The Sliding Filament Mechanism
Two ATP Steps — Critical NEET Distinction
| ATP Step | What Happens |
|---|---|
| ATP HYDROLYSIS (ADP + Pi) | Re-energizes (re-cocks) myosin head; energizes it for next power stroke |
| ATP BINDING (new ATP) | Causes myosin head to DETACH from actin; allows cycle to reset |
Without ATP: Myosin cannot detach → permanent cross-bridge = RIGOR MORTIS.
Key Structural Requirements
- T-tubules: Carry action potential deep into muscle fiber → rapid, uniform contraction
- Sarcoplasmic reticulum (SR): Stores and releases Ca2+; SERCA pump re-sequesters Ca2+ for relaxation
- Troponin-C: Ca2+ receptor; conformational change is the "on" switch
- Tropomyosin: The "off" switch; blocks myosin binding sites; shifted by troponin during contraction