exam questions

• Describe the changes when calcium ions are released from the sarcoplasmic reticulum (2)

  -       troponin changes shapes so troponin moves tropomyosin

  -       myosin binding sites on actin are exposed 
• explain how these changes cause a muscle to contract (4)

  -       myosin heads can bind to the binding sites 

  -       myosin then changes shape, bending forward 

  -       actin filament is pulled over the myosin 

  -       therefore, the sarcomere shortens/muscle fibre shortens 

  -       ATP is hydrolysed and ADP + PI are released
• Describe the action between troponin and tropomyosin which allows muscles to contract (2)

  -       Troponin changes shape 

  -       Causing tropomyosin to move away/expose the myosin binding sites 
• Explain the importance of the primary structure of ATPase (3)

  -       Primary structure determines interaction between amino acids e.g., bonds forming between R groups 

  -       The primary structure determines then folding of the protein/the tertiary structure 

  -       Therefore, affecting the shape of the active site 

  -       Making active site complementary to ATP
• Describe how the concentration of calcium ions around myofibrils is controlled (3)

  -       Calcium ions are released from sarcoplasmic reticulum 

  -       In response to an action potential arriving at neuromuscular junction 

  -       Calcium channels open to allow calcium ions to enter the sarcoplasm 

  -       Calcium ions taken back up into the sarcoplasmic reticulum by active transport after muscle contraction.
• Explain how the extensor and flexor muscles bring about movement in the lower leg (2)

  -       Tendons attach muscles to bones 

  -       The flexor and extensor act as antagonistic pairs 

  -       When extensor contracts it pulls on the tibia to extend the leg, the flexor muscle contracts it pulls on the fibula flexing the leg
• Describe 2 structural differences between fast twitch muscle fibres and slow twitch (2)

  -       Fast twitches have few mitochondria and slow twitch have many mitochondria 

  -       Fast twitches have fewer capillaries whereas slow twitch have many.
• Explain how the structure of a muscle fibre is related to its specialised function (3)

  -       Sarcolemma contains voltage gated channels which allows depolarisation of muscle fibres 

  -       Many mitochondria for aerobic respiration 

  -       Presence of myofibrils/sarcolemma’s/actin and myosin.
• Describe how the tertiary structure of myosin is related to its function (3)

  -       Part of myosin molecule is folded to form a globular head 

  -       That can bind to myosin binding sites on actin 

  -       Myosin also has a binding site that can bind with ATP 

  -       Straight part of myosin molecule forms a bundle with other myosin molecules 
• Explain the effect of increasing calcium ion conc of the mean force produced by muscle fibres (4)

  -       As calcium ion conc increases so does force produced 

  -       Because more actin and myosin forming cross bridges 

  -       There is no increase in force produced at high calcium ion conc 

  -       As all actin and myosin are interacting and all myosin binding sites are occupied
• during intense exercise, the PH of the skeletal muscle tissue falls sharply, this decrease in PH reduces ability of calcium ions to stimulate muscle contraction, how?(4)

  • Low pH changes the shape of the calcium ion receptors
  • (This means that) fewer calcium ions will bind to troponin
  • (So) fewer tropomyosin molecules move (away) / change shape
  • This causes fewer binding sites on actin to be revealed
  • (So) fewer cross-bridges can form / fewer myosin heads can bind (to actin)
• compare and contrast slow and fast twitch muscle fibres(6)

  similarities:

  • both produce energy and help in movement, both generate force by contraction

  differences:

  • Slow twitch are used for endurance whereas fast twitch is for short bursts of activity
  • Appearance: fast twitch fibres are thicker whereas slow twitch fibres are thinner
  • Slow twitch have slow contractions for a long period of time whereas fast twitch have fast contractions for a short period of time
  • low twitch slow rate of ATP hydrolysis (in myosin heads) whereas fast twitch has higher rates of ATP hydrolysis (in myosin heads)
• elite sprinters tend to be bulkier and more muscular than long distance runners, explain why(2)

  • elite sprinters have a greater percentage of fast twitch muscle fibres- short bursts of high energy
  • fast twitch muscle fibres have thicker diameter than slow twitch muscles
• describe the action taken by muscles when a pair of antagonistic muscles work together, give a named example(3)

  • as one muscle contracts the other relaxes/strengthen
  • the flexor muscle bends a joint during contraction and extenfor straightens a joint during contraction
  • muscles that is contracting is the agonist, the muscle that is lengthening is the antagonist

  eg biceps(flexor), tricept(extensor)
• describe the difference between tendons and ligaments(1)

  • tendons connect muscle to bones whereas ligaments connect bones to bones
• explain the striped appearance of the skeletal muscle(3)

  • myosin filaments are thicker so areas containing myosin are darker in appearance(and myosin along with actin areas)
  • actin filaments are thinner so areas containing only actin are lighter in appearance