Describe the roles of ATP in muscle contraction.
- To break actinomyosin (bridges);
- To move/bend the myosin head/arm;
- (So) actin (filaments) are moved (inwards);
- For active transport of calcium ions (into the sarcoplasmic/endoplasmic reticulum);
Explain how a decrease in the concentration of calcium ions within muscle tissues could cause a decrease in the force of muscle contraction.
- (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.
- (Fewer/No) actinomyosin bridges formed; Accept actin and myosin do not bind. Reject active site only once.
- 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.
what happens during sliding filament theory?
1.muscle cell CSM depolarised, Ca2+ channels open
2. Ca2+ diffuse from sarcoplasmic reticulum to sarcoplasm then to myofibril
3.Ca2+ bind to calcium binding sites
4. tropomyosin moves, exposes myosin binding sites on actin
5. form actinomyosin bridges by myosin head binding to myosin binding sites on actin
6. myosin heads bend, release APD + Pi, pulls actin filaments to centre of sarcomere in rowing motion
7. ATP breaks actinomyosin bridge, myosin detach from actin filament
8. ATP hydrolysed into ADP + Pi by ATPase activated by Ca2, myosin moved back to original position
(9. head attaches to another binding site, process repeated)
