Which statement is correct about a muscle contraction?
ATP causes fascicles to contract muscle fibers.
Sarcomeres produce actin and myosin.
Myosin heads attach to sites on actin filaments.
Myofibrils attach to Z lines.
The correct statement about a muscle contraction is: "Myosin heads attach to sites on actin filaments."
To understand why this statement is correct, let's break it down:
Muscle contractions are initiated by the interaction between two proteins: actin and myosin. Actin is a thin filament, while myosin is a thick filament. Within a muscle, these filaments are organized in repeating structures called sarcomeres. Sarcomeres are the basic functional units of muscle contractions.
During a muscle contraction, myosin heads, located on the thick filaments, attach to specific binding sites on the actin filaments. This attachment allows the myosin heads to pull the actin filaments, causing the sarcomere to shorten. This process is known as cross-bridge cycling. ATP (adenosine triphosphate) provides the energy for this interaction by binding to the myosin heads and allowing them to detach from the actin filaments.
So, out of the given statements, the correct one is that myosin heads attach to sites on actin filaments during a muscle contraction.