Lecture 4: The Cytoskeleton

The Cytoskeleton

• Network of fibers extending throughout the cytoplasm
• Plays a major role in organizing the structures and activities of the cell
- Pulls chromosomes during mitosis
- Splits the cell during cytokinesis
- Provides machinery for muscle contraction
- Provides machinery for axon and dendrite extension

Microfilaments

• ~ 7 nm in diameter
• Called actin filaments (built from Actin proteins)
• Ubiquitous to all living cells
• e.g. cortical microfilaments inside the plasma membrane that keep the cell's shape, part of the contractile apparatus of the muscle cell (actin-myosin complex)

Microtubules

• ~25 nm in diameter, 200 nm to 25 um in length
• Made from tubulin subunits
• Shape and support the cell
• e.g. microtubules separate chromosomes during cell division, cilia and flagella are made up of microtubules

Intermediate Filaments

• 8-12 nm in diameter • Each type is made from a different molecular subunit • More permanent fixtures that microfilaments or microtubules • e.g. intermediate filaments form the nuclear lamina of the nuclear envelope, intermediate filaments maintain and strengthen axons