Question

what are the major components of the cytoskeleton? Explain each by listing.

Answer 1

Cytoskelton is a network of protein fibers which provides shape and maintain cell structure. It also provides anchor for cell organelles and helps in cell movement. There are three major components of cell cytoskeleton - microtubules, actin filaments, and intermediate filaments.

1. Microtubules

Microtubules are rigid and hollow rod strutures.

It is a filament (polymer) of tubulin monomers. alpha and beta tubulin heterodimer polymerise into long protofilament.

This protofilament has plus end and minus end.

11 to 15 protofilaments arrange into microtubule structure.

Beta subunit is exposed to plus end (fast growing end) and alpha subunits are exposed to minus end (slow growing).

One GTP binding site is present on both alpha adn beta subunit of tubulin.

Tubulin molecules carrying GDP bind to one another with higher affinitythan tubulins carrying GDP.

GDP bound beta tubulin is more prone to depolymerisation.

Microtubules participate in intracellular transport of cargos (organelles and vesicles).

Colchicine binds tubulin subunits and prevent polymeristaion of subunits into microtubules.

2. Actin Filaments

It is made up of G-actins (monomers).

G-actin has binding site for ATP.

G-Actin subunits also arrange into filamentous F-actin.

Two parallel F-actin twist together to form actin filament in right hand helix manner.

Therefore, it is much more thinner and flexible than microtubules.

It has also plus and minus end. Plus end polymerise or grow ten times faster than minus end.

Phases of polymeristaion are - nucleation phase, elongation phase and steady state phase.

Drug Cytochalasin D binds to plus end of actin filaments and prevents the elongation.

Actin filaments are abundantly present beneath of plasma membrane and involved in maintaining cellular structure, shape and also in cellular movement.

3. Intermediate Filaments

It is a filament of rope like structure and are about 10nm in diameter.

It is called intermediate because the the diameter is intermediate between diameter of other two main filaments i.e. Microtubules and Actin Filament.

They do not involved in cell motility unlike other two filaments.

It is an elongated molecule with non alpha helical N terminal head domain, central alpha helical rod domain and a non alpha helical C terminal tail domain.

This is how intermediate filaments are formed:

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