Which proteins primarily make up skeletal muscle?

• A. Collagen and elastin.
• B. Actin and myosin.
• C. Myoglobin and hemoglobin.
• D. Fibronectin and laminin.

Answer: (B)

Actin and myosin form the core contractile machinery of skeletal muscle. Inside each muscle fiber, the repeating units called sarcomeres contain thick filaments made of myosin and thin filaments made of actin. The myosin heads form cross-bridges with actin and, using energy from ATP, pull the actin filaments past one another to shorten the sarcomere and produce contraction. This interaction is the fundamental mechanism by which skeletal muscle generates force.

Other proteins mentioned—collagen and elastin, fibronectin and laminin, myoglobin, and hemoglobin—have important roles in tissue support, connectivity, or oxygen transport, but they are not the primary components that make up the contractile muscle fibers.