6.3 - Skeletal muscles Flashcards
Explain the banding pattern shown in a single sarcomere. (3)
- Light/I band only actin
- H zone/band only myosin
- Darkest/overlapping region actin and myosin
Explain how a decrease in the concentration of calcium ions within muscle tissues could cause a decrease in the force of muscle contraction. (3)
- (Less/No) tropomyosin moved from binding site
/ Shape of tropomyosin not changed so binding site not exposed/available - (Fewer/No) actin-myosin bridges formed
‘accept actin and myosin do not bind’ - Myosin head does not move / does not pull actin (filaments)
/ (Less/No) ATP (hydrol)ase (activation)
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. (2)
- 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
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. (3)
- Low pH changes shape of calcium ion receptors
- Fewer calcium ions bind to tropomyosin
- Fewer tropomyosin molecules move away
- Fewer binding sites on actin revealed
- Fewer cross-bridges can form / fewer myosin heads can bind
Describe the roles of calcium ions and ATP in the contraction of a myofibril. (5)
- 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)
What is the role of ATP in myofibril contraction? (2)
- (Reaction with ATP) breaks/allows binding of myosin to actin/ actin-myosin bridge
- Provides energy to move myosin head
Define the term antagonistic muscle action. (2)
- Muscles work in pairs
- One muscle pulls in one direction (at a joint) and the other muscle pulls in the opposite direction
Explain the presence of a large number of mitochondria in the sarcoplasm of a muscle fibre. (2)
- Mitochondria provide ATP from aerobic respiration
- This ATP binds to myosin causing it to detach from the actin / to break cross bridge
- ATP is hydrolysed to release energy to change the shape of / recock the myosin head
- Active transport of calcium ions/Ca2+ requires ATP
Describe the effect of muscle fibre contraction on the length of the A-band and the sarcomere. (2)
- The A-band will remain the same length
- The sarcomere will shorten / decrease in length
Identify the role of phosphocreatine in providing energy during muscle contraction. (2)
- Phosphocreatine is a source of phosphate / phosphorylates
- For the synthesis/formation of ATP
- ADP + phosphocreatine → ATP + creatine
State the role of calcium ions during muscle contraction. (2)
- Calcium ions / Ca2+ binds to troponin/ causes troponin to change shape
- (As a result) tropomyosin moves away exposing the binding sites on the actin molecules
- The myosin heads can now bind to the actin filaments / form cross-bridges (to allow muscle contraction)
State the reason for high levels of glycogen in fast muscle fibres. (2)
- (Glycogen) is broken down to provide glucose
- (This glucose is required for) glycolysis / anaerobic respiration
- Anaerobic respiration is inefficient / only provides a small amount of ATP, so large quantities of glycogen are required
/ large quantities of glycogen are required to ensure a sufficient quantity of ATP is generated (from glycolysis)
Fast muscle fibres have fewer capillaries than slow muscle fibres. Explain why. (2)
- Fast muscle fibres rely on anaerobic respiration for ATP / slow muscle fibres rely on aerobic respiration so require a denser network of capillaries
- (Because respiration is anaerobic and not aerobic) there is less of a requirement for a blood supply due to a lower oxygen requirement
Suggest why slow muscle fibres contain a large amount of myoglobin. (2)
- Myoglobin stores oxygen in the muscles
- This means that there is more oxygen available for aerobic respiration
- Slow muscle fibres obtain ATP from aerobic respiration
Give four differences between slow and fast muscle fibres. (4)
- Slow muscle fibres have a longer contraction-relaxation cycle
- Slow muscle fibres have a smaller store of calcium ions in the sarcoplasmic reticulum
- Slow muscle fibres obtain ATP mostly from aerobic respiration / fast muscle fibres obtain ATP mostly from anaerobic respiration
- There is a greater number of larger mitochondria near the surface of slow muscle fibres
- There is a slower rate of ATP hydrolysis in myosin heads in slow muscle fibres
- Slow muscle fibres are more resistant to fatigue as less lactate is formed
