Muscles

Question 1

People who have McArdle’s disease produce less ATP than healthy people. As a result, they are not able to maintain strong muscle contraction during
exercise.

Use your knowledge of the sliding filament theory to suggest why.
(4)

Answer 1

1. Energy from ATP is needed for… (EXAMPLE - Active transport of Ca2+ back to Sarcoplasmic reticulum);
2. Attachment/cross bridges between actin and myosin;
3. ‘Power stroke’ / movement of myosin heads / pulling of actin;
4. Detachment of myosin heads;
5. Myosin heads move back/to original position / ‘recovery stroke”;

Question 2

Describe the part played by tropomyosin in myofibril contraction
&
Describe the part played by myosin in myofibril contraction.

Answer 2

Tropomyosin:
1. Exposes myosin binding sites when calcium ions bind;
2. Allowing myosin to bind to actin / cross bridge formation;

Myosin:
1. Head (of myosin) binds to actin and moves/pulls/slides actin past;
2. (Myosin) detaches from actin and re-sets / moves further along (actin)
3. Using energy from ATP;

Question 3

The mitochondria in muscles contain many cristae.
Explain the advantage of this (2)

Answer 3

1. Larger surface area for oxidative phosphorylation / electron carrier system;
2. provide ATP & energy for (muscle) contraction;

Question 4

! Explain why increased cardiac output is an advantage during exercise (5)

Answer 4

1. In exercise more energy released / more respiration / actively respiring muscles / for aerobic respiration;
2. Higher cardiac output - Increases O2 supply (to muscles);
3. Increases glucose supply (to muscles);
4. Increases COz removal (from muscles) / lactate removal;
5. Increases heat removal (from muscles) / for cooling.

Question 5

Explain the importance of ATP hydrolase during muscle contraction (2)

Answer 5

1. Hydrolyses ATP yielding energy;
2. used to form / break actomyosin bridges;

Question 6

Muscle contraction requires ATP.
What are the advantages of using aerobic rather than anaerobic respiration to provide ATP in a long-distance race?

Answer 6

1. Aerobic respiration produces more ATP / releases more energy;
2. Little/no lactate produced / does not accumulate;
3. Avoids cramp / muscle fatigue;
4. CO2 easily removed from the body / CO2 removed by
   breathing;

Question 7

A muscle fibre contracts when it is stimulated by a motor neuron.
Describe how transmission occurs across the synapse between a motor neuron and a muscle fiber.

Answer 7

1. Ca2+ channel proteins open;
2. Ca2+ ions enter (neuron) by facilitates diffusion;
3. Vesicles FUSE with presynaptic membrane;
4. Release / exocytosis of transmitter / of acetylcholine;
5. Diffusion (of transmitter) across synaptic cleft;
6. (Transmitter) binds to receptors in postsynaptic membrane;
7. Na+ channels open / Na+ ions enter (postsynaptic side);

Question 8

After death, cross bridges between actin and myosin remain firmly bound resulting in rigor mortis. Explain what causes the cross bridges to remain firmly bound (3)

Answer 8

1. Respiration stops;
2. No ATP produced;
3. ATP required for separation of actin and myosin/cross bridges;

Question 9

Describe the role of calcium ions in the contraction of a sarcomere (4)

Answer 9

1. Interact with tropomyosin;
2. To reveal binding sites on actin; (not active sites)
3. allowing myosin (heads) to bind forming a crossbridge / actinomyosin formed;
4. activates ATP hydrolase so energy is released from ATP;

Question 10

Describe fast twitch muscle fibres:

Answer 10

1. Used for rapid / strong / powerful contractions;
2. Phosphocreatine used up rapidly during contraction/to make ATP;
3. Anaerobic respiration involved;
4. ATP used to reform phosphocreatine;
5. Lots of phosphocreatine in fast twitch fibers.

Question 11

Describe the role of phosphocreatine (2)

Answer 11

1. Stores of phosphate ions / provides phosphate / phosphorylates;
2. To synthesise ATP;

(Energy from ATP allows muscles to contract)