Muscle Structure And Contraction

Question 1

Describe the roles of ATP in muscle contraction (4)

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 (3)

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);

Question 3

Describe the role of calcium ions in the contraction of a sacromere (4)

Answer 3

1. calcium binds to tropomyosin causing it to change shape
2. reaveals binding sites on actin
3. allows myosin head to bind
4. activates ATPase