Overview
This lecture explains how myosin and actin proteins, together with ATP, generate mechanical motion, forming the basis of muscle contraction.
Myosin and Actin Structure
- Myosin II consists of two protein strands twisted together, forming heads that interact with actin.
- Actin is a filamentous protein that serves as a track for myosin movement.
- Myosin functions as an ATPase enzyme, meaning it hydrolyzes ATP.
Steps in Myosin-Actin Interaction Cycle
- Step 1: ATP binds to the myosin head, causing myosin to detach from the actin filament.
- Step 2: ATP is hydrolyzed to ADP and a phosphate, releasing energy that "cocks" the myosin head into a high-energy state.
- Step 3: The phosphate group is released, triggering the power stroke where myosin pushes against actin, creating mechanical movement.
- Step 4: ADP is released, resetting the myosin head to its original position, but one step further along the actin filament.
Conversion of Energy
- The cycle converts chemical energy from ATP into mechanical energy used for movement.
- Structural changes in myosin, driven by ATP binding and hydrolysis, enable force generation.
Key Terms & Definitions
- Myosin — A motor protein that interacts with actin to generate force.
- Actin — A protein filament serving as a track for myosin movement.
- ATPase — An enzyme that catalyzes the hydrolysis of ATP to ADP and phosphate.
- Power Stroke — The action of myosin pushing on actin, leading to muscle contraction.
- Conformation — The shape or structure of a protein, which changes during the contraction cycle.
Action Items / Next Steps
- Prepare for upcoming material on how nerves stimulate muscle contraction.
- Review the steps of the myosin-actin cycle for understanding muscle mechanics.