Question

What is a cross-bridge?

Answer 1

Answer:

The correct answer is - option C.

Explanation:

Cross bridge is a structure that is globular made up of the actin filaments and activated myosin attachments. The head of the myosin binds to the binding site that is present on the actin filaments that are exposed to the actin molecules.

Due to this structure, the movement in muscle occurs as they contract while attaching temporarily to the actin filament that is present near and exposed.

Thus, the correct answer is - option C.

Answer 2

Answer:

d. the movement of myosin head while attached to actin myofilament

Explanation:

During muscle contraction, the calcium ions released from the sarcoplasmic reticulum in the sarcoplasm bind to troponin which in turn removes tropomyosin from the myosin-binding sites present on the actin. Hydrolysis of ATP at the myosin heads energize them. These myosin heads with stored energy bind to the myosin-binding sites on the actin filaments. In their bound conditions on the actin filaments, myosin heads are called cross bridges. Only one myosin head of a single myosin molecule forms cross-bridge at a time.