The Muscle Fiber

A.) A protein microfilament responsible for the contraction of a muscle cell.
b.) Composed mainly of myosin or actin.

A.) Each is made of several hundred molecules of myosin.
b.) "Golf club" heads on one half are angled to the right; on the other half they're angled to the left; and have no heads in the middle, which is called a bare zone.

A.) A protein shaped like a golf clube, with 2 chains intertwined to form a shaftlike tail & a double globular head projecting from it.
b.) Found in thick filaments.

A.) Composed mostly of 2 intertwined strands of fibrous (F) actin.
b.) Also composed of 40-60 molecules of tropomyosin.

A protein composed of a string of subunits called globular (G) actin.

A spherical-shaped protein with an active site.

The region of G actin that can bind to the head of a myosin molecule.

A.) A protein that, when the muscle fiber is relaxed, blocks the active sites of 6 or 7 G actins & prevents myosin from binding to them.
b.) Each molecule has troponin bound to it.

A smaller, calcium-binding protein.

A.) Made of a huge, springy protein called titin (connnectin).
b.) They flank each thick filament & anchor it to a structure called the Z disc.
c.) Helps stablilize the thick filament, center it between thin filaments, & prevent overstretching.

A dark band formed by parallel thick filaments that partially overlap the thin filaments causing the dark striations.

A light band composed of thin filaments only.

A protein disc that bisects each light I band & provides anchorage for the thin filaments & elastic filaments at the ends of sarcomeres that appears as a narrow, dark line in the middle of the I band.

A.) The distance from one Z disc to the next.
b.) The functional contractile unit of a muscle fiber.
c.) Causes a muscle to contract by shortening & pulling the Z discs closer to each other.

A tunnel-like extension of the sarcolemma extending from one side of the muscle fiber to the other that conveys electrical signals from the cell surface to the interior.