Glycolipids are phospholipids attached to oligosaccharides, and as noted, are part of the glycocalyx. Both are only found on the extracellular surface. Glycolipids are synthesized in much the same way as glycoproteins. Specific enzymes catalyze initial glycosylation of either phospholipids or polypeptides, followed by the addition of more sugars. Along with glycoproteins, glycolipids play roles in cell-cell recognition and the formation of tissues. The glycans on the surfaces of one cell will recognize and bind to carbohydrate receptors (lectins) on adjacent cells, leading to cell-cell attachment as well as intracellular responses in the interacting cells. Glycoproteins and glycolipids also mediate the interaction of cells with extracellular molecular signals and with chemicals of the extracellular matrix (ECM). The ECM includes components of connective tissue, basement membranes, in fact any surface to which cells attach.
292 The Extracellular Matrix