle contraction at the cellular and molecular levels.

Begin by considering a relaxed muscle. In this state, the myosin molecules of the thick filaments are not in contact with the actin of the thin filaments, and ADP and Pi are bound to the myosin heads. An action potential on the muscle cell plasma membrane initiates contraction of the sarcomeres from this relaxed state.
Rank the following events in the sequence in which they occur, beginning with myosin forming a cross-bridge with actin.
A) Myosin head forms a cross-bridge with actin
B) Myosin releases Pi
C) Myosin pulls actin toward center of sarcomere
D) Myosin binds ATP
E) Cross-bridge between myosin and actin is broken
F) Myosin hydrolyzes ATP to ADP and Pi
G) Myosin head extends.

Answer 1

Muscle contraction starts with the formation of a cross-bridge between myosin and actin. Pi is released, actin is pulled towards the center of the sarcomere, and the cycle continues. Hence the correct answer is option E

Step-by-step explanation:

The sequence of events in muscle contraction begins with the formation of a cross-bridge between the myosin head and actin. This is followed by the release of Pi and the pulling of actin towards the center of the sarcomere by the myosin head. Next, the myosin binds ATP, which leads to the breaking of the cross-bridge between myosin and actin. The myosin head then extends, and the cycle continues.

Hence the correct answer is option E

Answer 2

The correct answer will be-

A) Myosin head forms a cross-bridge with actin

B) Myosin pulls actin toward center of sarcomere

C) Myosin binds ATP

D) Myosin hydrolyzes ATP to ADP and Pi

E) Cross-bridge between myosin and actin is broken

F) Myosin releases Pi

G) Myosin head extends.

Step-by-step explanation:

The sarcomere is the structural and functional unit of the muscle which when contracts and relaxes causes the muscle movement.

The sarcomere is composed of actin and myosin filaments which respond in the presence and absence of calcium ions.

When the calcium ions are present, the myosin head binds the actin. The binding of myosin to actin pulls the thin filament shortening the sarcomere and contraction of the muscle.

The myosin head then attaches the ATP molecule which leads to the detachment of the myosin from the actin. This is followed by the breakdown of the ATP into ADP and Pi by ATPase activity. This allows the myosin head to extend and ready to bind actin again and the cycle continues.