Muscle contraction Flashcards
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
What is the equation for the production of ATP using the ATP-phosphocreatine system?
ADP + PCr -> ATP + Cr (creatine)
Where is PCr stored?
In cells
When is PCr used?
Short bursts of vigorous exercise
What are the features of the ATP-PCr system?
Anaerobic
Alactic
What does some of the creatine get broken down into?
Creatinine
How is creatinine removed from the body?
Via the kidneys
In what type of people are creatinine levels high in?
People who exercise regularly and those with a high muscle mass
What does high creatinine levels indicate?
Kidney damage
How does the ATP-PCr system generate ATP?
ADP becomes phosphorylated into ATP and the phosphate comes from the PCr
Do slow twitch muscle fibres contract slowly or quickly?
Slowly
How long can slow twitch muscle fibres work for?
Long periods of time without getting tired
What are slow twitch muscle fibres good for?
Endurance activities
Where are high proportions of slow twitch muscle fibres found?
In the muscles for posture eg. back and calves
What type of respiration is used in slow twitch muscle fibres?
Slowly through aerobic respiration
What do slow twitch muscle fibres have?
Lots of mitochondria and blood vessels to supply the muscle with oxygen
Where are the mitochondria in slow twitch muscle fibres found and why?
The edge of muscle fibres
Short diffusion pathway for oxygen from the blood vessels to the mitochondria
What is myoglobin?
Red-coloured protein that stores oxygen
Do slow twitch fibres or fast twitch fibres have lots of myoglobin?
Slow twitch muscle fibres
Do fast twitch muscle fibres contract fast or slow?
Very fast
How long can fast twitch muscle fibres contract for?
Short periods of time as they get tired really quickly
What are fast twitch muscle fibres good for?
Short bursts of speed and power
Where are high amounts of fast twitch muscle fibres found?
In muscles that you use for fast movement, such as legs, arms and eyes
How is energy released in fast twitch muscle fibres?
Quickly through anaerobic respiration
What do fast twitch muscle fibres have stores of? Why?
PCr
So energy can be generated very quickly when needed
What do fast twitch muscle fibres not have a lot of?
Mitochondria
Blood vessels
Myoglobin
