muscles Flashcards
1a) What is the role of ATP in myofibril contraction?
(Reaction with ATP) breaks/allows binding of myosin to actin/ actinomyosin bridge; Provides energy to move myosin head;
1c )The mice that were not able to produce creatine were homozygous for a recessive allele of a gene. Mice that are heterozygous for this allele are able to produce forces similar to those of normal mice that are homozygous for the dominant allele of the same gene.
Explain why the heterozygous mice can produce forces similar to those of normal mice.
(Heterozygous) have one dominant/normal allele (for creatine production);
(This) leads to production of enough/normal amount of creatine;
2a )Describe the roles of calcium ions and ATP in the contraction of a myofibril.
- Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum;
-Calcium ions) cause movement of tropomyosin (on actin);
-(This movement causes) exposure of the binding sites on the actin; Myosin heads attach to binding sites on actin;
-Hydrolysis of ATP (on myosin heads) causes myosin heads to bend;
(-Bending) pulling actin molecules;
-Attachment of a new ATP molecule to each myosin head causes myosin heads to detach (from actin sites).
2(b) ATP is an energy source used in many cell processes. Give two ways in which ATP is a suitable energy source for cells to use.
.
1 .Releases relatively small amount of energy / little energy lost as heat;
- Releases energy instantaneously;
- Phosphorylates other compounds, making them more reactive;
- Can be rapidly re-synthesised;
- Is not lost from / does not leave cells.
3a)Mitochondrial disease (MD) often causes muscle weakness (lines 1–3). Use your knowledge of respiration and muscle contraction to suggest explanations for this effect of MD.
- Less force generated because fewer actin and myosin interactions in muscle;
- Fatigue caused by lactate from anaerobic respiration.
1-Reduction in ATP production by aerobic respiration;
c)Suggest how the change in the anticodon of a tRNA leads to MD
Change to tRNA leads to wrong amino acid being incorporated into protein; Tertiary structure (of protein) changed;
Protein required for oxidative phosphorylation / the Krebs cycle, so less / no
ATP made.
(d) If someone has MD, the concentration of lactate in their blood after exercise is usually much higher than normal (lines 15–17). Suggest why.
Mitochondria / aerobic respiration not producing much / any ATP;
(With MD) increased use of ATP supplied by increase in anaerobic respiration; More lactate produced and leaves muscle by (facilitated) diffusion.
5a)Both slow and fast muscle fibres contain ATPase.
Explain why.
Muscle) contraction requires energy / ATP;
Splitting / breakdown / hydrolysis of ATP;
3. Use of ATP by myosin.
5(b) The tissue in the diagram came from muscle with a high proportion of brown-staining fibres. Was the tissue removed from slow or fast skeletal muscle?
Explain your answer.
Fast because (lots of) ATPase allows rapid hydrolysis of ATP
or
Slow because (lots of) ATPase allows rapid synthesis of ATP.
5c)The muscle tissue in the diagram had been stained for viewing with a microscope.
What is the evidence that it had been stained for viewing with an optical (light) microscope? Explain your answer.
1.
Need light to see colour / brown / yellow;
- Cannot see colour / brown / yellow with electrons / an electron microscope;
- No organelles are visible.
7 In which type of athlete would the sports scientist expect to find muscle fibres with the highest number of mitochondria?
-Explain the reason for your choice of athlete.
(Group) 5 / marathon runners.
5 / marathon runners) have highest percentage of slow fibres;
- (Slow fibres) use aerobic respiration / aerobic respiration occurs in mitochondria;
- (Slow fibres) best for endurance / long periods of exercise / to avoid fatigue.
7b The leg muscles of long-distance cyclists are usually larger than the leg muscles of non-athletes.
Suggest why.
No (overall) change in number of fibres;
Increase in diameter of fibres;
(Due to) training / exercise;
(Long-distance) cyclists have more / higher percentage of slow fibres (than fast)
low fibres of wider diameter than fast fibres; (Long-distance) cyclists have more mitochondria; (Long-distance) cyclists have more capillaries (in muscles).
7c A reader of the sports scientist’s results stated that ‘the results show that regular weightlifting changes your proportion of slow and fast skeletal muscle fibres.’
Weightlifting favoured by / weightlifters have a high proportion of fast / low proportion of slow fibres
8(a) What is the role of phosphocreatine (PC) in providing energy during muscle contraction
(Phosphocreatine) provides phosphate / phosphorylates;
To make ATP;
8b ) There is a lot of variation in the time taken for PC to be re-formed in people of a very similar age.
Suggest one reason for this variation.
Genetic differences;
Level of fitness / amount of regular exercise done / mass of muscle;
Sex;
Ethnicity
Metabolic rate;
Number of fast / slow muscle fibres
9 (a) Describe the part played by each of the following in myofibril contraction.
(i) Tropomyosin
myosin
Moves out of the way when calcium ions bind;
Allowing myosin to bind (to actin) / crossbridge formation;
9b he high glycogen content of fast muscle fibres
the number of capillaries supplying slow muscle fibres.
(Glycogen broken down) gives (lots of) glucose for glycolysis / anaerobic respiration;
Glycolysis / anaerobic respiration not very efficient / only yields 2 ATP per glucose;
10c
(c) 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.
- Attachment / cross bridges between actin and myosin;
Accept the role of ADP in attachment - ‘Power stroke’ / movement of myosin heads / pulling of actin;
Not just ‘filaments slide’ as given in the question stem - Detachment of myosin heads;
- Myosin heads move back / to original position / ‘recovery stroke’
11bi You could use an optical microscope and a slide of stained muscle tissue to find the diameter of one of the muscle fibres. Explain how.
Measure with graticule / eyepiece scale;
Calibrate against something of known size:
bii A student found the mean diameter for the slow muscle fibres in a section. Give two precautions that she should have taken when sampling the fibres. Give a reason for each precaution.
Equivalent measurements taken;
At random to avoid bias / avoid choice of particular fibres;
Large number to be representative / minimise effect of extremes / of anomalies;
(12d) People with mitochondrial disease have mitochondria that do not function properly.
Some people with mitochondrial disease can only exercise for a short time. Explain why a person with mitochondrial disease can only exercise for a short time.
(Mitochondria) use aerobic respiration;
Mitochondria produce ATP / release energy required for muscles (to contract);
Explain what caused the decrease in length in I band and h zone
filaments in I / thin filaments / actin filaments slide in between myosin / thick filament; thin filaments enter H zone / meet in middle of A band / pull Z lines closer
14a Labelled antibodies and an electron microscope can be used to produce images locating proteins on the surface of organelles, but cannot be used to observe cross muscle cells. Explain why.
- e.m. gives high resolution due to short wavelength of electrons;
- antibodies attach specifically to target proteins;
- gold particles are electron dense;
- electrons must pass through a vacuum so material must be dead / fixed for e.m.; 5. cross-bridge cycling requires living cells / metabolism / named aspect-e.g. ATP synthesis;
16 ii Explain the role of calcium ions and ATP in bringing about contraction of a muscle fibre.
Calcium ions
atp
Bind to troponin;
Remove blocking action of tropomyosin / expose myosin binding sites
ATP:
Allows myosin to detach from actin / to break cross bridge;
[allow attach and detach]
Releases energy to recock / swivel / activate myosin head / drive power stroke;
