exam questions

Question 1

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

Answer 1

• calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum
• (calcium ions) cause movement of tropomyosin (on actin)
• (this movement causes) exposure of the binding sites on the actin
• myosin heads attach to the binding sites on actin
• hydrolysis of ATP (on myosin heads) causes myosin heads to bend
• (bending) pulling actin molecules
• attachment of a new ATP molecule to each myosin head causes myosin heads to detach (from actin sites)