Eukaryotic Structure 5

Question 1

Describe microtubules structure

Answer 1

They are hollow tubes.
They are made of 13 protofilaments arranged side by side to form a hollow cylinder.
Made of alpha and beta Tubulin which form heterodimers.
There is a plus and minus end: Beta tubulin is exposed at the plus end, and alpha tubulin at the minus end

Question 2

What is microtubule dynamic ?

Answer 2

The rapid and reversible switching between growth and shrinkage at the plus ends of microtubules

Question 3

What is MT nucleation ? Describe the process

Answer 3

The initiation of a MT.
Microtubule-organising centres (MTOCs), like the centromere in animal cells, are the primary sites of MT nucleation.
1. Y-tubulin binds to the MTOC
2. Y-tubulin ring complex promotes nucleation
3. The plus end of the MT continues to grow

Question 4

What is MT polymerisation ?

Answer 4

The growth of MT that already exist.

Question 5

Why does MT shrinkage occur ?

Answer 5

1. GTP hydrolysis is faster than addition of new GTP-tubulin dimers so the GTP cap is lost.
2. Protofilaments containing GDP-tubulin peel away from the microtubule wall

Question 6

What drugs can affect MT stability ?

Answer 6

1. Taxol- stabilises tubulin in MT lattice so there is no shrinkage. It is a very potent anti-cancer drug.
2. Colchicine- binds free tubulin dimers, no MT polymerisation

Question 7

Describe the functions of MT

Answer 7

1. Structural support and cell shape- they provide rigidity
2. Intracellular transport- help move vesicles throughout the cell eg. Motor protons (kinesin and dynein) bind to MT
3. Mitotic spindle- formed by MT and attached to kinetichore. Pulls chromatids to opposite ends of the cell.
4. Motility- MT are the main structural component of cilia and flagella. Organised in a 9+2 arrangement- 9 outer MT pairs and 2 central MT pairs, connected by nexin on the outer pairs
   Dynein movement results in MT of doublets, creating beating motions.

Question 8

What is the physiological importance of cilia and flagella?

Answer 8

Cilia present on cell surface- sense and respond to exterior environment

Question 9

What are ciliopathies ?

Answer 9

Disorders associated with defects in cilia and basal body structure and intraflagellar transport
Eg. Primary ciliary dyskinesia- defects in cilia lining