Interaction of thick & thin filaments __________________ –_____________________________________ _____________________________________ –_____________________________________

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Interaction of thick & thin filaments__________________ __________________________________________________________________________ _____________________________________


Where is ATP needed?

3412111Cleaving ATP ADP allows myosin head to bind to actin filamentthin filament(actin)thick filament(myosin)ATPmyosin headbinding site

So thats where those10,000,000 ATPs go!Well, not all of it!ADPformcrossbridgereleasecrossbridgeshortensarcomere12Closer look at muscle cell

multi-nucleatedMitochondrionSarcoplasmicreticulumTransverse tubules(T-tubules)3

Muscle cell organelles_________________________ muscle cell cytoplasmcontains many mitochondria_________________________organelle similar to ERnetwork of tubes_________________Ca2+ released from SR through channelsCa2+ restored to SR by Ca2+ pumpspump Ca2+ from cytosolpumps use ATPCa2+ ATPase of SRATP

The restof theATPs!But whatdoes theCa2+ do?4Muscle at restInteracting proteinsat rest, ________ molecules hold _____________ fibers so that they cover the myosin-binding sites on actintroponin has Ca2+ binding sites

5The Trigger: motor neurons

Motor neuron triggers muscle contractionrelease ______________ (Ach) neurotransmitter6Nerve signal travels down ___________stimulates sarcoplasmic reticulum (SR) of muscle cell to ________________ flooding muscle fibers with Ca2+ Nerve trigger of muscle action

7At rest, tropomyosin _______ myosin-binding sites on actinsecured by troponinCa2+ binds to _______________________ causes movement of troponinreleasing tropomyosin_____________________________ on actinCa2+ triggers muscle action

8Coupling 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.

How Ca2+ controls muscle__________________exposed actin binds to myosinfibers slide past each otherratchet systemshorten muscle cellmuscle contractionmuscle doesnt relax until Ca2+ is pumped back into SR requires ATP


Fig. 50-27-4ThinfilamentsATP Myosin head (low-energy configurationThick filamentThin filamentThickfilamentActinMyosin head (high-energy configurationMyosin binding sitesADPP iCross-bridgeADPP iMyosin head (low-energy configurationThin filament movestoward center of sarcomere.ATP ADPP i+11

Fig. 50-28Myosin-binding siteTropomyosin(a) Myosin-binding sites blocked(b) Myosin-binding sites exposedCa2+Ca2+-binding sitesTroponin complexActin__________ concentration: muscle contracts________ concentration: binding sites are covered and contraction stopsRole of Ca andRegulatory Proteins12

Put it all together1ATP234576ATP13How it all worksAction potential causes ______ release from SRCa2+ binds to ______________Troponin moves ____________ uncovering ___________________ on actinMyosin binds ______uses ____ to "ratchet" each timereleases, "unratchets" & binds to next actinMyosin pulls actin chain alongSarcomere _________Z discs move closer togetherWhole fiber shortens _____________!Ca2+ pumps restore Ca2+ to SR ___________!pumps use _____ATPATP14

Fig. 50-26ZRelaxedmuscleM Z Fully contractedmuscleContractingmuscleSarcomere0.5 mContractedSarcomere15