Question

Describe the roles of calcium ions and ATP in the contraction of a myofibril ( 5 marks)

Accepted Answer

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);

Myosin Atp Heads Calcium Ions Movement Binding Sites