Troponin is one of the protein molecules that (together with myosin, actin, and tropomyosin) forms the cylindrical structures called myofibrils that, together, form muscle fibres.

Myofibrils consist of two types of protein filaments, called thin filaments and thick filaments. Troponin molecules, together with tropomyosin and actin molecules, form the thin filaments which have a helix structure - as shown in the diagram below.

Above: Diagram of troponin molecules within a thin filament

Troponin acts in combination with tropomyosin to control muscle contraction.

  • During muscle relaxation, troponin holds tropomyosin in position covering myosin-binding sites on actin proteins. (The protein myosin is part of the thick filaments of muscle fibres.)
  • During muscle contraction calcium ions (Ca2+) bind to troponin, changing the shape of the troponin-tropomyosin complex and therefore uncovering the myosin-binding sites on the protein actin - which is part of the thick filaments of muscle fibres.

See more about the types of muscle contraction.

This section consists of short summaries about the structures that form the muscles of the body. This list is not exhaustive but is intended to be appropriate for students of A-Level Human Biology, ITEC courses in massage and related subjects, and other courses in health sciences. For more general information about muscles see the pages about:

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