Which of the following statements regarding the sliding filament model is false?

• A. ATP is required for the detachment of myosin heads from actin filaments.
• B. Calcium ions bind to troponin, causing a conformational change that exposes binding sites on actin.
• C. The length of the actin and myosin filaments changes during contraction.
• D. During muscle contraction, the sarcomere shortens as actin and myosin filaments slide past each other.

Answer: (C)

Verified step by step guidance

1. Understand the sliding filament model: This model explains how muscles contract by the sliding of actin and myosin filaments past each other, leading to the shortening of the sarcomere, the functional unit of muscle fibers.
2. Identify the role of ATP: ATP is crucial for muscle contraction as it provides the energy required for the detachment of myosin heads from actin filaments after a power stroke, allowing the cycle of muscle contraction to continue.
3. Recognize the role of calcium ions: Calcium ions bind to troponin, which causes a conformational change in the troponin-tropomyosin complex, exposing the binding sites on actin for myosin heads to attach and initiate contraction.
4. Clarify the misconception about filament length: During muscle contraction, the length of the actin and myosin filaments does not change. Instead, they slide past each other, which shortens the sarcomere and leads to muscle contraction.
5. Conclude with the false statement: The statement that the length of the actin and myosin filaments changes during contraction is false, as the filaments themselves remain the same length; it is the sarcomere that shortens.