Calcium ions trigger tropomyosin movement to expose actin binding sites, allowing myosin heads (energized by ATP hydrolysis) to bind and pull actin, causing contraction. ATP detachment from myosin heads resets the cycle.
Beschrijf de rollen van calciumionen en ATP bij de contractie van een myofibril (5 punten)
| Front | Describe the roles of calcium ions and ATP in the contraction of a myofibril ( 5 marks) |
|---|---|
| Back | 1. Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum; 2. (Calcium ions) cause movement of tropomyosin (on actin); 3. (This movement causes) exposure of the binding sites on the actin; 4. Myosin heads attach to binding sites on actin; 5. Hydrolysis of ATP (on myosin heads) causes myosin heads to bend; 6. (Bending) pulling actin molecules; 7. Attachment of a new ATP molecule to each myosin head causes myosin heads to detach (from actin sites); |
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