Muscle contraction Flashcards
(49 cards)
What is the structure of a myosin filament?
They have globular heads that are hinged, they can move back and forth. Each myosin head has a binding site for actin and a binding site for ATP
What is the structure of an actin filament?
They have binding sites for myosin heads (actin-myosin binding sites).
What protein is found between actin filaments?
Tropomyosin
What is the purpose of tropomyosin?
Helps myofilaments move past each other
What is the myosin-actin binding site like in a resting muscle?
Blocked by tropomyosin which means that the myofibrils cant slide past each other because the myosin heads cant bind to the actin filaments
What happens to the sarcolemma when an action potential arrives?
It becomes depolarised
What happens once the sarcolemma has become depolarised?
Depolarisation spreads down the T-Tubules in the sarcoplasmic reticulum
When the T-Tubules become depolarised, what happens?
The sarcoplasmic reticulum releases stored calcium ions into the sarcoplasm and this influx causes muscle contraction
What role do Ca2+ ions have in muscle contraction?
They attach to tropomyosin which causes the protein to change shape, pulling it out of the actin-myosin binding site on the actin filament
What is the actin-myosin cross bridge?
The bond formed when a myosin head binds to an actin filament
What do Ca2+ ions activate?
ATP hydrolase
What does ATP hydrolase do?
Hydrolyses ATP into ADP and Pi to provide the energy needed for the muscle contraction
What does the energy released from the ATP being hydrolysed also do?
Causes the myosin head to bend which pulls the actin filament along in a kind of rowing action
How is the actin-myosin cross bridge broken?
Another ATP molecule provides the energy to break the actin-myosin cross bridge so the myosin head detaches from the actin filament after its moved
What does the myosin head do once the actin-myosin cross bridge is broken?
Returns to its starting position and reattaches to a different binding site further along the actin filament
What rate do actin-myosin cross bridges form and break?
Very rapidly
What happens when the muscle stops being stimulated?
Calcium ions leave their binding sites and are moved by active transport back into the sarcoplasmic reticulum.
This causes the tropomyosin molecules to move back so they block the actin-myosin binding sites again
What happens to the sarcomere and actin filaments when the muscles aren’t contracted?
The sarcomere lengthens as the actin filaments slide back to their relaxed position
What three ways is the ATP generated for muscle contraction?
1) Aerobic respiration
2) Anaerobic respiration
3) ATP-Phosphocreatine system
How is ATP generated in aerobic respiration?
Mostly generated in oxidative phosphorylation in the cell’s mitochondria
When is using aerobic respiration good?
Long period of low intensity exercise
How is ATP generated in anaerobic respiration?
it is generated rapidly in glycolysis, the end product in glycolysis is pyruvate
What is the issue with anaerobic respiration?
When pyruvate is converted to lactate by lactate fermentation, lactate can build up in the muscles and cause muscle fatigue
When is using anaerobic respiration good?
Short periods of hard exercise
