biochemistry of muscle

8/12/2019 Biochemistry of Muscle

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Faculty of Dentistry, Hang Tuah University

2013

ian Mulawarmanti


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Body movement (Locomotion) Maintenance of posture Respiration

Diaphragm and intercostal contractions Communication (Verbal and Facial) Constriction of organs and vessels

Peristalsis of intestinal tract

Vasoconstriction of b.v. and other structures (pupils)

Heart beat Production of body heat (Thermogenesis)


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1.. Smooth Muscle 2. SKELETAL Muscle 3. Cardiac Muscle

walls of most viscera, usually attached to bones wall of heartblood vessels, skin under conscious control not under conscious

controlnot under conscious striated control striatednot striated


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structure control nuclei Location

skeletal striated Primarilyvoluntary

Multiplephripheral

Attachedto bone

cardiac striated Involuntary

Nervus &

endocrine

1 rarely2 Centrally

located

Heart wall

smooth Non

striated

Involuntary

Nervus &

endocrine

Centrally

located

Walls of

hollow

organ


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Other protein

components ofmuscle fibrils


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sarcolemmasacroplasmsarcoplasmicreticulum

transverse tubuletriad

cisternae of sarcoplasmicreticulumtransverse tubule

myofibrilactinfilamentsmyosinfilamentssarcomere


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As a monomer, termed G-Actin, at low ionicstrength and can bind one ATP

At physiological ionic strength (plus Mg2+), the G-actin forms fibrous polymers termed F-actin. ATPhydrolysis occurs during this process and ADPremains bound to each F-actin subunit

F-actin is the core of the thin filament, and eachmonomer is capable of binding one myosinglobular head. The coil repeats at roughly everyseventh actin unit.


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Thick Filamentscomposed of myosincross-bridges

Thin Filamentscomposed of actinassociated withtroponinand

tropomyosin


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also known as myoneuraljunctionsite where an axonandmuscle fiber meet

motor neuronmotor end platesynapse

synaptic cleftsynaptic vesiclesneurotransmitters


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When sarcomeresshorten, thick and thin

filaments slide past oneanother

H zones and I bandsnarrowZ lines move closertogether


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muscle impulses causesarcoplasmic reticulum torelease calcium ions intocytosol

calcium binds totroponin to change itsshapeposition of tropomyosin

is alteredbinding sites on actinare exposedactin and myosinmolecules bind


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myosin cross-bridge attachesto actin binding site

myosin cross-bridge pullsthin filament

ADP and phosphatereleased from myosin

new ATP binds tomyosin

linkage between actinand myosin cross-bridgebreak

ATP splits

myosin cross-bridge goes back

to original position


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acetylcholinesteraserapidly decomposes Ach remaining in the

synapse

muscle impulse stops

stimulus to sarcolemma and muscle fiber membrane ceases

calcium moves back into sarcoplasmic reticulum

myosin and actin binding prevented

muscle fiber relaxes


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The contractile process

The pumpingof calcium back into thesarcoplasmic reticulumduring relaxation

Maintaining the sodium/potassium iongradients across the sarcolema(membranepotential)


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Phosphocreatine

Glycolysis from Glycogen or Glucose Tricarboxylic acid cycle (TCA or Krebs

cycle)

Electron transport chain


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It is also known as creatine phosphate orPcr, that is an important energy stored in

the skeletal muscle. Creatineis synthesized in the liver (from

Arg, Gly, Met), and transported to themuscle cells, where it is phosphorylated bycreatine kinase (ATP is required) to creatinephosphate.


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ADP+

Phosphocreatine

Creatine Kinase

ATP+

Creatine


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This reaction occurs in the sarcoplasm.ATP broken down during contraction is

rapidly restored.Phosphocreatine is subject to

depletion during extended periods ofcontraction (intense effort).

Rephosphorylation of creatine occursat the mitochondrial membrane.


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It is the sequence of reactions that converts

glucose pyruvate

with the concomitant production of a

relatively small amount of ATP


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Glycogen is a polysaccharide of glucose(Glc) which functions as the primary short

term energy storage in muscle cells(myofiber).

Glycogen is found in the form of granules inthe sarcoplasm, and plays an importantrole in the glucose cycle.


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Glycogen

GlycogenPhosphorylase

Glucose 1-Phosphate

Glucose 6-phosphate


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Summary

1 Glucose + 2ADP + 2Pi +2NAD

2 Pyruvate + 2ATP + 2NADH +2H + 2H2O


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It is also known as Citric Acid Cycle

Krebs cycle.

It is a series of enzyme-catalyzed chemicalreactions of central importance in all livingcells that use oxygen as part of cellularrespiration.


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TCA cycle


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SummaryPyruvate

1ATP + 4NADH +1FADH + 3CO2


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It is a chemical reaction between anelectron donor (such as NADH) and an

electron acceptor (such as O2) to thetransfer of H+ions across a membrane

These H+ions are used to produceATP, asthey move back across the membrane.


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Summary NADH

NAD + 3ATP + 4H2O


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Process Direct product FinalATP

GLYCOLYSIS 2 NADH

2ATP

4 or 6

2

Pyruvate oxidation(two per glucose)

2 NADH(mitochondrial matrix)

6

Acetyl-CoA oxidation 6 NADH(mitochondrial matrix)

2 FADH22 ATP

184

2

Total yield per molecule of glucose


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Release of Ca2+

through voltage-or Ca2+-sensitivechannel activatescontraction

Pumps inducerelaxation


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Ca2+Channels and Pumps

Release of Ca2+from the SR triggers

contraction Reuptake of Ca2+into SR relaxes muscle So how is calcium released in response to

nerve impulses? Answer has come from studies of antagonistmolecules that block Ca2+channel activity


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At rest tropomyosin blocks

the myosin binding sites on

actin.

When calciumbinds to thetroponin complex aconformational change

results in the movement of

the tropomyosintropinincomplex and exposure of

actinsmyosin binding sites.


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Follow the actionpotential

When an actionpotential meets themuscle cells

sarcoplasmic

reticulum (SR)stored Ca2+ is

released.


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An individual muscle cell either contractscompletely or not all.

Individual muscles, composed of manyindividual muscle fibers, can contract tovarying degrees.

One way variation is accomplished by varying

the frequency of action potentials reach themuscle from a single motor neuron.


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Graded musclecontraction can also

be controlled by

regulating thenumber ofmotor units involved

in the contraction


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Recruitment of motor neurons increasesthe number of muscle cells involved in acontraction

Some muscles, such as those involved inposture, are always at least partially

contracted

Fatigue is avoided by rotating among motorunits


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In addition to skeletal muscle, vertebrateshave cardiac and smooth muscle

Cardiac muscle: similar to skeletal muscle Intercalated discs facilitate the coordinated

contraction of cardiac muscle cells. Can generate there own action potentials. Action potentials of long duration.


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Smooth muscle: lacks the striations seen in bothskeletal and cardiac muscle

Contracts with less tension, but over a greaterrange of lengths, than skeletal muscle. No T tubules and no SR Ca2+ enters the cytosol from via the plasma

membrane. Slow contractions, with more control over

contraction strength than with skeletal muscle. Found lining the walls of hollow organs


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12/02/2008 Biochemistry: MusclesPage 50

of 46

No troponin complex in smooth muscle

Ca2+activates myosin light chain kinase(MLCK) which phosphorylates LC2, theregulatory light chain of myosin

Ca2+

effect is via calmodulin - a cousin ofTroponin C


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Hormones regulate contraction -epinephrine, a smooth muscle relaxer,

activates adenylyl cyclase, making cAMP,which activates protein kinase, whichphosphorylates MLCK, inactivating MLCKand relaxing muscle


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creatine phosphate stores energy that quickly converts

ADP to ATP

1) Creatine phosphate 2) Cellular respiration


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Anaerobic Phaseglycolysisoccurs in cytoplasmproduces little ATP

Aerobic Phasecitric acid cycleelectron transport chainoccurs in themitochondriaproduces most ATPmyoglobinstores extraoxygen


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Muscle tissue has two sources of oxygen. diffuses in from the blood

released by myoglobin inside muscle fibers

Aerobic system requires O2 to produce ATPneeded for prolonged activity increased breathing effort during exercise

Recovery oxygen uptake elevated oxygen use after exercise (oxygen debt)

lactic acid is converted back to pyruvic acid

elevated body temperature means all reactions

faster


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oxygen not availableglycolysis continuespyruvic acid convertedto lactic acid

liver converts lacticacid to glucose

Oxygen debtamount of oxygen needed by liver cells to use the accumulatedlactic acid to produce glucose


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by-product of cellular respiration

muscle cells are major source of body heat

blood transports heat throughout body


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Slow oxidative (slow-twitch)

red in color (lots of mitochondria, myoglobin & blood vessels)

prolonged, sustained contractions for maintaining posture Fast oxidative-glycolytic (fast-twitch A)

red in color (lots of mitochondria, myoglobin & blood vessels)

split ATP at very fast rate; used for walking and sprinting

Fast glycolytic (fast-twitch B) white in color (few mitochondria & Blood Vessel, low myoglobin)

anaerobic movements for short duration; used for weight-lifting

(angkat berat)


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These differences are due primarily to themale sex hormone testosterone

With more muscle mass, men are generallystronger than women

Body strength per unit muscle mass,however, is the same in both sexes


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With age, connective tissue increases and musclefibers decrease

Muscles become stringier and more sinewy By age 80, 50% of muscle mass is lost (sarcopenia) Decreased density of capillaries in muscle Reduced stamina Increased recovery time Regular exercise reverses sarcopenia


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Inability to contractdepletion of creatine phosphate

decline of Ca+2 within the sarcoplasm

Commonly caused fromdecreased blood flowinsufficient oxygen or glycogen

Ion imbalances across the sarcolemma

Accumulation of lactic acidinsufficient release of acetylcholine from motor neurons

Cramp sustained, involuntary muscle contraction


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biochemistry of muscle

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