Sliding Filament Model/Power Stroke

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1. Outline the structure of myosin

  • The myosin filament is formed from a number of myosin proteins wound together, each ends in a myosin head, which contains an ATPase
  • ADP and Pi, this entire process repeats, causing the sarcomere to contract fully
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2. The A band in the structure of the sarcomere is

  • Found at the centre of the myosin filaments, no myosin heads are in this region of myosin filaments
  • 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)

3. There is only sufficient ATP available in a muscle fibre for around

  • 1-2 seconds worth of contraction
  • 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

4. The H zone in the structure of the sarcomere is

  • The zone which lies within an A band, it only contains myosin filaments
  • Found at the centre of the myosin filaments, no myosin heads are in this region of myosin filaments
  • Defines the limits of the sarcomere, they appear as thin dark lines under a microscope
  • The region that only contains actin filaments (it is lightest coloured bands of the sarcomere, when viewed under a microscope)

5. In the second stage of 'The power stroke', upon binding to the actin, the myosin heads change shape, pulling the thin actin filaments towards the centre of the sarcomere, so they

  • Attaching themselves to the binding sites on actin
  • Overlap more with the thick filament. This stage is specifically known as the power stroke
  • ADP and Pi, this entire process repeats, causing the sarcomere to contract fully

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