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sarcoplasmic reticulum is an organelle found only in
muscle cells
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muscle cells are multi-nucleated and are called
muscle fibers
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calcium ions bind to this to lead to muscle contraction
troponin
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troponin binds to this to lead to muscle contraction
calcium ions
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calcium ions are released into the cytosol from this organelle
sarcoplasmic reticulum
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muscle fibers contain myofibrils composed of arrays of
filaments
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myofibrils are
cylindrical bundles within the muscle cells (within the muscle fibers)
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the filaments within myofibrils within muscle fibers (muscle cells) are arranged this way
in a repeating pattern
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one repeat of the pattern of the filaments within the myofibrils is called the
sarcomere
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thick filaments are made of
myosin
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thin filaments are made of 3 proteins that regulate contraction, called
actin, troponin and tropomyosin
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myosin is a
motor protein
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actin is a
cytoskeletal protein
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the wide, dark "A" band is composed of the
thick filaments
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sizewise, the thin filaments are
half the diameter of the thick filaments
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each muscle fiber behaves as
a single unit
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each muscle fiber is multi-
nucleate
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each muscle fiber contains these
myofibrils
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the banding pattern seen in striated muscle are actually the repeating units of
sarcomeres
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a myosin thick filament has a heavychain tail and this many heads
two
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troponin is a complex of 3 proteins:
troponin I, troponin T, troponin C
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-
-
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a thick filament has 2
a thick filament has 2 heads
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a thin filament is made of the
3 troponins (composed as "troponin") wound around with actin, and tropomyosin
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tropomyosin is
a filamentous protein that runs along the groove of each twisted actin filament
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myosin makes up these filaments
thick
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actin makes up these filaments
thin (along with tropomyosin and the 3-part troponin)
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this textbook arrangement of the thin filament is present when a muscle is
at rest
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in order to contract, this must get out of the way of the actin
tropomyosin
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once tropomyosin gets out of actin's way,
actin (thin) and myosin (thick) can interact. actin has sites for myosin to bind
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when the muscle is at rest, the myosin-binding sites on the actin are covered by
tropomyosin, so that actin and myosin cannot interact
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in order to contract, actin (thin) and myosin (thick) must
interact
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