actin and myosin interaction

physiology of muscle contraction

1. ACTIN AND MYOSIN INTERACTION PRESENTED BY : MUHAMMAD NABEEL Roll no. 62

2. MOLECULAR MECHANISM OF MUSCLE CONTRACTION Sliding filament mechanism Mechanical forces generated by interaction of myosin cross bridges with actin filaments cause the actin filaments to slide inward among the myosin filaments.

3. Under resting conditions these forces are inhibited. When an action potential travels over the muscle fiber membrane the sarcoplasmic reticulum releases large quantities of calcium ions. Forces between myosin and actin filaments are activated and contraction begins.

4. MYOSIN FILAMENT Composed of multiple myosin molecules. The tails of myosin molecules bundle together to form the body of the filament. Cross bridges. ATPase enzyme

5. THE ACTIN FILAMENT Each actin filament is made up of actin , tropomyosin and troponin .

6. Interaction of one myosin filament with two actin filaments and calcium ions causes contraction

7. INHIBITION OF ACTIVE SITES Active sites on actin filament are inhibited by the troponin - tropomyosin complex. ACTIVATION BY Ca++ IONS Ca++ ions combine with troponin causing the troponin complex to tug on the tropomyosin molecule. Active sites uncovered allowing contraction to proceed.

8. WALK ALONG THEORY Myosin head attaches to an active site, Head tilts automatically toward the arm that is dragging along the actin filament which is called power stroke. Immediately after tilting the head automatically breaks away from the active site and returns to its normal perpendicular direction. In this position, it combines with a new active site farther along the actin filament and pulls the ends of the actin filaments towards the centre of the myosin filament.

9. CYCLE OF MUSCLE CONTRACTION (WALK ALONG THEORY)

10. CONTRACTION IN SMOOTH MUSCLE

11. ACTIVATION OF MYOSIN IN SMOOTH MUSCLE