MECHANISM AND MECHANISM AND CHEMICAL CHANGES CHEMICAL CHANGES DURING MUSCLE DURING MUSCLE CONTRACTIONCONTRACTION

By Deepika of B.Sc final year

Myofibril

A Band ,I band

H zone

Z line

Sarcomere

Muscle proteins – contractile property

2 essential proteins are involved

Actin and Myosin

MYOSIN

Assembled myosin filament

Light meromyosin

Heavy Meromyosin

Head –

ATPase active site, actin binding site

ACTIN

Assembled actin filament

F – actin , G – actin

Tropomyosin

Troponin – 3

TN – I – inhibitory protein

TN – C - Site of Ca attachment

TN – T – Prevents bridges between actin and myosin

SLIDING FILAMENT MECHANISM OF MUSCLE CONTRACTION

Huxley and Hanson

1. 2 sets of filaments

2. Thin filaments slide over thick filaments

3. There is no change in A band

I band and H zone dec or disappear

SERIES OF EVENTS IN CONTRACTION

Step 1 : Depolarization of sarcolemma

Step 2 : Release of Ca ions

Step 3 : Conformational changes in actin

Step 4 : Formation of Actomyosin complex

Step 5 : Interaction of thick and thin

filaments

• Power stroke

Ratchet mechanism

Walk along mechanism

ROLE OF CALCIUM

Ca

Troponin

Tropomyosin

Actin

Myosin

CHEMICAL CHANGES DURING MUSCLE CONTRACTION

ATP utilization

• Polymerization of G-action to F-actin

G-actin + ATP F-actin + ADP + iP

• Formation and dissociation of Actomyosin

Actin + Myosin Actomyosin

ATP ADP

ATPase

REPHOSPHORYLATION OF ATP

1.Phosphagen

Creatine phosphate

Creatine phosphate + ADP ATP + Creatine

2 .Breakdown of muscle carbohydrate

Lactic acid formation

Muscle fatigue

Oxygen debt

Cori cycle

4/5th of lactic acid = glycogen

1/5th of lactic acid = water + Carbondioxide

Thanku…….