Question

Myosin head separates from actin when?
A. ATP hydrolysis.
B. When ATP attaches to myosin head.
C. When ATP releases from myosin head.
D. When ATP releases from Actin.

Answer 1

Hint: Every myosin molecule consists of a knob-like head structure, a stretchable neck region, and a one tail region. The head region of myosin consists of two binding sites, one is for the ATP and other is for actin molecule. The thin filament (i.e., blue filament) is made up of two threads of actin which overlains with tropomyosin and troponin.

Complete answer:
The theory that is called the sliding filament theory is the theory that describes the step by step procedure of muscle contraction constructed on muscle proteins that slides each other to generate a muscle movement.

According to the sliding filament theory, the myosin filaments (a thick molecule) of the fibres of muscles slide on the actin filament (a thin molecule) in the mechanism of muscle contraction. In this process of muscle contraction the two groups of filaments (i.e., actin and myosin) always remain at a more or less constant length.

 Myosin molecule has one other binding site for binding of ATP, where enzymatic activity hydrolyzes ATP to form ADP molecule; this conversion releases a phosphate molecule (inorganic) plus energy.
Binding of ATP causes myosin to release action, permit actin and myosin filaments to detach from each other.

The attachment of myosin head and actin filaments with the products of ATP hydrolysis executes and initiates a power stroke associated with release of hydrolysis products, and this makes detachment from actin filaments on binding with the newly formed ATP. Further, this detached myosin filament head hydrolyses ATP, and restores its starting position.

Hence, the correct answer is (B) 'When ATP attaches to myosin head'.

Note:
The binding of ATP results in the release of actin, in this way it allows actin and myosin to become detached from each other. The enzyme that is present at the binding site of myosin is known as ATPase. Thus, the ATP hydrolysis releases the energy that changes the angle of the head of myosin as a “cocked” shaped position.