The Cytoskeleton Flashcards
Three classes of filaments
Actin
Interm mediate filaments
Microtubules
What is f-actin, what is it made of
Filamentous actin
Made of G actin (globular actin)
Actin structure
Polarised double helix
Diameter= 7nm
13 subunits per turn
Actin filament growth
ATP hydrolysis to ADP as soon as incorporation occurs
Removed or added from both ends
Added more rapidly to +ve end
Actin functions
1, mechanical support
- Cell shape changes/maintenance
- Cell motility
Intermediate filament structure
Polymers of individual IF proteins
10nm in diameter
IF location and function
Most dense around nucleus, extends to periphery
Anchor cell at cell junction
Support nuclear structure
IF growth
2 IF protein -> helical dimer
2 helical dimmers-> 1 tetramer (fundamental unit)
Tetramers link -> Staggered formation
What links IF to actin and microtubules
Plectin
Microtubule structure
Stiff hollow tube of 13 tubulin monomers Diameter= 25nm Rapidly assembles & disassembled Alpha and beta tubulin Has polarity (one end has alpha; other end beta)
Growth of microtubule
GTP-> GDP : removal of monomers from -ve end
GDP-> GTP: addition of monomers to +ve end
Where are microtubules polymerised
In centrosomes.
-ve end stays close to centrosome
+ve end points towards cell periphery
Examples of how actin affects cell shape and orientation
Dense sheets of actin in cell cortex
- Microvilli
- RBC
- stereocilia: actin keeps stereocilia rigid-> cells are polarised/depolarised by deflections caused by sound
Example of how IF affects cell shape and orientation
Stabilises axon shape
Example of how microtubules affect cell shape and orientation
Platelets/axons