Which two proteins make up the sarcomere?

The sarcomere is the fundamental unit of muscle contraction in striated muscle tissue, and it is primarily composed of two key proteins: actin and myosin. Actin is a thin filament that provides the structural component of the sarcomere and serves as the site for myosin binding during muscle contraction. Myosin, on the other hand, is a thick filament that interacts with actin to produce the force necessary for muscle contraction through a process called the sliding filament theory.

In the sliding filament model, myosin heads bind to actin filaments and pull them toward the center of the sarcomere, resulting in muscle shortening and contraction. This dynamic interaction between actin and myosin is crucial for all voluntary and involuntary muscle movements in the body.

The other options listed include proteins that play different roles in muscle structure and function. Tropomyosin and troponin are regulatory proteins that aid in muscle contraction by controlling the interaction between actin and myosin, but they do not make up the primary structure of the sarcomere itself. Collagen and elastin are more associated with connective tissues rather than muscle contraction. Keratin is involved in forming protective structures like hair and nails and does not play a role in muscle contraction.