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
Example of how actin anchors organelles
Holds synaptic vesicles near presynaptic membrane
Example of how microtubules anchor organelles
They organise ER
Actin-based cell movement
- Actin filament polymerisation-> cell protrusion
- focal contact junctions allow adherence between surface cell is moving through and F actin
- Cell pulls against anchorage points to drag itself forward
- Depolymerisation at rear
Lamellopodia mechanism/function
Made from rapid growth of actin
+ve end towards periphery
Attachment to extracellular, matrix by focal adhesions
Exploratory and motile
Samples environment
Extends and withdraws
Interaction between myosin and actin that allow for cell movement
- ATP attaches to myosin-> myosin binds to actin
- ATP hydrolysed -> myosin tail moves
- ADP released-> myosin head detaches
- ATP reattaches-> head binds further down actin
Microtubule based movement and associated protein
Cilia/flagella
9+2 arrangement of microtubules
Dynein: minus-end directed motor protein
Example of how microtubules move intracellular contents/organelles
Microtubules move synaptic vesicles along axons to synapses
2 associated motor-proteins…
Kinesin: moves towards +ve end (cell periphery)
Dynein: moves towards -ve end (near nucleus)
Cell div
Kinesin features
Processive motor protein-> attached to microtubule throughout
Movement requires ATP
10cm per day
Examples of chemotherapeutic agents that disrupt cytoskeleton. How do they do so
Vinblastine/colchicine/taxol
V+c destabilise microtubules
Taxol stabilises microtubules
All 3 inhibit mitosis spindle and cell division
2 examples of actin-related cytoskeleton diseases
- Mutations in dystrophin -> duchenne and Becker muscular dystrophy
- mutations in myosin VII-> ushers syndrome (deafness and blindness)
2 examples of IF-related diseases
- Mutations in keratin-> blistering/sloughing-> Epidermolysis bullosa symplex
- Mutations in meurofilamin genes -> ALS
2 examples of microtubule-related disease
- Alzheimer’s: neurofibrillary tangles-> Tau is hyperphosphorylated-> can’t bind microtubules
- Hereditary spastic paraplegia: mutations in spastin (severs microtubules)
Listeria bacteria mechanism
Listeria engulfed-> escapes phagocytic vesicle-> f actin polymerised at back of bacterium-> bacterium comet-ed into neighbouring cell
