Role of calcium in striated Muscle contraction

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Last updated 6:18 AM on 4/2/26
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6 Terms

1
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Starting point

  • thin filaments made up of actin, dark spot represents the myosin binding site on the actin

  • can see other thin filament proteins which include tropomyosin which is the gold thread

  • the tropomyosin covers the myosin biding site on the thin filaments

  • proteins troponin which there are three of
    - troponin regulates the position of tropomyosin

  • in red, those are the myosin heads

  • in this position the myosin can not form a cross bridge with the thin filaments because tropomyosin covers up the myosin binding site on the actin
    - the muscle is relaxed


<ul><li><p>thin filaments made up of actin, dark spot represents the myosin binding site on the actin</p></li><li><p>can see other thin filament proteins which include tropomyosin which is the gold thread</p></li><li><p>the tropomyosin covers the myosin biding site on the thin filaments</p></li><li><p>proteins troponin which there are three of<br> - troponin regulates the position of tropomyosin</p></li><li><p>in red, those are the myosin heads</p></li><li><p>in this position the myosin can not form a cross bridge with the thin filaments because tropomyosin covers up the myosin binding site on the actin<br> - the muscle is relaxed</p></li></ul><p></p>
2
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cross section through sarcomere

  • rotate the thing filaments 90 degrees (thin filaments are coming out of the screen)

  • see the actin which is the main portion of the thin filament with the myosin binding sites in these areas

  • tropomyosin and troponin are present

  • tropomyosin is really important because that can inhibit the binding of actin and myosin


<ul><li><p>rotate the thing filaments 90 degrees (thin filaments are coming out of the screen)</p></li><li><p>see the actin which is the main portion of the thin filament with the myosin binding sites in these areas</p></li><li><p>tropomyosin and troponin are present</p></li><li><p>tropomyosin is really important because that can inhibit the binding of actin and myosin</p></li></ul><p></p>
3
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Troponin complex

Proteins that make this up:
- troponin T
- troponin C ** this is the one that would regulate
- troponin I

  • if we alter the shape of troponin C we also alter the shape of troponin I
    - when this happens, tropomyosin gets moved either towards or away from the myosin binding site on the actin molecules

  • troponin complex: can move tropomyosin to allow contraction or to allow relaxation

  • tropomyosin (regulatory protein) which covers up the myosin binding site on the actin is an inhibitory protein
    - it prevents muscle contraction


4
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how do we cause troponin C to change shape and move tropomyosin

  • calcium

  • troponin C has a high bond to calcium
    - if we release calcium from the sarcoplasmic reticulum into the cytosol the calcium can bind to troponin C

  • this binding of calcium to the troponin C molecule causes troponin C to change shape and pulls on the other troponin molecules which then move tropomyosin and pulls it away from the myosin binding site on the thin filaments

  • C) when we expose the myosin binding site on the thin filaments, myosin can now form a cross bridge and we can begin cross bridge cycling

  • D) calcium is the molecule that stimulates the movement of tropomyosin allowing for cross bridges to form and allow for cross bridge cycling to occur


<ul><li><p>calcium</p></li><li><p>troponin C has a high bond to calcium<br> - if we release calcium from the sarcoplasmic reticulum into the cytosol the calcium can bind to troponin C</p></li><li><p>this binding of calcium to the troponin C molecule causes troponin C to change shape and pulls on the other troponin molecules which then move tropomyosin and pulls it away from the myosin binding site on the thin filaments</p></li><li><p>C) when we expose the myosin binding site on the thin filaments, myosin can now form a cross bridge and we can begin cross bridge cycling</p></li><li><p>D) calcium is the molecule that stimulates the movement of tropomyosin allowing for cross bridges to form and allow for cross bridge cycling to occur</p></li></ul><p></p>
5
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What happens if calcium is pumped out?

  • myosin cant form any cross bridges again because troponin C changed shape and allowed tropomyosin to go back and cover up the binding site on the thin filaments


6
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What is the role of calcium in muscle contraction?

  • to alleviate the inhibition of contraction