Dynamic instability of microtubules

What are microtubules?

Cylindrical tubes made of tubulin proteins; part of the cytoskeleton that supports cell shape, transport, and division.

What are the two ends of a microtubule?

Plus end (+) – dynamic, grows and shrinks quickly; Minus end (−) – usually anchored, less dynamic.

What is dynamic instability?

The rapid switching of microtubules between growth and shrinkage at their plus ends.

What is microtubule growth?

Addition of tubulin proteins at the plus end, making the microtubule longer.

What is microtubule shrinkage?

Loss of tubulin proteins from the plus end, making the microtubule shorter.

What is catastrophe in microtubules?

Sudden switch from growth to shrinkage.

What is rescue in microtubules?

Sudden switch from shrinkage back to growth.

What is the role of GTP in microtubules?

GTP-tubulin is stable and promotes growth; it acts like a “charged battery.”

What is GDP in microtubules?

GDP-tubulin is unstable and promotes shrinkage; it acts like a “dead battery.”

What is the GTP cap?

A layer of GTP-tubulin at the microtubule tip that stabilizes it and prevents shrinkage.

What happens when the GTP cap is lost?

The microtubule undergoes catastrophe and starts to shrink.

Why is dynamic instability important for cells?

It allows cells to reorganize their structure, explore space, and properly divide chromosomes during mitosis

Give an analogy for microtubule growth and shrinkage.

Microtubule tip = rope: strong tip (GTP) grows, weak tip (GDP) shrinks, sometimes collapses (catastrophe) and grows again (rescue).

What are the key parameters used to describe microtubule dynamics?

Growth rate, shrinkage rate, catastrophe frequency, and rescue frequency.

GTP

Guanosine Triphosphate

Has 3 phosphate groups and stores energy

GDP

Guanosine Diphosphate

Has 2 phosphate groups
Has less energy and doesn't stabilize the microtubules

The role of tubulin in microtubules

Tubulin proteins carry GTP when they are free in the cell.

When tubulin adds to a microtubule, the GTP gets slowly converted to GDP.
So, the GTP cap at the microtubule tip keeps it growing, and losing that cap triggers shrinkage