3.6.6: Muscle structure and contraction Describe the roles of ATP in musc

Question 1

Describe the roles of ATP in muscle contraction.

Answer 1

1. To break actinomyosin (bridges);
2. To move/bend the myosin head/arm;
3. (So) actin (filaments) are moved (inwards);
4. For active transport of calcium ions (into the sarcoplasmic/endoplasmic reticulum);

Question 2

Explain how a decrease in the concentration of
calcium ions within muscle tissues could cause a
decrease in the force of muscle contraction.

Answer 2

1. (Less/No) tropomyosin moved from binding site
   OR
   Shape of tropomyosin not changed so binding site not exposed/available;
   Ignore troponin.
   Reject active site only once.
2. (Fewer/No) actinomyosin bridges formed;
   Accept actin and myosin do not bind.
   Reject active site only once.
3. Myosin head does not move
   OR
   Myosin does not pull actin (filaments)
   OR
   (Less/No) ATP (hydrol)ase (activation);
   Reject ATP synthase.
   Do not penalise reference to calcium rather than calcium ions.
   Credit all mark points even if context relates to what happens when calcium
   ions are present.