Topic 7B (Muscles, skeleton, heart and breathing)

The diagram below shows a sarcomere of a muscle.
Label the following.

P = I band (where only thin actin present)

Q = Z- line

R = H band (where only thick myosin is present)

S = M line

Describe the role of calcium ions in the sliding filament theory of muscle contraction

(4 marks)

- calcium ions bind to troponin (ball thing)

- changing the shape of troponin

- this causes tropomyosin to move away from the myosin binding site

(tropomyosin is kinda like a thin string attached to troponin)

- myosin head then binds onto actin, forming an actin-myosin cross bridge

Describe the role of ATP in muscle contraction
(4 marks)

- ATP binds to the myosin head

- breaking the actin-myosin cross-bridge
(OR releasing the myosin head from the actin strand )

- ATP is hydrolysed by the myosin head
(ATP broken down into ADP)

- providing energy to move the myosin head back/upright

Compare and contrast the structure of fast-twitch and slow-twitch muscle fibres.

(5 marks)

- both contain actin & myosin

- both consist of sarcomeres

- slow twitch have more mitochondria than fast-twitch
(allows more respiration)

- slow-twitch has more myoglobin & capillaries than fast-twitch
(allows for greater store of O2)

- fast twitch are larger in diameter & longer than slow twitch

(slow-twitch muscle fibres contracts slowly and fast contracts rapidly)

- calcium ions bind to troponin, changing it’s shape
- this causes tropomyosin to move and allows myosin to bind to actin