The Cytoskeleton

Spread out through the cytoplasm of eukaryotic cells.

Contains Actin filaments + Intermediate filaments + Microtubules.

Actin filaments = made up of twisted chains of the protein actin. Provide cell movement + cell division. More concentrated inside the plasma membrane where they are arranged into a network to provide strength. They are continuously growing + shrinking.

Intermediate filaments = Rope-like fibres of 8 protein strands twisted together. Provide cell shape + mechanical strength.

Microtubules = made up of alpha-tubulin and beta-tubulin. Hollow tubes of protein. Provide internal cellular organisation + transport + specialised structures.

Microtubules form tracks through the cell, scaffold-like structure. Motor proteins walk along these Microtubules.

Motor proteins :

Kinesins carry organelles away from the centrosome. Dyneins carry organelles towards the centrosome.

Motor proteins transport molecules around the cell in vesicles consisting of a lipid bilateral membrane surrounding a fluid interior.

Vesicles carry hormones to the plasma membrane for secretion from the cell.

For example, the ER is held in place by motor proteins. Kinesins pull the ER along Microtubules away from the nucleus, spreading it like a net. Dyneins pull the ER back towards the nucleus. The tug-of-war allows the ER to be distributed throughout the cell.

Cell migration = movement of cells over a surface.