Module 6- Skeletal muscles Flashcards
5 marks
Describe the roles of calcium ions and ATP in the contraction of a myofibril
- Calcium ions diffuse into myofibrils from sarcoplasmic reticulum
- Movement of tropomyosin (calcium ions distort ionic bonds of protein)
- Actin-myosin binding sites exposed
- Actin-myosin crossbridge forms
- Hydrolysis of ATP (on myosin heads) causes myosin heads to bend
- Myosin head bends and does a powerstoke
- Attachment of a new ATP molecule to each myosin head causes myosin heads to detach from actin sites
2 marks
Describe the part played by tropomyosin in myofibril contraction.
- Moves out of the way when calcium ions binds (disorts ionic bonds of protein)
- Allowing actin-myosin crossbridge form
2 marks
Describe the part played by myosin in myofibril contraction.
- Head of myosin binds to actin- actin myofilament pulled and slides over the myofilament (‘powerstroke’)
- Myosin detaches from actin and re-sets (‘recovery position’)
- This uses ATP
2 marks
Role of phosphocreatine in providing energy during muscle contraction
- Provides phosphate
- To make ATP
3 marks
Why do long- distance cyclists usually have larger leg muscles than non-athletes
- No overall change in number of fibres
- Increase in diameter of fibres
- Due to training/exercise
- Have higher % of slow fibres than fast
- Have more mitochondria, more capillaries
When the muscle fibre contracts, which zones/ bands decrease in length or remain unchanged in length
Remain unchanged in length
* A-band
Decrease in length
* H-zone
* I-band
2 marks
What caused the decrease in length of the H-zone and I-band
- Actin myofilament pulled and slides over the mysoin myofilament
- Pulls Z-lines closer
Use your knowledge of how myosin and actin interact to suggest how the myosin molecule moves the mitochondrion towards the presynaptic membrane.
- Myosin head attaches to actin and bends - performs powerstroke;
- This pulls mitochondria past / along the actin;
- Next myosin head attaches to actin and bends - performs powerstroke
2 marks
Why do both fast and slow muscle fibres contain ATPase
Hydrolysis of ATP
Muscle contraction requires ATP
Use of ATP for myosin
Explain the difference between fast and slow twitch muscles
Fast twitch
* Intense exercise- weightlifting
* Contract rapidly
* More powerful contraction
* Adapted for anaerobic respiration
* Phosphocreatine stores
Slow twitch
* Endurance- marathon
* Contract slowly–> less powerful contraction
* Adapted for aerobic respiration
* Lots of mitochondria
* Lots of blood vessels
* Myoglobin –> increase O2 stores
4 marks
Explain what leads to the differences in appearance between the relaxed myofibril and the contracted myofibril.
When contracted:
Myosin & actin overlap more
Interaction between myosin heads & actin / cross-links form
Movement of myosin head
Actin myofilament is pulled and slides over myosin myofilament
Movement of actin pulls Z-lines closer together
Movement of tropomyosin to allow interaction
Role of Ca2+
Role of ATP
2 marks
In muscles, pyruvate is converted to lactate during prolonged exercise.
Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration.
- Reduced NAD is oxidised to NAD
- So glycolysis can continue
3 marks
The scientists then compared the length of time that the control mice and the trained mice could carry out prolonged exercise. The trained mice were able to exercise for a longer time period than control mice.
Explain why.
- Increase aerobic respiration–> more ATP is produced
- Delay in anaerobic respiration
- Less lactate
3 marks
Damage to the myelin sheath of neurones can cause muscular paralysis. Explain how.
- Depolarisation happens along whole length of axon rather than saltatory conduction
- And so impulses are slower to reach the NMJ
- Muscles do not recieve the impulses to contract
2 marks
Suggest and explain why a drug was injected per unit of body mass
- Individuals have different masses
- Allows for comparison
