Sliding Filament Model/Power Stroke

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1. The pattern of banding on myofibrils is caused by the sarcomeres, these are the smallest

  • Contractile units of the muscle and are arranged end to end for the entire length of the myofibril
  • Groups of muscle fibres surrounded by connective tissue containing blood vessels and nerves
  • A large number of myofibrils within the sarcoplasm they, like fibres, exhibit a striated pattern under the microscope
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2. When nervous stimulation stops at the neuromuscular junction, calcium ions are ________ back into sarcoplasmic reticulum by caarrier proteins on the membrane, this leads to muscle relaxtion

  • Actively transported
  • 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
  • Wound around the actin, reinforcing it

3. 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

4. A cross bridge is

  • The name given to the attatchment formed by a myosin head binding to a binding site on an actin filament
  • Wound around the actin, reinforcing it

5. Outline the structure of actin

  • The actin filament is formed from a helix of actin sub-units, each contains a binding site for the myosin heads, two other proteins, tropomyosin and troponin are attached to the actin fibre
  • ADP and Pi, this entire process repeats, causing the sarcomere to contract fully
  • Found at the centre of the myosin filaments, no myosin heads are in this region of myosin filaments


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