Overview
This lecture explains how the proteins myosin and actin, in combination with ATP, work together to produce mechanical motion in cells, forming the basis of muscle contraction.
Actin and Myosin Structure
- Myosin II consists of two protein strands wound around each other with globular heads.
- Actin is a filamentous protein that serves as a track for myosin movement.
Myosin-Actin Interaction Cycle
- Step 1: ATP binds to the myosin head, causing myosin to release from actin.
- Step 2: ATP is hydrolyzed into ADP and a phosphate group, releasing energy and cocking myosin into a high-energy state.
- Step 3: The phosphate group is released from myosin, triggering the "power stroke" that pushes on actin and produces movement.
- Step 4: ADP is released from myosin, returning it to its original state, ready to start the cycle again further along the actin filament.
Energy Conversion
- ATP provides the chemical energy to change myosin's shape and position via bond hydrolysis.
- The protein changes conformation (shape) during each step, with some conformations storing more energy.
- This process converts chemical energy (ATP) into mechanical energy (movement).
Key Terms & Definitions
- Myosin — motor protein that interacts with actin and uses ATP energy to generate movement.
- Actin — filamentous protein that provides a track along which myosin moves.
- ATP (Adenosine Triphosphate) — molecule that stores and provides energy for cellular processes.
- ATPase — enzyme that hydrolyzes ATP, such as myosin.
- Power stroke — the action phase where myosin pushes actin, causing mechanical movement.
- Conformation — the specific three-dimensional shape of a protein.
Action Items / Next Steps
- Review diagrams of the myosin-actin ATPase cycle.
- Prepare for the next lecture on how nerve stimulation triggers muscle contraction.