Download MBBS Physiology Presentations 67 Molecular Mechanism of Muscle Contraction Lecture Notes

Download MBBS (Bachelor of Medicine, Bachelor of Surgery) 1st Year, 2nd Year, 3rd Year and Final year Physiology 67 Molecular Mechanism of Muscle Contraction PPT-Powerpoint Presentations and lecture notes

Molecular mechanism of muscle

contraction

Molecularmechanismofmuscle

contraction

? Mostacceptedtheoryatpresent"

Slidingfilamenttheory"

? Proposesthatamuscleshortensorlengthens

becausethemyofibrillarfilamentsslidepasteach
otherwithoutactuallychangingtheirlength.

? Themolecularmotortodrivethisshortening

processistheactionoftheoftheMyosincross
bridges,whichcyclicallybindorattach,rotateand
detachfromtheactinfilamentswithenergy
providedbyATPhydrolysis.


Sliding Filament Theory

I Sliding Filament Theory

Calcium

Actin Filament

Myosin

ATP

Filament

ADP

+ P
Slidingfilamenttheory

Whenmuscleisintherelaxedstate

? Caionconc.inthecytosolislow.
? Atthispointactinandmyosinfilamentsliealong

eachotherinthesarcomere.

? TheMyosinheadatthispointisinahighenergy

condition"cockedup"withADPandinorganic
phosphateboundtoit

? ActivesitesontheGactinmoleculesarecovered

bythetroponintropomyosincomplex.

II Sliding Filament Theory

Actin Filament

Myosin

ADP

Filament

+ P

Myosin head

cocked up
Slidingfilamenttheory

? ActionpotentialsintheTtubulecausetherelease

ofCaionsfromSRintothemusclecytosol

? CabindsTroponinC.Aconformationalchangeis

inducedintheTroponinweakensthethebond
betweenitandActin.

? Thisallowstropomyosintomovelaterallyand

exposetheactivesitesonGActin.

? Thecockedupmyosinmoleculerapidlybindstothe

Actin:thislinkisa"crossbridge"

III Sliding Filament Theory

Calcium binds to Actin

ADP

+ P
IV Sliding Filament Theory

Calcium opens binding sites

V. Sliding Filament Theory

Cross bridge forms,

Connecting Myosin to Actin
Sliding Filament Theory

? Myosin head then undergoes a

conformational change causing a "rachet

action" and pulls the actin filament to the

centre of the sarcomere.

? ADP and Pi are released by this process
? This is called the "power stroke" which

causes the sliding action

VI. Sliding Filament Theory

Conformational Changes

Myosin head: Actin Moves~

"power stroke"

Release of ADP+P
Slidingfilamenttheory

? AnATPbindstotheActomyosincomplex
? Thiscausestheaffinityofmyosinforactin

todecrease

? Themyosinheadchangesitspositionto

closearoundtheATPandhydrolyzeit.

? ThischangeinconformationoftheMyosin

headreleasesthemyosinfromtheactin.

VII. Sliding Filament Theory

New ATP binds
IX. Sliding Filament Theory

ATP hydrolysed

ADP

Myosin returns to cocked

+ P

up position

Fresh cycle starts

Slidingfilamenttheory

? CyclingcontinuesuntilcytosolicCalevels

remainhigh

? OneCaionreleasesoneTroponinwhich

covers7activesites.

? Allmyosinmoleculesdonotmove

simultaneouslybutsequentiallylikeoarsona
boatandcausethemyosinslidealongthe
Actinfilament
Muscle relaxed

Calcium pumped out of cytosol: active sites covered

ADP

+ P

Muscleenergetics

?

EnergycurrencyformusclecontractionisATP

?

HydrolysisofATPbyMyosinATPaseenergizescross
bridgespriortocycling.

?

BindingofATPtomyosindissociatescrossbridgesbound
toactinallowingthebridgestorepeattheircycleof
activity.

?

HydrolysisofATPbyCa?ATPaseprovidesenergyfor
activetransportofCaintosarcoplasmicreticulumthus
endingthecontractionandallowingthemusclefiberto
relax.
Rigor mortis

? A condition of the muscles seen after

death

? ATP not available

? Cycle stops at the point of formation of

actomyosin complexes

? "permanent actomyosin" complexes

formed

? Leads to a state of rigor

? Ends with denaturation of protiens