Microbiology: microtubules Flashcards
Properties and functions of the cytoskeleton (inclusive of which microfilament proteins)?
- Dynamic but organised structures
- Formed from the polymerisation of small subunits
- Provide cellular structure and organisation
Function
Intermediate filaments
- cell strength + mechanical support
Actin
- Cell structure and shapoe
- cell migration
Microtubules
- organisation of intracellular structures and organelles
- intracellular vesicle trafficking
- chromosome segregation during mitosis
- cell polarity
- formation of cilia and flagella
Microtubule structure
- comment on GTP biding sites
- polarity
alpha/beta-tubulin dimers wrapped into a 13 protofilament hollow tube
- both capable of binding GTP
- GTP/GDP binding site on Beta-tubulin is exposed
- alpha-tubulin GTP binding site is blocked by Beta-tubulin
- Polarity, tubules have ‘plus’ and ‘minus’ ends
- alpha side is minus, beta side is plus
- this is due to molecule shape, not charge
- new dimers are added to plus end, removed from minus end
Which organelle is the major microtubule organising centre (MTOC) of a cell
Centrosome
Describe centrosome-microtubule structure
Microtubules nucleate from centrosome
- grow from gamma-tubulin ring complex on centrosome surface
- In vivo, microtubule minus end is anchored and protected at centrosome
- plus end dictates interactions
Microtubule dynamics are powered by which process
- comment on shrinking and growing
GTP hydrolysis
- if GTP is bound, microtubule is stable -> growing
- GTP cap stabilises + end
- GTP hydrolysed to GDP, filament becomes unstable and ‘bent’ -> shrinking
Hydrolysis dictates catastrophe and rescue (dynamic instability)
Importance of dynamic instability
Allows for rapid reorganisation in response to appropriate cell stimuli
Which fascillitating proteins also regulate microtubule dynamics
- describe function
- give examples
MAPs -> microtubule associated proteins
- Bind either along the sides or at the ends to
- stabilise filaments
- destabilise filaments
- link filaments to other molecules
Regulate growth/depolymerisation
e.g. Tau protein family, Kinesin-13
Microtubule motor protein function
- 2 types
- which direction do they move
Act as ‘tracks’ along which organelles/vesicles are moved
Kinesins -> + end
Dyneins -> - end
Which process allows Kinesin and Dynein to move?
Movement due to conformational change upon ATP hydrolysis
Dynein has additional dynactin complex to link motor protein cargoes
Example of a cell where microtubules contribute to cell polarity
In epithelia
- Plus end towards basolateral domain
- Minus end to Apical domain (with microvilli) -> leading edge
Which drug is often used to depolymerise microtubules?
Process?
Nocodazole
- binds to free alpha/beta tubulin dimers and prevents their incorporation into growing microtubules
- catastrophe occurs -> no rescue
