What are the proteins involved in muscle contraction within a sarcomere?

The proteins involved in muscle contraction within a sarcomere are actin and myosin. These two proteins play a critical role in the sliding filament theory of muscle contraction.

Actin is a thin filament that provides a track along which myosin, which is a thick filament, moves to generate force and shorten the muscle. During contraction, myosin heads attach to binding sites on the actin filaments to form cross-bridges. The myosin heads then pivot, pulling the actin filaments closer together and producing the contraction of the muscle. This process is powered by ATP, which is essential for breaking the cross-bridge and allowing myosin to re-cock and bind again.

The other proteins mentioned, such as collagen and elastin, are primarily structural proteins found in connective tissues and are not directly involved in muscle contraction. Keratin and albumin serve different functions, where keratin is a structural protein in hair and nails, and albumin is a protein found in blood plasma. Fibrin is involved in blood clotting, while casein is a milk protein. None of these play a role in the actual mechanism of muscle contraction within a sarcomere.