Defined in the broadest sense, glycobiology is the study of the structure, biosynthesis and biology of glycans. All cells and many proteins in nature are covered with a dense and complex array of covalently attached sugar chains (called oligosaccharides or glycans). The biological roles of these glycans become particularly important in constructing complex multicellular organs and organisms, a process which requires interactions of cells with one another, and with the surrounding extracellular matrix. Most classes of glycans are on the surface of cellular and secreted macromolecules. In addition, simple, rapidly turning-over protein-bound glycans are abundant in the nucleus and cytoplasm, where they serve as regulatory switches. During the initial phase of the modern revolution in molecular biology in the 1970s and 80s, studies of glycans lagged behind those of the other major classes of molecules. This was in large part due to the inherent structural complexity of glycans, the difficulty in easily determining their sequence, and the lack of in-depth information about the genetic control of their biosynthesis. The development of a variety of new technologies for exploring the structures of these chains and the cloning of most of the genes involved in synthesizing them has now opened up a new frontier of molecular and cellular biology called glycobiology (a term coined in 1988 by Rademacher, Parekh, and Dwek). Glycobiology is also an integrative science, crossing all subfields of chemistry, biology, and medicine.
A significant portion of the genome of most organisms is committed to the synthesis and recognition
of glycans. This, together with the increasing complexity and diversity of glycans during
evolution indicates that they have many biological roles yet to be discovered. The following summary indicates that we already know a lot about the biological
relevance of glycosylation.