The Cytoskeleton

Objectives 1. Define cytoskeleton. 2. Explain the general functions of the cytoskeleton. 3. List the 3 types of cytoskeletal elements and their respective functions. 4. Describe the structure and function of the centrosome. 5. Describe the structure and functions of centrioles 6. List and describe the similarities and differences between cilia and flagella.

The Cytoskeleton Prior to 1970’s cytosol thought to be unorganized mix of organic molecules. Electron microscopy reveals organized cytosol Immunoflourescence microscopy identified protein fibers.

The Cytoskeleton Characteristics  Found in eukaryotes  Network of connected filaments and tubules  Extends from nucleus to plasma membrane  Elements can disassemble and reassemble

The Cytoskeleton Function  Maintains cell shape  Allows organelles to move

The Cytoskeleton Composed of 3 Types of Filaments Actin Intermediate Microtubules

Actin Filaments Characteristics Long, thin about 7 micrometers in diameter Occur in bundles or meshlike networks. Consist of two chains of globular actin monomers twisted to form a helix.

Actin Filaments Functions  Structural Form dense complex web just under the plasma membrane. In microvilli of intestinal cells likely shorten or extend cell into intestine. In plant cells, they form tracks along with chloroplasts circulate.

Actin Filaments Functions  Movement Iinteracts with motor molecule myosin Similar action accounts for pinching off cells during division and for amoeboid movement.

Intermediate Filaments Characteristics  8-11nm in diameter  8-11nm in diameter  Rope-like  Rope-like  Fibrous polypeptides  Fibrous polypeptides

Intermediate Filaments Functions  Support  Support Nuclear envelope Plasma membrane  Form cell-to-cell junctions.  Form cell-to-cell junctions.

MicrotubulesDescription  Ropelike, hollow cylinders (25nm in diameter, 0.2 micrometers in length).  Ropelike, hollow cylinders (25nm in diameter, 0.2 micrometers in length).  Composed of protein (Tubulin); alpha and beta  Composed of protein (Tubulin); alpha and beta  Associated with motor molecules (kinesins) kinesin and dynein

MicrotubulesFunctions  Maintain shape of cells  Tracks for vesicle and organelle movement  Different kinesins move different vesicles or organelles.

Centrioles Short cylinders with a 9+0 pattern of microtubules triplets. Short cylinders with a 9+0 pattern of microtubules triplets. Animals cells and most protista, two centrioles lying at right angles Animals cells and most protista, two centrioles lying at right angles Plant and fungal cells have equivalent of a centrosome but does not contain centrioles. Plant and fungal cells have equivalent of a centrosome but does not contain centrioles. Centrioles serve as basal bodies for cilia and flagella. Centrioles serve as basal bodies for cilia and flagella.

Centrioles Serve as basal bodies for cilia and flagella. Serve as basal bodies for cilia and flagella.

Cilia and Flagella Flagella (L. flagello, whip)  Cilia (L. cilium, eyelash, hair) Short, usually numerous hair like projections that can move in an undulating fashion.

Flagella longer than cilia, usually fewer Flagella are whip-like projections Flagella move whip-like (e.g. Sperm cells), cilia move swimmer-like/oar-like Differences

Construction Membrane-bounded cylinders (9+2 pattern of micortubules). Basal bodies Movement Microtubules slide past one another. Similarities

Growth By addition of tubulin to tips Movement Mechanism Microtubules slide past one another. Similarities (Cont’d)

Review 1. Define cytoskeleton. 2. Explain the general functions of the cytoskeleton. 3. List the 3 types of cytoskeletal elements and their respective functions. 4. Describe the structure and function of the centrosome. 5. Describe the structure and functions of centrioles 6. List and describe the similarities and differences between cilia and flagella.