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