Chapter 17 lecture - Cytoskeleton network of protein...

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1 Cytoskeleton network of protein filaments provides: 1. support 2. stability 3. movement three inter-linked networks: 1. actin microfilaments 7 um 2. intermediate filaments 10 um 3. microtubules 25 um each has distinct properties that help’s the cell’s structure and mechanics. Microtubules • hollow tubes, rigid, with polarity • can be long but dynamic (“dynamic instability”) • in all cells with multiple uses • originate from centrosome = MTOC (microtubule organizing center) • mitotic spindles
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2 Actin Microfilaments thin filaments, various lengths mesh-like networks & linear stretches lots and lots of them (30x more then other two) very dynamic, highly regulated cortical skeleton and elsewhere cell shape changes, contraction & movement Intermediate Filaments first discovered in smooth muscle - lots of stretching in most animal cells includes nuclear lamina tensile strength (can be stretched and return to normal) “rope-like” tough, durable, withstands mechanical stress
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3 Intermediate Filaments (IFs) IFs span cell length -sheets of cells - connect to PM via desmosomes - & cell-to-cell connections - reduces mechanical stress -Four major classes (based on cellular expression:) a) keratines b) vimentin c) neurofilaments d) nuclear lamina vary in size, aa composition especially in globular head domains keratins - epithelial cells • IF - globular head & a tail domain • central rod domain = coiled-coil interaction - very stable, strong • combine together side-to-side = “rope-like” structure with great strength non-covalent bonds form tetramer
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4 IF categories globular heads - distinct central rod conserved skin - various kinds depending on exact type of epithelial cell gut, skin, feather, claw etc accessory proteins can also act to cross-link Ifs with other filaments e.g. plectins cross-link to microtubules, actin filaments, desmosomes Microtubules long, stiff hollow tubes originate from centrosome diverse roles: a) anchor intracellular organelles b) acts as a transport network (i.e. the rails on which motor proteins work) c) mitotic spindles - cell division d) permanent microtubule based structures - cilia & flagella [note: bacterial flagella are very different] Two basic subunits very similar to each other stack together by non-covalent bonds inherent polarity: + and - ends bind to GTP and will hydrolyze to GDP at set (relatively slow) rate
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5 + end -end μ tub grow at BOTH ends by adding an alpha-beta dimer but + end >> - end Note: POLARITY
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This note was uploaded on 04/02/2008 for the course BIO 2600 taught by Professor Vanburkem during the Winter '08 term at Wayne State University.

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Chapter 17 lecture - Cytoskeleton network of protein...

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