The Cytoskeleton

● Network of Protein Filaments● Used in:

– Structural Support– Cell Movement– Movement of Vesicles within Cells

● Composed of three types of Cytoskeletal fibers– Actin Filaments– Microtubules– Intermediate Filaments

The Cytoskeleton

● Actin Filaments– Smallest of the fibers, 7nm in diameter– Two protein chains, loosely twined– Each subunit is the globular protein actin– Polarity designates direction of growth– Turn on polymerization when appropriate– Responsible for cellular movements

The CytoskeletonActin Filaments

The Cytoskeleton

● Microtubules– Ring-shaped tubes, 25nm in diameter– Consist of 13 protofilaments, arranged side by side

around a central core– Facilitate cellular movement and move materials

within the cell– Form nucleation centers near center of cell

● + end of microtubule radiates away from nucleation center

● - end of microtubule radiates towards nucleation center

The Cytoskeleton

Microtubules

The Cytoskeleton

● Intermediate Filaments– Most durable of filaments– Tough, fibrous protein molecules twined together in

overlapping arrangement– Stable– Constitute mixed group of cytoskeletal fibers

● Vimentin (most common)● Keratin (epithelial cells)

The CytoskeletonIntermediate Filaments

The Cytoskeleton

● Microtubule Organizing Centers– Centrioles– Centrosome– Pericentriolar Material

The Cytoskeleton

● Centrioles– Barrel-shaped organelles– Found in cells of animals and protists– Occur in pairs– Located in right angles to each other outside the

nuclear membranes

The Cytoskeleton

● Centrosome– Region surrounding centrioles– Responsible for reorganization of microtubules that

occurs during cell division– Centrosomes of plants and fungi lack centrioles

The Cytoskeleton

The Cytoskeleton

● Pericentriolar Material– Contains ring-shaped structures composed of

tubulin– Nucleates the assembly of microtubules in animal

cells– Called microtubule-organizing centers

The Cytoskeleton

Pericentriolar Material

The Cytoskeleton

● Movement of Materials within Cells– Use of Actin Filaments in cells allows for movement– Cytoskeleton provides scaffold that holds certain

enzymes and other macromolecules in defined areas of cytoplasm

– By moving and anchoring particular enzymes near one another, responsible for organizing cell's activities

The Cytoskeleton

● Molecular Motors– A vesicle or organelle needs to be transported– A motor protein that provies the energy-driven

motion– A connector molecule that connects the vesicle to

the motor molecule– Microtubules on which the vesicle will ride like a

train on a rail