Interaction of thick & thin filaments

1. sarcomere sarcomere Interaction of thick & thin filaments • __________________ • __________________________________________________________________________ • _____________________________________

2. Where is ATP needed? binding site CleavingATP ADP allows myosin head to bind to actin filament thin filament(actin) myosin head ADP thick filament(myosin) 1 2 ATP So that’s where those10,000,000 ATPs go! Well, not all of it! formcrossbridge 1 1 3 1 releasecrossbridge shortensarcomere 1 4

3. Closer look at muscle cell Sarcoplasmicreticulum Transverse tubules(T-tubules) Mitochondrion multi-nucleated

4. Muscle cell organelles Ca2+ ATPase of SR • _________________________ • muscle cell cytoplasm • contains many mitochondria • _________________________ • organelle similar to ER • network of tubes • _________________ • Ca2+ released from SR through channels • Ca2+ restored to SR by Ca2+ pumps • pump Ca2+ from cytosol • pumps use ATP The restof theATPs! But whatdoes theCa2+ do? ATP

5. Muscle at rest • Interacting proteins • at rest, ________ molecules hold _____________ fibers so that they cover the myosin-binding sites on actin • troponin has Ca2+ binding sites

6. The Trigger: motor neurons • Motor neuron triggers muscle contraction • release ______________ (Ach) neurotransmitter

7. Nerve trigger of muscle action • Nerve signal travels down ___________ • stimulates sarcoplasmic reticulum (SR) of muscle cell to ________________ • flooding muscle fibers with Ca2+

8. Ca2+ triggers muscle action • At rest, tropomyosin _______ myosin-binding sites on actin • secured by troponin • Ca2+ binds to ________ • _______________causes movement of troponin • releasing tropomyosin • _____________________________ on actin

9. Coupling Excitation to Contraction 1. Ca2+ ____ action potentials to contraction. 2. At rest, Ca2+ is stored in the __________. 3. Spaced along the plasma membrane (_____________) of the muscle fiber are inpocketings of the membrane that form ________ of the “__________". These tubules plunge repeatedly into the interior of the fiber. 4.The tubules of the T system terminate near the ___________________ of the sarcoplasmic reticulum. 5. Each action potential created at the neuromuscular junction sweeps quickly along the sarcolemma and is carried into the T system.

10. How Ca2+ controls muscle • __________________ • exposed actin binds to myosin • fibers slide past each other • ratchet system • shorten muscle cell • muscle contraction • muscle doesn’t relax until Ca2+ is pumped back into SR • requires ATP ATP ATP

11. Thick filament Thinfilaments Thin filament Myosin head (low-energy configuration ATP Fig. 50-27-4 ATP Thickfilament Myosin binding sites Thin filament movestoward center of sarcomere. Actin ADP Myosin head (low-energy configuration Myosin head (high-energy configuration P i ADP ADP + P i Cross-bridge P i

12. Role of Ca and Regulatory Proteins Ca2+-binding sites Tropomyosin Actin Troponin complex Fig. 50-28 (a) Myosin-binding sites blocked ________ concentration: binding sites are covered and contraction stops __________ concentration: muscle contracts Ca2+ Myosin-binding site (b) Myosin-binding sites exposed

13. Put it all together… 1 2 3 ATP 7 4 6 ATP 5

14. How it all works… • Action potential causes ______ release from SR • Ca2+ binds to ______________ • Troponin moves ____________ uncovering ___________________ on actin • Myosin binds ______ • uses ____ to "ratchet" each time • releases, "unratchets" & binds to next actin • Myosin pulls actin chain along • Sarcomere _________ • Z discs move closer together • Whole fiber shortens  _____________! • Ca2+ pumps restore Ca2+ to SR ___________! • pumps use _____ ATP ATP

15. Sarcomere 0.5 µm M Z Z Fig. 50-26 Relaxedmuscle Contractingmuscle Fully contractedmuscle ContractedSarcomere