In skeletal muscle contraction, which molecule directly supplies the energy used by myosin heads during the cross-bridge cycle?

• A. ATP
• B. Lactic acid
• C. Glycogen
• D. Creatine

Answer: (A)

Verified step by step guidance

1. Understand the role of the myosin head in the cross-bridge cycle during skeletal muscle contraction. The myosin head binds to actin filaments and performs a power stroke to generate force.
2. Recognize that energy is required for the myosin head to detach from actin and re-cock for another cycle. This energy comes from the hydrolysis of a specific molecule.
3. Identify that ATP (adenosine triphosphate) is the molecule that directly provides energy by being hydrolyzed into ADP and inorganic phosphate, releasing energy used by the myosin head.
4. Note that other molecules like lactic acid, glycogen, and creatine play different roles: lactic acid is a byproduct of anaerobic metabolism, glycogen is a stored form of glucose, and creatine helps regenerate ATP but does not directly supply energy to the myosin head.
5. Conclude that ATP is the direct energy source for the myosin heads during the cross-bridge cycle in skeletal muscle contraction.