The cytoskeleton

What is the cytoskeleton

"The bones and muscles" of the cell

What are the 3 filamentous networks unique to eukaryotic cells

1. microtubules

a. made of tubulins

b. hollow tubes (25 nm diameter)

2. microfilaments

a. made of actin

b. filaments (7 nm across)

3. intermediate filaments

a. made of intermediate filament proteins cables (10 nm across)

What is the organization of microtubules in a typical eukaryotic cell

Microtubules have polarity (- and + ends)

Grow out from a "microtubule-organizing center" (MTOC)

Example: the centrosome

Consider a nerve cell (e.g., motor neuron)

Cell body in the spinal cord; axon extends to the muscle in the leg

Biosynthetic machinery (genes, mRNA, ribosomes in the cell body).

Vesicles with neurotransmitters and other material needed at the synapse

Microtubules are used like "railroad" tracks to transport vesicles and other

"cargo"

Microtubules and axonal transport

"motor proteins" bind to both vesicles and microtubules

Use the energy of ATP hydrolysis to "walk" up or down microtubules

anterograde motor= kinesin

Retrograde motor = cytoplasmic dynein

Microtubules and cell movement

Cellular movement mediated by cilia and flagellae

Sperm (flagellum)

Paramecium (cilia)

Cilia and flagellae contain highly organized microtubules

Sliding of microtubules causes movement

Anoneme Microtubules

"9+2" arrangement of microtubules

Dynein motor protein interacts with microtubules

Mediates the sliding of microtubules, causing wavelike motion

Cytoskeletal networks are dynamic structures

MT and MF networks are dramatically reorganized in diving cells

MTs form the mitotic spindle: pulls chromosomes apart

MFs form a contractile ring: split cells in two