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Intermediate Filaments note

Intermediate Filaments note - Cytoskeleton II Intermediate...

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Cytoskeleton II: Intermediate Filaments (Lodish Chapter 18) I. Intermediate filaments (Lodish Fig. 18-44, 45) A. Named because of their thickness (10 nm), which is intermediate between actin filaments (7 nm) and microtubules (24 nm). Found in animal cells but not in plant and fungi. B. In epidermal cells and the axons of nerve cells, IFs are 10x more abundant than microfilaments or microtubules. C. Different from the other two classes of filaments 1. More stable 2. Form α -helical rods 3. Subunits don’t bind NTPs: a. Don’t appear to contribute to cell motility (structural role only) b. No IF associated motor proteins found. D. IF domain structure 1. IF proteins form dimers and then tetramers (Lodish Fig. 18-33a & b, Alberts Fig. 16-17) a. Dimers in a tetramer have an antiparallel orientation. b. Tetramers then associated into protofilaments and then protofibrils, which are then compacted into mature filaments (Lodish Fig. 18-33c) c. No known polarity 2. Most of the IF protein in a cell is in filaments, the remainder (1-5%) is in tetramers 3. Tetramers are thought to be the building blocks of IFs.
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