Biology II - Muscular Systems: Structure of a Myofilament

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Biology II

4 Terms

1
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myosin

thick myofilament

many myosin heads that bind to actin

powered by ATP

lift when contracted

2
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actin

thin myofilament

made of 2 actin myofilaments twisted together (2 strands of pearls)

had myosin-binding sites

2 regulatory proteins (tropomyosin and troponin)

3
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tropomyosin

rod-like

stiffens and stabilizes actin (actin is like wet noodle)

blocks myosin binding sites when a muscle is relaxed

4
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troponin

globular protein

made of 3 subunits

1 subunit binds to actin (I)

1 subunit binds to tropomyosin (T)

1 subunit binds to calcium ions (C)

when a calcium ion binds to troponin, it pulls tropomyosin off the myosin-binding sites of actin (so myosin can bind to actin and cause contraction)