muscle contraction

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.

Answer 1

Detachment of myosin heads;
Myosin heads move back / to original position and ATP hydrolysed into ADP and Pi

ADP and Pi used so myosin head can bind to actin filament bonding site which forms cross bridges between actin and myosin;

less cross bridge less ‘Power stroke’ /

Question 2

Use your knowledge of fast muscle fibres to explain why for older people it takes longer for phosphocreatine to be reformed .

Answer 2

fast muscle fibres contract more quickly/ rapidly so phosphocreatine used up to form ATP

older people have a lower rate of metabolism so less aerobic respiration which provides ATP so less ATP

ATP is needed to reform phosphocreatine

Question 3

what Attaches to Z line at the end of
the sarcomere

Answer 3

Actin filament

Question 4

If myosin molecules are unable to bind to other myosin molecules, this prevents
muscle contraction.
Use the diagram and your knowledge of how muscles contract to suggest why.

Answer 4

Can’t form myosin / thick filaments;
cant slide actin past / (myosin)
can’t shorten sarcomere

Question 5

why would a marathon runner have lots of mitochondria

Answer 5

lots of slow muscle fibres
for aerobic respiration to form ATP
for endurance exercise

Question 6

The leg muscles of long-distance cyclists are usually larger than the leg muscles of
non-athletes.
Suggest why.

Answer 6

more slow muscle fibres
lots of mitochondria for ATP
lots of capillaries to supply oxygen and glucose

Question 7

ATP in muscle contraction

Answer 7

ATP is first hydrolysed into ADP and Pi, which provides energy to cock the myosin head into a high-energy position.
The myosin head (still bound to ADP and Pi) then binds to the actin filament, forming a cross-bridge.
ADP and Pi are released, triggering the power stroke — the myosin head pulls the actin filament.
A new ATP molecule then binds to the myosin head, causing it to detach from the actin.
This cycle repeats as long as calcium ions and ATP are present

Question 8

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.

Answer 8

• more aerobic respiration
  anerobic respiration is delayed
  more lactate acid produced

Question 9

During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in
pH leads to a reduction in the ability of calcium ions to stimulate muscle
contraction.
Suggest how.

Answer 9

Low pH changes shape of calcium ion receptors
2. Fewer calcium ions bind to tropomyosin;

3. Fewer tropomyosin molecules move away;
4. Fewer binding sites on actin revealed;
5. Fewer cross-bridges can form