GET MILLARED Flashcards
(1) Structure of Microtubule
- Dimers of A-tubulin and B-tubulin
- GTP bound dimer is added to MT
- Each photofilaments has alternative A-Tub and B-Tub
- 13 parallel protofilaments which form MTs (forms lumen)
(1) Gamma-tublulin waht do?
Major component of gamma-tubulin ring complex, recruited to MT organising centres (centrosome)
(1) Formation of MTs
- MTs only form when above threshold concentration (Critical concentration)
- Crit conc at +ve end is lower than -ve end, MTs grow at +ve end.
(1) WAT is treadmilling
- Negative end allowed to disassemble while the +ve end assembles.
- Rate of polyermisation and depolyerisation is the same, polymer stays the same length. (causes MT flux to occur)
(1) WAT does Taxol do?
Blocks mitosis by stabilising MTs, but doesn’t block other functions of MTs
(1) WAT does Colcemid do?
Binds to tubulin dimer and prevents polymerisation. Blocks mitosis by dissolving spindle
(1) WAT does Nocodazole do?
Binds tubulin dimer and prevents polymerisation
(1) Outline the animal cell MTOC
Centrosome
- MTs are nucleated by gamma-TURs
- Gamma-tubulin prevents poly from -ve end of MT
- Negative end is near MTOC and +ve end is near cell pheriphery
(1) What do MTs do during interphase
- Positive ends directed to cell cortex where they interact with plasma membrane
- Allows MTs to maintain cell shape
(1) Effect of GTP to GDP hydrolysis in B-tubulin
- Conf change that tenses lattice
- GTP dimer has 5 degree straight angle (MT assembly)
- GDP dimer has 12 degree bent heterodimer angle (MT disassembly)
- Cap stops depoly
(1) Outline process of dynamic instability
1) Rapid growth with GTP cap
2) Due to the slow hydrolysis of GTP to GDP in B-tubulin, the GTP cap is lost (catastrophe)
3) Rapid shrinkage
4) Regain of GTP-cap (rescue, modulated by MAPs)
5) Repeat
(1) What happens to MT during mitosis
- Spindle MTs undergo MT flux (-ve end can now undero deploy at spindle poles)
- Helps form bi-oritentation during pro-metaphase
- MT length remains constant
(1) 3 types of single MTs
1) Astral MTs: Link spindle pole to cell cortex
2) Interpolar MTs: Inter-digitate at centre of spindle
3) Keinetochore Mts (k-fiber): Connect spindle polesat chromosome at kinetochore
(2) 2 Examples of MAPs
1) EB-1: Only binds GTP-tubulin (Stabilises the MT seam and is present on growing end of MT)
2) DASH-ring complex: Binds poly and depoly (couples kinetochore movement to MT depoly)
(2) 2 examples of cross-linking, stabilising, bundling proteins
1) MAP2, Tau: Binds side and stabilises parallel MTs (via promoting poly or inhibiting MT catastrophe)
- Space between MTs is greater with MAP2 than Tau expressing cells
2) MAP65: Bundles and stabilises anti-parallel MTs (key in bi-polar spindle)
- MAP65 both MT binding and dimerisation domains
(2) 2 types of MT motor proteins
1) Kinesin
- These are plus end directed motors (kinesin-14 is ive end motor)
- Use ATP to generate force
- Direct exocytosis
2) Dynein
- Fast -ve end direct motor
- Uses ATP to generate force
- Direct endocytosis
(2) Process of kinesin movement
1) Forward motor binds B-tubulin, releasing ADP
2) Forward head binds ATP
3) Conformational change in neck linker causes rear head to swing forward
4) New forward head releases ADP, trailing head hydrolyses ATP and releases Pi
(2) Cargo of kinesin motors
1) Organelles: ER and Golgi
2) Secretory vesicles: Mediation of exocytosis
3) MTs: sliding kinesin (5+6) used in anaphase of mitosis
4) Chromosomes (mitosis)
(2) Cargo of dynein
1) Direct endocytosis
2) Late endosomes, lysosomes, golgi positioning
(2) Differences between the 3 MT structures
1) Singlet: Simple tube, 13 protofilaments, flexible
2) Doublet: A + B tubule, cilia/flagella, less flexible
3) Triplet: A, B, C tubules, basal bodies/ centrioles
(3) Where is ATP binding cleft on actin
ATP binds to opposite of adjoining actin molecule.
Gives filament polarity with actin binding cleft exposed at -ve end.
(3) How F-actin filaments form
- When conc of G-actin is larger than Cc, filament gets longer
- When conc of G-actin is smaller than Cc, filament will disassemble
(3) Process of G-actin addition
- Rate of additon of ATP G Actin is 10X faster at +ve end than -ve end, dissocation rate similar
- ATP hydrolyses to ADP-Pi, Pi released slowly. Filament has ATP, ADP-Pi and ADP actin
- Treadmilling effect caused by adding ATP actin at +ve end.
(3) Function of thymosin-B4
-Binds to G-actin, cannot be added to filaments. (As conc of G-actin is 1000X more conc than Cc)