Question

The hydrolysis of ATP causes myosin to immediately (Select one): a. bind more tightly to the actin (rigor). b. rotate into a position (cocked) to bind to actin. c. swivel, moving the actin molecule. d. release from the actin. e. release ADP.

Answer 1

The hydrolysis of ATP causes myosin to release from the actin, after which myosin adopts a cocked position due to ATPase activity, setting the stage for the next cycle of muscle contraction.

Step-by-step explanation:

The hydrolysis of ATP causes myosin to immediately release from the actin. This detachment occurs when ATP binds to the myosin head, prompting the release of already bound ADP and Pi and causing the myosin to detach from the actin filament. Following this, ATP is hydrolyzed to ADP and inorganic phosphate, P1, a reaction catalyzed by the enzyme ATPase found on the myosin. The energy from this hydrolysis induces a conformational change in the myosin head, transitioning it into a cocked position with potential energy stored for the next cycle of muscle contraction. If the actin binding sites are not obscured, a cross-bridge can form, signifying that the myosin head can span the distance to the actin and prepare for the next power stroke.

Answer 2

b. Rotate into a position (cocked) to bind to actin.

Step-by-step explanation:

The cycle starts with the myosin strongly united to the actin (in absence of ATP). The union of ATP dissociates the myosin from the actin and the ATP hydrolysis induces a conformational change in the myosin. This change affects the neck region of the myosin, which acts like a lever arm displacing the head group of the myosin. The ADP and phosphate stay united to the myosin head, which unites to the actin filament in a new position, liberating the phosphate and releasing ADP. This way, the myosin head adopts again its initial conformation.