Chapter 14: Cell Walls, the Extracellular Matrix, and Cell Interactions
Chapter Summary
CELL WALLS
Bacterial Cell Walls: The principal component of bacterial cell walls is a peptidoglycan consisting of polysaccharide chains cross-linked by short peptides.
Eukaryotic Cell Walls: The cell walls of fungi, algae, and higher plants are composed of fibrous polysaccharides (e.g., cellulose) embedded in a gel-like matrix of polysaccharides and proteins. Their rigid cell walls allow plant cells to expand rapidly by the uptake of water.
THE EXTRACELLULAR MATRIX AND CELL-MATRIX INTERACTIONS
Matrix Structural Proteins: The major structural proteins of the extracellular matrix are members of the large collagen protein family. Collagens form the fibrils that characterize the extracellular matrix of connective tissues, as well as forming networks in basal laminae.
Matrix Polysaccharides: Polysaccharides in the form of glycosaminoglycans and proteoglycans make up the bulk of the extracellular matrix. They bind to and modify the collagen fibrils and interact with all other matrix molecules.
Matrix Adhesion Proteins: Matrix adhesion proteins link the components of the extracellular matrix to one another and are the major binding sites for integrins, which mediate most cell-matrix adhesions.
Cell-Matrix Interactions: Integrins are the major cell surface receptors that attach cells to the extracellular matrix. At focal adhesions and hemidesmosomes, integrins provide stable links between the extracellular matrix and the actin and intermediate filament cytoskeletons, respectively.
CELL-CELL INTERACTIONS
Adhesion Junctions: Selective cell-cell interactions are mediated by four major groups of cell adhesion proteins: selectins, integrins, immunoglobulin (Ig) superfamily members, and cadherins. The cadherins link the cytoskeletons of adjacent cells at stable cell-cell junctions.
Tight Junctions: Tight junctions prevent the free passage of molecules between epithelial cells and separate the apical and basolateral domains of epithelial cell plasma membranes.
Gap Junctions: Gap junctions are open channels connecting the cytosols of adjacent animal cells. Electrical synapses are gap junctions that mediate signaling between cells of the nervous system.
Plasmodesmata: Adjacent plant cells are linked by cytoplasmic connections called plasmodesmata.
