The molecular Basis of contraction Flashcards
When do sarcomeres contract
When myosin interacts with actin to form a cross-bridge
What is the first step of sarcomeres contracting
An action potential travels into the muscle fibre via T tubules, which are in contact with the sarcoplasmic reticulum (muscle ER)
What is the second step of sarcomeres contracting
When the action potential reaches the sarcoplasmic reticulum, Ca2+ ion channels open and Ca2+ diffuses into the sarcoplasm
What is the third step of sarcomeres contracting
The calcium ions released by the sarcoplasmic reticulum now bind to troponin
What is the fourth step of sarcomeres contracting
The calcium ion binding to the troponin causes the tropomyosin molecule to move, which exposes the myosin binding site on the actin filament
What is the fifth step of sarcomeres contracting
The exposing of the myosin binding site allows myosin to attach to actin and form the actin-myosin cross-bridge
What is the sixth step of sarcomeres contracting
Once the myosin is attached to actin, the myosin heads change shape, pulling the actin filament along which releases a molecule of ADP
What is the seventh step of sarcomeres contracting
A molecule of ATP attaches to the myosin head, causing it to change shape and detach from the actin filament
What is the eighth step of sarcomeres contracting
ATPases are activated by the Ca2+ ions released by the sarcoplasmic reticulum
What is the ninth step of sarcomeres contracting
The ATPases break down the ATP attached to the myosin heads which allows the myosin heads to return to its original position
What is the tenth step of sarcomeres contracting
The myosin heads are now detached and can attach to another binding site further down the actin filament and the process repeats
What does this process result in
The actin filaments in one sarcomere being pulled in opposite directions, towards each other
What happens as the filaments slide past each other
It causes the sarcomere to shorten, this is called sliding filament theory
