Module 6- Skeletal muscles Flashcards

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1
Q

5 marks

Describe the roles of calcium ions and ATP in the contraction of a myofibril

A
  1. Calcium ions diffuse into myofibrils from sarcoplasmic reticulum
  2. Movement of tropomyosin (calcium ions distort ionic bonds of protein)
  3. Actin-myosin binding sites exposed
  4. Actin-myosin crossbridge forms
  5. Hydrolysis of ATP (on myosin heads) causes myosin heads to bend;
  6. Myosin head bends and does a powerstoke
  7. Attachment of a new ATP molecule to each myosin head causes myosin heads
    to detach from actin sites
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2
Q

2 marks

Describe the part played by tropomyosin in myofibril contraction.

A
  1. Moves out of the way when calcium ions binds (disorts ionic bonds of protein)
  2. Allowing actin-myosin crossbridge form
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3
Q

2 marks

Describe the part played by myosin in myofibril contraction.

A
  1. Head of myosin binds to actin- actin myofilament pulled and slides over the myofilament (‘powerstroke’)
  2. Myosin detaches from actin and re-sets (‘recovery position’)
  3. This uses ATP
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4
Q

2 marks

Role of phosphocreatine in providing energy during muscle contraction

A
  1. Provides phosphate
  2. To make ATP
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5
Q

3 marks

Why do long- distance cyclists usually have larger leg muscles than non-athletes

A
  1. No overall change in number of fibres
  2. Increase in diameter of fibres
  3. Due to training/exercise
  4. Have higher % of slow fibres than fast
  5. Have more mitochondria, more capillaries
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6
Q

When the muscle fibre contracts, which zones/ bands decrease in length or remain unchanged in length

A

Remain unchanged in length
* A-band
Decrease in length
* H-zone
* I-band

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7
Q

2 marks

What caused the decrease in length of the H-zone and I-band

A
  • Actin myofilament pulled and slides over the mysoin myofilament
  • Pulls Z-lines closer
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8
Q

Use your knowledge of how myosin and actin interact to suggest how the myosin molecule moves the mitochondrion towards the presynaptic membrane.

A
  1. Myosin head attaches to actin and bends - performs powerstroke;
  2. This pulls mitochondria past / along the actin;
  3. Next myosin head attaches to actin and bends - performs powerstroke
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9
Q

2 marks

Why do both fast and slow muscle fibres contain ATPase

A

Hydrolysis of ATP
Muscle contraction requires ATP
Use of ATP for myosin

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10
Q

Explain the difference between fast and slow twitch muscles

A

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

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11
Q

4 marks

Explain what leads to the differences in appearance between the relaxed myofibril and the contracted myofibril.

A

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

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12
Q

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.

A
  1. Reduced NAD is oxidised to NAD
  2. So glycolysis can continue
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13
Q

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.

A
  1. Increase aerobic respiration–> more ATP is produced
  2. Delay in anaerobic respiration
  3. Less lactate
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