Cytoskeleton I - Microtubules

Question 1

Cytoskeleton fx.

Answer 1

Cell shape, mechanical strength, structures for locomotion, support for PM, scaffold for spatial organization of organelles, intracellular transport of organelles/other cargo

Question 2

MT structure

Answer 2

hollow. Flexible but not really stretchy.
Made of alpha and beta tubulin subunits. make up protofilaments, 13 of associate laterally into spiral structure (interactions are alpha-alpha, beta-beta).
Each tubulin has GTP binding site.

Question 3

MTOC

Answer 3

One end of MT is attached to centrosome/MTOC.

Question 4

Beta end

Answer 4

Plus end, predominantly grows. GTP bearing beta subunis favor polymerization.
When you hydrolyze GTP you form a little kink that peels apart, doesn’t fall apart b/c of GTP cap.

Question 5

Alpha end

Answer 5

Minus end, disassembles.

Question 6

Treadmilling

Answer 6

GTP stabilizes it, but further in molecule it gets hydrolyzed to GDP, get disassembly.
So constant assembly/dissasembly.

Question 7

Regulation of MT

Answer 7

Capping proteins (stabilize)
Severing proteins (spastin, katanin) increase instability by exposing GDP. Cut in half so no cap. Spastin also involved in organizing MT's!

Question 8

MT fx.

Answer 8

Scaffold for spatial organization of organelles in the cell, organelle movement, cilia and flagella movement.

Question 9

Spastin Mutation

Answer 9

Severing protein.
Can be associated with hereditary spastic paraplesia.
In axons you have MT’s organized in parallel, without spastin not organized so delivery of synaptic vesicles fails.

Question 10

Katanin Structure

Answer 10

Triple ATPase. Active pore in hexamer. Tubulin has highly charged tails, the MT’s become very stable.
It pulls on the tail to unwind.
basically makes MT not straight/stable and strains tubulin interactions with MT lattice.

Question 11

Centrosome

Answer 11

Forms cilia and organizes MT’s. Gamma tubulin is not in MT’s but it forms ring around centrosome where MT bind.
Plus end face out with GTP.

Question 12

Kinesin

Answer 12

Molecular motor. Cargo towards + end. Use ATP.
Can move by hand over hand mechanism which alternates head to head. most likely.
Can move by inchworm, one head always leads.
Has 2 heads.

Question 13

Dynein

Answer 13

Cargo towards - end.

Question 14

Domains of molecular motors

Answer 14

Cargo binding domain
Motor domain (head region) hydrolyzes ATP and reversibly binds MT's.

Question 15

Mechanochemical cycle

Answer 15

MT binding, conformational change, MT release, conformational relaxation, MT re-binding.

Question 16

Mitotic spindle

Answer 16

Spindle is made of MT’s. Allows segregation of replicated chromosomes.
Motors and elongation of overlap MT’s cause growth of spindle + astral pulling –> centrosome separation
(-) end motors, kinetochore shortening, separate daughter chromos.

Question 17

Centrosome components

Answer 17

Pair of centrioles embedded in a matrix.
Nucleation sites for MT’s (rings of gamma tubulin can initiate MT pol, minus ends anchored here)
Short modified tubules + accessory proteins.

Question 18

How does motor bind its cargo?

Answer 18

There is an adaptor, where regulation probably happens.

Question 19

3 types of MT’s in cell division

Answer 19

1. ) Kinetochore (bind chromos)
2. ) Astral (radiate out, attach to cytoskeleton near mem, NOT chromos. use dynein to pull towards mem)
3. ) Overlap MT’s.

plus ends always point away from chromo.

Question 20

Cilia

Answer 20

shorter. Tend to occur in large numbers on the apical surface of epithelial cells (especially respiratory).
whip like motion, move fluids over surface.

Question 21

Flagella

Answer 21

long and serve to propel sperm with undulating motion

Question 22

Drugs that inhibit polymerization

Answer 22

Colchichine, vinblastine, vincristine

Question 23

Drugs that stabilize polymerization

Answer 23

Taxol. Causes aggregates.

Question 24

Retrograde transport

Answer 24

Probably important in development. Look I’m a neuron and I found the right target!