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Muscles and the sliding filament mechanism

Biology A2 Unit 5

Jane Hampson

on 23 February 2015

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Transcript of Muscles and the sliding filament mechanism

Structure of Skeletal Muscle.
In the light microscope, skeletal muscle fibres have a stripey appearance. These muscles are called 'striated' (or striped) muscles. This appearance is a consequence of the distribution of two different proteins: actin and myosin.
Electron micrograph appearance of striated muscle
This shows that the muscle fibres are made of repeating subunits. These are called
and each originates from one 'cell'. In muscle fibres, many cells fuse to form a syncytium, with the nuclei and mitochondria dispersed around the sarcomeres.
Sarcomere structure
Copy the diagram from the board, to show the relative positions of the thin
filaments and the thicker
So, muscle 'contraction' or shortening occurs because the actin and myosin filaments slide past each other.
An action potential in the sarcolemma causes calcium channels to open and calcium diffuses into the muscle fibre.

Calcium binds to tropomyosin on the actin filament. This changes shape and moves, exposing myosin-binding sites.

Cross-bridges form between actin and myosin: the myosin heads then flex, pulling the actin filament past the myosin filament.
Muscles and the mechanism of muscle contraction
Learning objectives:
muscle structure and ultrastructure
sliding filament mechanism

What do you think happens when the muscle contracts?
What makes the filaments slide past each other?
The role of ATP
ATP bind to myosin heads, allowing the crossbridge to break. The ATP then splits into ADP and Pi. The energy released is used to return the myosin head to its unflexed position, ready for formation of a new cross-bridge.
The role of Calcium
Calcium is needed to bind to tropomyosin, revealing the myosin-binding site on actin.
Calcium is also needed to activate the ATPase function on the myosin heads, to release the crossbridge
Full transcript