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Unformatted text preview: Microfilaments Microfilaments Structure Flexible, helical fibres of ~7 nm diameter G-actin Central cavity binds ATP or ADP F actin 37 + end (faster growth) BIO 1140 – SLIDE 1 F-actin Polymer of G-actin monomers Helix Filament has polarity Fig. 2.22- end G-actin + ADP Dissociates readily G-actin + ATP Polymerizes readily Dynamic character ATP-G-actin polymerizes more readily than ADP-G-actin Hydrolysis follows polymerization ADP-G-actin dissociates more readily than ATP-G-actin Treadmilling Actin-binding proteins regulate the rate and form of polymerization and BIO 1140 – SLIDE 2 Fig. 9.65, Karp et al. 2010 network formation Cell signalling mechanisms regulate actin-binding proteins Useful drugs Cytochalasin Phalloidin Functions Shape/support Cell cortex - networks Microvilli - bundles Adherens junctions BIO 1140 – SLIDE 3 Fig. 15-18, Becker et al. 2009 Fig. 17-2, 17-29, Alberts et al. 2004- smallest set of skeletal element- supermolecular structure - complex of proteins- building block is monomer of actin- many diff isoforms of actin - highly conserved-- can take actin from two different species and they can polymerize together- actin takes U shaped form- link to other actin monomers- link the same way - gives polarity - - end--- + end is where the microfilament grows - new monomers are added there- two helices wind around each other- monomer of actin - is called G-actin-when stringed together - called F-actin- if ATP is bound to G-actin - polymerizes more quickly --- more likely to be hydrolyzed to ADP-G-actin- once hydrolyzed will be more readily dissociated- monomer sequestering proteins - decrease the likelihood of getting a microfilament- microfilament - more likely to form spontaneously compared to microtubules- proteins that cap the + end - prevent it from growing- protein that help microfilament form arrays or bundles- proteins that bind the filament to the cell membrane- also proteins that depolymerize the filament Cytochalasin - monomer sequestering compound - prevents actin from polymerizing - higher likelihood of microfilaments breaking down--- has similar effect on filaments that Choloisin has on microtubules Phalloidin - stabilizes microfilaments - comes from deathcap fungus --- same effect on filaments that Taxon has on microtunules---- both from fungus- cell cortex - important in supporting cell membrane - often linked to cell membrane to provide supporting structure-- particularly in animal - but can also be found in some organisms with cell walls ex. fungi- microvilli - fingerlike extensions from the cell...
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This note was uploaded on 03/26/2012 for the course BIO 1140 taught by Professor Fenwick during the Winter '07 term at University of Ottawa.
- Winter '07
- cell biology