Carbohydrates are indispensable to life on Earth. In their simplest form, they serve as a primary energy source for sustaining life. For the most part, however, carbohydrates appear not as simple sugars but as complex molecular conjugates known as polysaccharides or glycans.

Polysaccharides come in many forms and sizes, from linear chains (polysaccharides) to strongly branched complexes bristling with antennae-like extensions. And although proteins and nucleic acids like DNA have traditionally induced far more scientific attention, polysaccharides are also key to life. They are ubiquitous in nature, creating the complex sugar coat that surrounds the cells of almost every organism and filling the spaces between these cells.

As part of this so-called extracellular matrix, polysaccharides, with their diverse chemical structures, play a vital role in transmitting important inter and extra cellular biochemical messages. In this way, these sugars guide the cellular communication that is vital for healthy cell and tissue development and physiological function.

The Sweet Science of Glycobiology

Complex carbohydrates, molecules that are specially important for communication between cells, are coming under systematic study. Ram Sasisekharan and James R. Myette See: Glycobiology.

The central paradigm of actual molecular biology is that biological messages travels from DNA to RNA to protein. The power of this concept lies not only in its template-driven precision, but also in the ability to control any one class of molecules based on knowledge of another. With the upcoming deciphering of the genomic sequences of humans and various other usually studied model beings, even more spectacular advancements in the understanding of organical systems are expected.

In actual fact, creating a cell needs two other major types of molecules: lipids and carbohydrates. These molecules can serve as intermediates in producing energy, as signaling elements, or as structural components.

The structural roles of carbohydrates are specially important in the construction of complex multicellular organs and organisms, which require interactions of cells with one another and with the surrounding matrix. Indeed, all cells and various macromolecules in nature carry a dense and complex array of covalently linked sugar chains . In some instances, these polysaccharides can also be free-standing entities.

Since most polysaccharides are on the external surface of cellular and secreted macromolecules, they are in a position to control or mediate a wide variety of actions in cell-cell and cell-matrix interactions vital to the growth and function of all complex multicellular beings and also interactions between beings (e.g., between host and parasite). Also, simple, strongly dynamic protein-bound glycans are abundant in the nucleus and cytoplasm, where they appear to serve as controller switches.