In the context of the sliding filament theory, what protein primarily composes the thin myofilaments within a skeletal muscle sarcomere?

• A. Myosin
• B. Actin
• C. Titin
• D. Troponin

Answer: (B)

Verified step by step guidance

1. Understand that the sliding filament theory explains muscle contraction by the interaction between thick and thin myofilaments within the sarcomere, the basic contractile unit of skeletal muscle.
2. Recall that thick myofilaments are primarily composed of the protein myosin, which has heads that bind to thin filaments during contraction.
3. Identify that thin myofilaments are mainly composed of the protein actin, which provides the binding sites for myosin heads to attach and generate contraction.
4. Recognize that other proteins like troponin and tropomyosin are also part of the thin filament complex but serve regulatory roles rather than being the primary structural protein.
5. Conclude that within the thin myofilaments of a skeletal muscle sarcomere, actin is the primary protein responsible for forming the filament structure.