Compare and contrast microtubule assembly and intermediate f

Compare and contrast microtubule assembly and intermediate filament assembly

Solution

Answer:

Assembly of intermediate filaments:

Intermediate filaments are like ropes made up of multiple strands twisted together. The strands are made up of intermediate filament proteins.

Intermediate filament proteins, despite their variety, all have the same basic structure: they have a globular head at their N-termini, a globular tail at their C termini, and a rod-like alpha helical region in between. Two such units can wind around each other to make a \"coiled coil\" structure.

Two of these coiled coils line up head-to-tail in a staggered fashion to form a tetramer. Numerous tetramers line up end to end to make a protofilament. Eight protofilaments are wound around each other to form the rope-like intermediate filament.

Assembly of microtubules:

If intermediate filaments are like ropes, microtubules can be thought of as hollow pipes. These pipes are built of 13 parallel protofilaments, each of which is a chain of tubulin subunits. Tubulin subunits are each composed of an alpha and a beta tubulin.

These subunits stack on each other, with alpha and beta tubulin alternating, to form a protofilament that has a beta at one end and an alpha tubulin at the other. The beta end is called the plus end and the alpha end is called the minus end.

Thirteen protofilaments of this type are arranged around a hollow core, in such a way that all of them have their plus ends on the same side. This gives the overall microtubule a directionality.

Difference in assembly:

There are many differences between the microtubules and intermediate filaments, but some obvious ones are:

1. Unlike intermediate filaments all microtubules are made up of a single kind of protein called tubulin.
2. Microtubules are assembled in such a way that they have a polarity (that is, one end is different from the other).
3. Microtubules are rapidly assembled and broken down many times within a short span of time, while intermediate filaments are more stable.