Cytoskeleton & Extracellular Components The cytoskeleton is a network of fibers that extend through the cytoplasm in the cell. There are 3 basic structures of the cytoskeleton: Microtubules, Microfilaments, Intermediate Filaments. – They provide for the functions of support, motility, and regulation.

Microtubules Hollow tubes made of a & b tubulin (globular protein) – Main fx is in the maintenance of cell shape, cell motility, & organelle movement Thickest of the cytoskeleton elements – Centrosomes located near the nucleus in plants grow tubules outward resisting compression forces – Centrioles a set of 9 tubes set in a ring active in replication in animals

Microtubules – Flagella arrangement propel using a whip-like motion mostly single per motile cell but can be double (or few) as well the flagellum is anchored to the basal body (later becomes the centriole in a fertilized egg) the bending movement comes from dyneim, a larger protein-complex that attaches the tubules – Cilia much like flagella but work in a rowing motion together there are usually many per cell

Microfilaments 2 intertwined strands of actin Actin – a double twisted rod – can be branched forming a fibrous network – gives the cortex (outer cytoplasmic layer) its semisolid consistency to maintain shape Muscle motor unit – long actin filaments bridged with myosin, a protein that "walks" the fiber causing contraction

Microfilaments Pseudopodia (fake foot) – actin network that converts the solution into gel in ameoboid organisms Cytoplasmic streaming – a process in large plant cells where cytoplasm is directed to other parts of the cell to speed delivery of needed materials

Intermediate Filaments Fibrous keratin proteins supercoiled into thicker strands – Made of a family of keratin proteins – Permanent structures that persist long after the cell dies Skin, hair, nails Nuclear lamina – important in reinforcing the shape of the cell

Extracellular Components and Connections Between Cells Cell Walls (Plants) – protects – maintains shape – prevents excessive uptake of water – composed of microfibrils of cellulose embedded in a matrix of protein and polysaccharides – parts: primary cell wall - thin and flexible middle lamella - rich in pectins (polysaccharide) which glue cells together secondary cell - wall thick strong structure between the primary wall and the plasma membrane

Extracellular Components and Connections Between Cells Extracellular Matrix - ECM (animal cells) – consists mostly of glycoproteins (collagen) incorporated into the cell walls ~50% of the protein found in the human body – creates a fibrous network that embeds itself into protoglycans (another fibrous glycoprotein) – fibronectins are glycoproteins attached to integrins on the outer membrane that transmit changes in the outer environment into the cells Integrins transmit messages into the cytoplasm from the ECM

Extracellular Components and Connections Between Cells Intercellular junctions – plasmodesmata (plants) channels where cytosol communicates between cells – Tight junctions (continuous seal around cell preventing leakage), – Desmosomes (fasten cells together into strong sheets) – Gap junctions (cytoplasmic channels from one cell to another)