cell cytoskeleton
- Created by: Amber Manley
- Created on: 14-01-14 17:49
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- cytoskeleton
- Basics
- cell's skeleton
- filamentous structure found throughout the cell
- protein monomers that assemble into repeat structures
- dynamic - assembles and disassembles to suit cell
- 3 types of filament
- actin
- microtubules
- intermediate filament
- Actin Filaments
- globular protein actin
- assembles into double stranded helical polymers
- concentrated beneath cortex
- cell shape and motility
- microtubules
- globular protein tubulin
- dimerize and form hollow tubes
- more rigid
- attached to microtubule organising centre (centrosome)
- other ends grow and shrink around this centre
- positioning organelles, intracellular transport and mitosis
- intermediate filaments
- various intermediate proteins, filamentous themselves
- extended a helical regions that wind together
- form rope like structure
- mechanical support of cell
- lamins nuclear lamina
- Assembly
- monomers form end-to-end and side-to-side interactions
- interactions aren't covalent
- easier to disassemble/assemble
- disassembles at a constant rate
- assembly relative to monomer conc
- critical concentration of monomers where they're equal
- cytoskeltal elements will grow until equilibrium is reached
- auxiliary proteins can affect these processes
- Confirmational Change
- actin and microtubules have fast and slow growing ends
- subunits attach to fast end, confirmational change occurs, readying for next monomer
- fast end has higher affinity for monomers than slow end
- Nucleotide Hydrolysis
- actin monomers carry ATP
- Actin ATP has high affinity for actin polymer
- after attachment, ATP forms ADP
- tubulin carries GTP
- Accessory Proteins
- dynamic control of filaments
- nucleation
- auxiliary proteins may act as initiator for new filaments
- assembly
- proteins which bind monomers change concentration
- disassembly
- proteins bind, either stabilise or destabilise filaments
- nucleation
- link other cellular components to cytoskeleton
- motor proteins move organelles along filaments
- dynamic control of filaments
- Motor Proteins
- myosins
- actin based motor proteins
- myosin II - muscle contraction
- 2 myosin II chains wind together to form a long tail domain
- tail domains can interact with other chains
- form large bipolar thick filaments, hundred of myosin heads
- Attached - myosin head binds actin filament
- Release - myosin binds ATP, releases actin
- Cocked - ATP hydrolysis and confirmational change
- Grip - reattachment to actin and phosphate release
- Pull - confirmational change and ADP release
- Muscle Units
- sarcomeres arranged in long repeating chains (myofibrils)
- thin and thick filament areas
- slide theory
- don't lose length, sarcomere shortens though
- Kinesins and Dynesins
- microtubular motor proteins
- kinesin slow to fast end
- dynasin fast to slow
- most have 2 globular heads that use ATP hydrolysis to function
- Kinesins
- Leading head bound to tubulin
- trailing head bound to ADP
- confirmational change as head 1 binds to ATP
- throws head 2 forward
- head 2 binds tubulin
- head 2 release ADP; head 1 hydrolyses ATP
- back to beginning
- myosins
- cell motility
- cell crawling
- macrophages/neutrophils
- rearrangement of actin skeleton
- protrusion
- actin fibres fom at leading end
- attachment
- attaches to surface across cell membrane
- traction
- cytoplasm pulled
- flagella and cilia
- microvilli
- cell crawling
- Basics
- concentrated beneath cortex
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