AH Biology: Unit 1

The Cytoskeleton

A cell must arrange itself in three-dimensional space and interact physically with its surroundings.

How many cell structures and processes can you identify in the Inner Life of the Cell animation?

The cytoskeleton

• An intricate and interconnected system of protein filaments that extends from the nucleus to the plasma membrane.

• Found exclusively in eukaryotic cells.

Roles of the cytoskeleton

- Provides a framework of mechanical support to a cell, which allows it to maintain its shape.

- Allows the movement of cell organelles.

- Allows the movement of whole cells, eg white blood cells and amoebae.

Roles of the cytoskeleton in cell division

­Responsible for the movement of chromosomes during the processes of meiosis and mitosis.

­Responsible for the division of the cytoplasm (cytokinesis) in animal cells.

Components of the cytoskeleton found in all eukaryotic cells

• Actin filaments (also known as microfilaments)

• Intermediate filaments

• Microtubules

Actin filaments (microfilaments)

• Two-stranded helical chains of actin monomers.

• Arranged as linear bundles or networks, eg cell cortex beneath plasma membrane.

25 nm

Actin filaments (microfilaments)

­ Networks of actin filaments reinforce the cell surface.

­ Involved in restructuring the cell surface during cytokinesis.

­ Involved in muscle contraction.

Intermediate filaments

• Rope-like fibres that are composed of fibrous proteins from a large family.

• Involved in the maintenance of the shape of whole cells or parts of cells, including the nuclear envelope.

Microtubules

­ Largest element of the cytoskeleton.

­ Hollow cylinders composed of monomers of tubulin proteins.

25 nm

Microtubules are dynamic structures

Animation of microtubule polymerisation.

Microtubules radiate from a specific cellular location.

The microtubule-organising centre (MTOC).

Animal cells have a single well-defined MTOC: the centrosome.

Clips of stained microtubules showing dynamic behaviour and unstable microtubules.

Nucleated microtubules

A pair of centrioles help to organise and duplicate the centrosome

Microtubules

Microtubules form a network of intracellular ‘railway tracks’ along which transport of organelles occurs, eg vesicles and mitochondria.

Video clip of kinesin motor protein moving along microtubule.Movement of organelles along microtubles.

Rearrangement of cytoskeleton during cell division

Microtubules form spindle fibres

Spindle fibres attach to replicated chromosomes

Kinetochore microtubules

Spindle fibres form the mitotic spindle

Spindle fibre shortening separates the replicated chromosomes

Clips of chromosome separation: cultured lung cell and lily.

Role of spindle fibres in mitosis: animation.

Can you identify the elements of the cytoskeleton and their function in the Inner Life

of the Cell animation?