What are the two components of a sarcomere?

The two components of a sarcomere, actin and myosin, are essential proteins involved in muscle contraction. A sarcomere is the fundamental unit of striated muscle tissue, and it is where the actual muscle contraction happens. Actin is a thin filament, while myosin is a thick filament. During muscle contraction, myosin heads attach to binding sites on the actin filaments, pulling them toward the center of the sarcomere, which shortens the muscle fiber and generates force. This sliding filament model of contraction is central to how muscles function.

The other options focus on proteins that either serve different functions in the body or are part of other bodily structures. Tropomyosin and troponin are regulatory proteins that are also involved in muscle contraction but are not the primary components making up the sarcomere itself. Collagen and elastin are proteins found in connective tissues and provide structural support rather than direct muscle contraction functions. Fibrin and keratin serve roles in coagulation and structural support in skin and hair, respectively, but do not relate to the sarcomere structure. Therefore, highlighting actin and myosin as the core components recognizes their direct role in the mechanics of muscle tissue.