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13 Cards in this Set
- Front
- Back
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What are the 2 groups?
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Conventional Myosin (II) and Unconventional Myosin (I, III-XVIII)
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What does Myosin II function in?
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Found in muscle cells. Also aids in formation of the cleavage furrow in animal cells. Generates tension at focal adhesions.
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Describe the unconventional myosins: 17 types
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They are grouped based on their amino acid sequence. Some are restricted in their distribution, for example, X is only in vertebrates.
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What characteristics do all myosins share?
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Domains: Head, Neck, and Tail
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Describe the Head domain.
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It is the MF binding site. And also function in ATp binding and hydrolysis. Is activated by actin
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Describe the Neck domain.
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Associated with light chains, regulate activity of the head domain. The length of the neck determines the step size of the protein.
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Describe the Tail domain.
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Highly divergent in different proteins. Provides specificity for the type of cargo transported. Also has a structural role in myosin II.
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What are the biggest differences between the myosins?
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1. Number of heads (I/2)
2. The number and type of light chains. 3. Length of the neck 4. Length, structure, and binding properties of the tails |
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Describe Myosin II
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Has 6 polypeptides: 2 heavy chains, 2 essential light chains, and 2 regulatory chains. The light and regulatory chains bind calcium. The tail, part of heavy chain, has a crucial structural role. The tails interact through coiled-coil domains to form bipolar filament.
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Describe the formation of the bipolar filament in Myosin II.
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The tail is associated with head and not free to interact. Phosphorylation of myosin light chain released the tail and exposes actin binding site. the bipolar filaments can then self-assemble.
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Describe Myosin I.
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It has only 1 head. Has a # of calmodulin light chains. Defects in this protein lead to locomotive defects. It is able to maintain tension for long periods of time without hydrolyzing ATP. Often mediates membrane-cytoskeletal adhesions which contribute to membrane tension and deformation. Involved in endocytosis/exocytosis and channel gating in the ear/sound.
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Describe Myosin V.
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2 headed. Exhibits hand-over-hand model for stepping along MF. Very stable movement, long distances.
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Describe the helix of the MF in Myosin V.
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13 monomers form 1 complete turn of the helix. The neck determines the step size. 36 nm step size is critical for stability of movement: walking a helix in shorter steps would be more difficult
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