Question

multiple select question

select all that apply

what are two contractile proteins found in a myofibril?

myosin
troponin
actin
tropomyosin

Explanation:

Define contractile proteins

In muscle physiology, myofibrils contain different types of proteins categorized by function. Contractile Proteins are those that do the actual work of shortening the muscle fiber by sliding past one another. The two primary contractile proteins are actin and myosin.

Identify myosin function

Myosin Structure makes up the thick filaments of the sarcomere. The myosin heads bind to actin to form cross-bridges, using ATP to pull the thin filaments and generate muscle tension. Therefore, myosin is a contractile protein.

Identify actin function

Actin is the main component of the thin filaments. It contains the active binding sites where myosin heads attach during contraction. Because actin directly interacts with myosin to produce force, it is the second contractile protein.

Analyze regulatory proteins

Troponin Function and Tropomyosin Regulation are critical for controlling muscle contraction, but they do not generate force themselves. Instead, they act as regulatory proteins. Tropomyosin blocks the active sites on actin when the muscle is at rest, and troponin binds calcium ions to shift tropomyosin out of the way, allowing contraction to begin. Thus, troponin and tropomyosin are classified as regulatory, not contractile, proteins.

Answer:

• Myosin (Correct answer)
• Troponin
• Actin (Correct answer)
• Tropomyosin