Which statement about muscle contraction is correct?

• A. Thick filaments stretch, whereas thin filaments stay the same length.
• B. Thin filaments stretch, whereas thick filaments stay the same length.
• C. A typical muscle fiber at rest contains enough ATP for millions of contractions.
• D. Iron and fats bound to actin play a critical role in muscle cell contraction and relaxation.
• E. Neither thin nor thick filaments change in size, although the area of overlap between them increases.

Answer: (E)

Verified step by step guidance

1. Understand the structure of muscle fibers: Muscle fibers are composed of myofibrils, which contain repeating units called sarcomeres. Sarcomeres are the functional units of muscle contraction and are made up of thick and thin filaments.
2. Identify the components of the filaments: Thick filaments are primarily composed of the protein myosin, while thin filaments are primarily composed of the protein actin, along with troponin and tropomyosin.
3. Learn about the sliding filament theory: During muscle contraction, the sliding filament theory explains that the thick and thin filaments slide past each other, which shortens the sarcomere and leads to muscle contraction.
4. Clarify the role of filament length: According to the sliding filament theory, neither the thick nor the thin filaments change in length during contraction. Instead, the overlap between them increases, shortening the sarcomere.
5. Review the correct statement: The correct statement is that neither thin nor thick filaments change in size, although the area of overlap between them increases during muscle contraction.