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Actin & Myosin Interaction

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5 Terms

1

Features of Myosin

  1. Is a protein

  2. Makes up the thick filament of the sarcomere

  3. Has 2 chains that form a helix

  4. Has 2 arms and 2 heads

  • Together they form a cross bridge

  1. Heads have binding sites for ATP, and for actin and a catalytic site (ATPase).

<ol><li><p>Is a protein</p></li><li><p>Makes up the thick filament of the sarcomere</p></li><li><p>Has 2 chains that form a helix</p></li><li><p>Has 2 arms and 2 heads</p></li></ol><ul><li><p>Together they form a cross bridge</p></li></ul><ol start="5"><li><p>Heads have binding sites for ATP, and for actin and a catalytic site (ATPase).</p></li></ol>
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2
Features of Actin

Actin

  1. Is also a protein

  2. makes up the thin filament of the sarcomere

  3. Has 2 chains that form a helix

  4. Has an active site that binds myosin cross bridge

Interaction Between Actin and Myosin:

  • The active site of actin and myosin bind

  • The ATP allows the crossheads of myosin to move the actin towards M-Line.

<p><strong>Actin</strong></p><ol><li><p>Is also a protein</p></li><li><p>makes up the thin filament of the sarcomere</p></li><li><p>Has 2 chains that form a helix</p></li><li><p>Has an active site that binds myosin cross bridge</p><p></p></li></ol><p>Interaction Between Actin and Myosin:</p><ul><li><p>The active site of actin and myosin bind</p></li><li><p>The ATP allows the crossheads of myosin to move the actin towards M-Line.</p></li></ul>
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3
Tropomyosin

Tropomyosin is another protein that is important to understand, as it allows for the regulation of the actin-myosin interaction:

Tropomyosin: Protein that covers the actin active site

  • When tropomyosin is attached there is no binding of actin and myosin.

  • Thus, there is no sarcomere contraction (and thus no muscle contraction).

<p>Tropomyosin is another protein that is important to understand, as it allows for the regulation of the actin-myosin interaction:</p><p>Tropomyosin: Protein that covers the actin active site</p><ul><li><p>When tropomyosin is attached there is no binding of actin and myosin.</p></li><li><p>Thus, there is no sarcomere contraction (and thus no muscle contraction).</p></li></ul>
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4
Troponin

Troponin: Protein that removes tropomyosin

  • This allows the actin and myosin to bind again.

  • This allows the muscle fibril, fibre and entire muscle to contract.

  • Troponin is recruited by Calcium: when calcium arrives -→ signals Troponin to come - moves Tropomyosin - frees Actin - allows Sarcomere to contract.

<p>Troponin: Protein that removes tropomyosin</p><ul><li><p>This allows the actin and myosin to bind again.</p></li><li><p>This allows the muscle fibril, fibre and entire muscle to contract.</p></li><li><p>Troponin is recruited by Calcium: when calcium arrives -→ signals Troponin to come - moves Tropomyosin - frees Actin - allows Sarcomere to contract.</p></li></ul>
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5
Take Away Points

  1. Actin and myosin have active sites that bind.

  • The myosin pulls the actin filament towards M-Line using ATP.

  1. Tropomyosin ensures that this process is not continuous.

  • Does this by blocking the actin-binding site.

  1. Troponin is able to remove the tropomyosin to allow for the binding.

  • It is recruited by calcium.

  1. Thus an influx of calcium is what allows muscles to contract!

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