Question

To what does the myosin head bind in order to form a cross bridge?

A)sarcoplasmic reticulum
B)protein complex
C)calcium
D)actin

Answer 1

The myosin head binds to actin to form a cross-bridge, which is facilitated by the presence of calcium ions binding to troponin, leading to muscle contraction.

Step-by-step explanation:

The myosin head binds to actin in order to form a cross bridge during muscle contraction. Actin binding sites are usually covered by a protein called tropomyosin, to which the troponin complex is attached. This complex is sensitive to calcium ions. When calcium binds to troponin, it causes tropomyosin to move away from the actin-binding sites. This exposes the active site on actin, allowing the myosin head to attach, forming a cross-bridge that is critical for muscle contraction. During the power stroke, ADP and inorganic phosphate are released, which bends the myosin head and results in contraction. A new ATP molecule then binds to the myosin head, causing it to detach from actin and allowing the cycle to repeat.

Answer 2

The myosin head binds to actin in order to form a cross bridge.So the correct option is D)actin

Step-by-step explanation:

Muscle contraction is a complex process involving the interaction between two key proteins: myosin and actin. The myosin head, also known as the myosin cross bridge, binds to actin during muscle contraction. This interaction is crucial for the sliding filament theory, where actin filaments slide past myosin filaments, leading to muscle contraction.

The myosin head contains binding sites for both ATP and actin. When calcium ions are released in response to a neural signal, they bind to regulatory sites on actin, exposing binding sites for the myosin heads. The myosin heads then bind to actin, forming cross bridges and allowing the contraction process to proceed.

In the sarcomere, the basic functional unit of a muscle, the myosin heads extend towards the actin filaments. The binding of myosin heads to actin initiates a series of events, including the release of stored energy and the shortening of sarcomeres, leading to muscle contraction. This molecular interaction is essential for muscle function and enables various physiological activities, from simple movements to complex athletic performances.

Understanding the binding of myosin heads to actin provides insights into the fundamental mechanisms of muscle contraction and the regulation of motor activities in the human body.

In summary, the myosin head binds to actin to form a cross bridge, playing a central role in the process of muscle contraction. This interaction is finely regulated and orchestrated by the release of calcium ions and the availability of ATP, ensuring the precise control of muscle movements in response to neural signals.So the correct option is D)actin