Sliding Filament Model/Power Stroke

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1. 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)
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2. Myofibrils contained two different types of filaments: thin filaments made predominantly of actin, and

  • Found at the centre of the myosin filaments, no myosin heads are in this region of myosin filaments
  • Thick filaments made of myosin
  • Together shortening the sarcomere which is the basis of muscle contraction

3. 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

  • 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
  • Attaching themselves to the binding sites on actin

4. In the first stage of 'The power stroke', myosin head groups on the myosin filaments form cross brigdes with the surrounding filaments by

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

5. 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

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