Sliding Filament Model/Power Stroke

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1. In the third stage of 'The power stroke', the myosin heads use the energy in ATP to detach from the actin, the head group moves backwards as ATP is hydrolysed to

  • ADP and Pi, this entire process repeats, causing the sarcomere to contract fully
  • Attaching themselves to the binding sites on actin
  • Overlap more with the thick filament. This stage is specifically known as the power stroke
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2. When a muscle cell us undergoing anaerobic respiration, the lactate produced

  • Enters the blood, where it leads to the stimulation of increased blood supply to the muscles
  • The phosphate group from creatine phosphate can be transfered to ADP to form ATP quickly by the enzyme creatine phosphotransferase - this enables muscle contraction for a further 2 - 4 seconds

3. Myofibrils are organelles, muscle fibre is

  • A cell
  • A bird
  • A fly
  • A plain

4. Troponin molecules are

  • bound to tropomyosin, each complex consists of three polypeptides, one binds to actin, one to tropomyosin (wound around actin) and one to calcium ions
  • Wound around the actin, reinforcing it
  • Changes the shape of the troponin, which moves the tropomyosin away from the binding sites on the actin - this means cross bridges can form allowing the power stroke and muscle contraction to occur

5. The A band in the structure of the sarcomere is

  • The same length as the myosin filaments, and contains H zone and M line. Actin and myosin interlock within this band
  • The region that only contains actin filaments (it is lightest coloured bands of the sarcomere, when viewed under a microscope)
  • Found at the centre of the myosin filaments, no myosin heads are in this region of myosin filaments


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