Final answer:
The function of cross-bridges in muscle contraction is to connect myosin filaments to actin filaments, facilitating the sliding movement that leads to the muscle shortening and contracting.
Step-by-step explanation:
The function of cross-bridges in muscle contraction is to connect myosin filaments to actin filaments. This connection is crucial for the process of muscle contraction, as outlined in the following steps:
- Calcium ions (Ca++) binding to troponin cause the exposure of the active sites on actin filaments.
- Myosin heads bind to these exposed actin-binding sites, forming a cross-bridge.
- During the power stroke, the myosin heads pivot, pulling the actin filaments towards the center of the sarcomere.
- ATP binds to the myosin head, causing the cross-bridge to detach.
- Hydrolysis of ATP relocks the myosin head, preparing it for another cycle of cross-bridge formation and movement.
This series of events known as the cross-bridge cycle is a process by which the actin and myosin filaments slide past each other, leading to the shortening of the muscle fiber and muscle contraction. ATP is necessary for cross-bridge formation and the sliding of filaments, and it is the energy source for this entire process.