This document summarizes the mechanism and chemical changes that occur during muscle contraction. It describes the structure of the sarcomere including the myofibrils, bands, and essential contractile proteins actin and myosin. The sliding filament mechanism is explained whereby calcium release allows the myosin heads to bind to actin and pull the thin filaments inward through a power stroke, shortening the sarcomere and causing muscle contraction. Key chemical events include the utilization of ATP to polymerize G-actin to F-actin and for the binding of actomyosin, with ATP hydrolysis providing energy for the power stroke. ATP is then rephosphorylated through phosphagen and carbohydrate breakdown pathways to allow for repeated contractions.

1. MECHANISM ANDMECHANISM AND
CHEMICAL CHANGESCHEMICAL CHANGES
DURING MUSCLEDURING MUSCLE
CONTRACTIONCONTRACTION
By Deepika of B.Sc final year

2. Myofibril
A Band ,I band
H zone
Z line
Sarcomere
Muscle proteins –
contractile property
2 essential proteins
are involved
Actin and Myosin

3. MYOSIN
Assembled myosin filament
Light meromyosin
Heavy Meromyosin
Head –
ATPase active site,
actin binding site

4. 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

5. 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

6. SERIES OF EVENTS IN CONTRACTION
Step 1 : Depolarization of sarcolemma

7. Step 2 : Release of Ca ions
Step 3 : Conformational changes in actin

8. Step 4 : Formation of
Actomyosin complex
Step 5 : Interaction of
thick and thin
filaments
• Power stroke

9. Ratchet mechanism
Walk along mechanism

10. ROLE OF CALCIUM
Ca
Troponin
Tropomyosin
Actin
Myosin

11. 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

12. REPHOSPHORYLATION OF ATP
1.Phosphagen
Creatine phosphate
Creatine phosphate + ADP ATP + Creatine
2 .Breakdown of muscle carbohydrate

13. Lactic acid formation
Muscle fatigue
Oxygen debt
Cori cycle
4/5th
of lactic acid = glycogen
1/5th
of lactic acid = water + Carbondioxide

14. Thanku…….