BRAINCAKEActin
Myofibrils are made from two types of protein filaments (myofilaments), the thinner actin filament and the thicker myosin filaments. The monomer G-Actin (globular) forms a linear polymer F-Actin (filamentous) which forms two helices that spiral round each other. Actin filaments have myosin binding sites which are blocked by rod-shaped proteins called tropomyosin. Tropomyosin is held in place by a the Troponin complex. This is a globular protein with 3 subunits. The I subunit binds to actin and the T subunit binds to tropomyosin. The C subunit binds to calcium ions.
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Key terms in this lesson
- myofibril
- A long, cylindrical, rod-like organelle within a muscle fibre, made of actin and myosin filaments, that is the contractile element of the fibre.
- myosin
- A thick protein myofilament with a hinged globular head that binds to actin and ATP and pulls actin filaments during muscle contraction.