The sliding muscle filament model Flashcards
What happens during contraction?
The myosin filaments pull the actin filaments inwards towards the centre of the sarcomere
Light band becomes narrower
Z-lines move closer together, shortening the sarcomere
The h-band becomes narrower
The dark bands remain the same width as the myosin filaments themselves have not shortened
What is the structure of myosin?
Myosin filaments have globular heads that are hinged which allows them to move back and forwards
Myosin head on a myosin tail
On the head is a binding site for each of the actin and ATP
What is the structure of actin?
Actin-myosin binding sites
The binding sites are often blocked by the protein tropomyosin - therefore the myosin heads can not bind to the actin
What happens to actin when a muscle is contracted?
Simplified 4 points
The myosin heads form bonds with actin filaments known as actin-myosin cross-bridges
The myosin heads then flex, pulling the actin filament along the myosin filament
The myosin filament then detaches from the actin and its head returns to the original angle, using ATP
The myosin then reattaches further along the actin filament and this process repeats
Outline the sliding muscle filament
7 stages
1) Tropomyosin prevents myosin head fro attaching to the binding site on the actin molecule.
2) Calcium ions released from the endoplasmic reticulum cause the tropomyosin molecule to pull away from the binding sites on the actin molecule
3) Myosin head now attaches to the binding site on the actin filament
4) Head of myosin changes angle, moving the actin filament along as it does so.
- The ADP molecule is released
5) ATP molecule fixes to myosin head, causing it to detach from the actin filament
6) Hydrolysis of ATP to ADP by myosin provides the energy for the myosin head to resume it’s normal position
7) Head of the myosin reattaches to a binding site further along the actin filament and the cycle is repeated
