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ULTRA STRUCTURE ULTRA STRUCTURE OF MYOFILAMENTSOF MYOFILAMENTS
Actin and Myosin filamentsActin and Myosin filaments
MYOSIN STRUCTUREMYOSIN STRUCTURE Thick filamentThick filament Six polypeptide chainsSix polypeptide chains Two heavy chainsTwo heavy chains Four light chainsFour light chains Two heavy long polypeptide Two heavy long polypeptide
chains coiled togetherchains coiled together Tail of myosin moleculeTail of myosin molecule Heads are called cross Heads are called cross
bridgesbridges Link thick and thin filament Link thick and thin filament
during contractionduring contraction
MYOSIN FILAMENTMYOSIN FILAMENT Myosin filamentMyosin filament Made up of 200 or more myosin moleculesMade up of 200 or more myosin molecules HingeHinge Each cross bridge is flexibleEach cross bridge is flexible ContractionContraction Interaction between cross bridges of myosin and actin Interaction between cross bridges of myosin and actin
filaments filaments Myosin filament is surrounded by six actin filamentsMyosin filament is surrounded by six actin filaments
ULTRASTRUCTURE OF ACTIN ULTRASTRUCTURE OF ACTIN FILAMENTFILAMENT
Thin filamentThin filament ActinActin Two chains coiled around Two chains coiled around
each othereach other TropomyosinTropomyosin Two strands of another Two strands of another
protein, tropomyosin protein, tropomyosin twisting around actin twisting around actin chains chains
TroponinTroponin
Three polypeptide complexThree polypeptide complex
One binds to actinOne binds to actin
Second binds to Second binds to tropomyosintropomyosin
Third binds to CaThird binds to Ca
ACTINACTIN Back bone of actin filament is F actinBack bone of actin filament is F actin Each strand of actin is composed of G actin Each strand of actin is composed of G actin
moleculesmolecules To each G actin molecule, one molecule of To each G actin molecule, one molecule of
ADPADP Binding sitesBinding sites
Titin moleculeTitin molecule
TITINTITIN
FunctionsFunctions Keeps the myosin and actin filaments in placeKeeps the myosin and actin filaments in place Large filamentous moleculesLarge filamentous molecules Act as a frameworkAct as a framework Springy in natureSpringy in nature About 3 million molecular weightAbout 3 million molecular weight Largest protein molecule in the bodyLargest protein molecule in the body
Molecular mechanism of muscle Molecular mechanism of muscle contractioncontraction
Sliding filament modelSliding filament model Presented by H. Huxley and F. HuxleyPresented by H. Huxley and F. Huxley Shifting of actin and myosin filamentsShifting of actin and myosin filaments Actin filaments slide pass each otherActin filaments slide pass each other Reduction in length of I-bandReduction in length of I-band Z-line come acrossZ-line come across Disappearance of H-zoneDisappearance of H-zone
What causes actin filaments to slide What causes actin filaments to slide inward?inward?
Forces generated by interaction of cross bridges from myosin Forces generated by interaction of cross bridges from myosin with actin filamentswith actin filaments
Under resting condition forces remain inactiveUnder resting condition forces remain inactive Action potentialAction potential Reaches at neuro-muscular junctionReaches at neuro-muscular junction Motor neuronsMotor neurons T-tubuleT-tubule T systemT system TriadTriad Srcoplasmic reticulumSrcoplasmic reticulum Opening of Calcium gatesOpening of Calcium gates
Motor unitsMotor units
What causes actin filaments to slide What causes actin filaments to slide inward?inward?
Release of calcium into cytosolRelease of calcium into cytosol((the aqueous component of the cytoplasm of a cell, within which various organelles and particles are suspended).
Binding of calcium to troponinBinding of calcium to troponin Binding sites open Binding sites open Cross bridges attachesCross bridges attaches Contraction initiatesContraction initiates ATP comes from mitochondriaATP comes from mitochondria All or none principleAll or none principle
CROSS BRIDGESCROSS BRIDGES
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