ABSTRACT
The surface layer of the cell membrane plays important roles in interactions between the cells and their surroundings, e.g., other cells, soluble biological molecules, and extracelluar matrices (Figure 17.1). Cellular recognition is usually initiated by direct contact with biologically functional molecules at the cell surfaces. The mechanical stress stimulates cell activation in some circumstances. Specific
interactions between receptors and ligands are important for cellular recognition. In many cases, multivalent binding (multivalency) can strengthen the ligand-receptor adhesion. In intercellular communication, accessory receptors are often required to stabilize the interaction by increasing the overall strength of the cell-cell adhesion, and co-receptors help activate cells by generating their own intracellular signals. Different combinations of receptors are likely to form complexes that transmit signals across membranes.
