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42 Cards in this Set
- Front
- Back
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the fibers of skeletal muscle are said to be _____ rather than composed of individual cells
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syncytial - multinucleated mass of cytoplasm; not a traditional cell
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Syccytium/Syncytial
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refers to the muscle fibers of skeletal muscle with many peripheral nuclei
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Sarcolemma
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the plasma membrane for an individual muscle fiber
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Sarcoplasm
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the cytoplasm of a muscle fiber
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Sarcoplasmic reticulum
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the (smooth) endoplasmic reticulum [cisternae] specific to skeletal muscles that runs parallel to the myofibrils and wraps each one
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Myofibril
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the organelle that runs along the length of each muscle fibril in the sarcoplasmic matrix
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Transverse Tubule (T-Tubule)
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tubules which run perpendicular to myofibrils and connect between the sarcoplasmic reticulum and the sacrolemma (sarcolemma extenstions); also correspond to Z-lines
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running down the length of one myofibril, you will alternate between...
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light bands (I-band) and dark bands (A-band)
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the I in I-Band stands for
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isotropic - because there is only actin
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the A in A-Band stands for
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anisotropic - because you may find both actin and myosin
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Z-line
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the dark line in the middle of the [light] I-band; actin myofilaments are attached; also falls underneath T-tubules
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H-Zone
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a pale area in the [dark] A-band; where the myofilaments do not interdigitate
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M-line
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a dark line in the middle of the [pale] H-Zone
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Sarcomere
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the basic unit of muscle contraction which repeat end to end to make up a myofibril; also the distance between two sucessive Z-lines (or T-tubules) slightly less than 3 micrometers
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The 2 proteins which make a myofibril
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Actin & Myosin
there is twice as much actin as there is myosin |
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Myofibrils are made of interdigitated _____
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myofilaments
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The I-band is light because it corresponds with which myofilament?
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The actin or thin myofilaments
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The A-band is dark because it corresponds with which myofilament?
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The myosin or thick myofilaments
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A trasverse cross-section of a myofibril will reveal a _____ arrangement of myofilaments
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hexagonal
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I-band
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band consisting of actin myofilamnets which have a z-line
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A-band
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wide dark region of overlapping actin and myosin; contains an H-zone (no actin)
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Cross-bridges
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proteins which stick out at the ends myosin filaments and facilitate the powerstroke involved in muscle contraction
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In muscle contration describe what happens to (1) the A-band, (2) the I-band and (3) the H-zone.
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(1) A-band remains the same length
(2) I-band shortens (3) H-zone reduced or disappears |
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Proposed the Sliding Filament Theory to explain muscle contraction. [2]
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Andrew F. Huxley & Hugh E. Huxley
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Which of the myofilaments get shorter during muscle contraction?
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Neither. The sarcomeres shorten due to an overlap of the myofilaments.
This also describes the Sliding Filament Theory. |
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1 Myosin filament is made of how many myosin polypeptides?
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200-300 myosin II polypeptides
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The two regions of a myosin II polypeptide.
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Compact head and a long tail region of 2 α-helices
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the tail of a myosin II polypeptide is made of
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two α-helices, each helix is a heavy chain with 2000 amino acids
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Each heavy chain in myosin II polypeptides has a _____ at its N-terminus
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globular head domain (in groups of 3)
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Each globular head has ______ closely attached. What purpose do these have?
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two light chains attached to each head which form cross bridges (with actin filaments)
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each head is known as an ___ acts as an _____
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S1 acts as an ATPase that binds and hydrolyzes ATP
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3 components of actin filament
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F-Actin
Tropomyosin Troponin [3 proteins] |
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F-actin is controlled by...
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Tropomyosin and troponin
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The 3 globular proteins which compose troponin...
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TnC, TnI, TnT periodically attached to the tropomyosin strand
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F-actin
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a double stranded protein molecule actin wound into a double helix
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Tropomyosin
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a double stranded α-helical protein molecule lying in the groove of the F-actin helix
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Troponin (Complex)
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3 globular proteins periodically attached to the tropomysoin strand
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This globular protein in actin binds to tropomyosin [1]
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TnT
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This globular protein in actin bind to both F-actin and TnT in troponin
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TnI
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This globular protein in actin binds to calcium ions
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TnC
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Ratchet Mechanism of Contraction
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describes the biochemical and biophysical events which occur during muscle contraction
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Briefly describe the process of the Ratchet Mechanism
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ATP molecule energy is converted into physical work in the form of myofilament displacement (sliding)
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