Now that the human genome has been deciphered, much of the fanfare surrounding it has transferred to the proteome, the full complement of proteins made from the genetic "blueprints" stored in our cells. Proteins, after all, carry out most of the work in the body, and an understanding of how they behave, the press releases say, should translate into a font of ideas for curing all manner of ills. Yet living cells are more than genes and proteins. Two other major classes of molecules--carbohydrates (simple and complex sugars) and lipids (fats)--play profound roles in the body as well. These substances, too, need to be considered if scientists are to truly understand how the human machine operates and how to correct its maladies.

Sugars in particular perform an astonishing range of jobs. Once regarded mainly as energy-yielding molecules (glucose and glycogen) and as structural elements, they are now known to combine with proteins and fats on cell surfaces and, so situated, to influence cell-to-cell communication, the functioning of the immune system, the ability of various infectious agents to make us sick, and the progression of cancer. They also help to distinguish one cell from another and to direct the trafficking of mobile cells throughout the body, among other tasks. So ubiquitous are these molecules that cells appear to other cells and to the immune system as sugarcoated....

continued at Scientific American Digital