BOX 1-1
Carbohydrate, Glycan, Saccharide, or Sugar?

Carbohydrate: A generic term used interchangeably in this report with sugar, saccharide, or glycan. This term includes monosaccharides, oligosaccharides, and polysaccharides as well as derivatives of these compounds.

Glycan: A generic term for any sugar or assembly of sugars, in free form or attached to another molecule.

Saccharide: A generic term for any carbohydrate or assembly of carbohydrates, in free form or attached to another molecule.

Sugar: A generic term often used to refer to any carbohydrate, but most frequently to low molecular weight carbohydrates that are sweet in taste.

sudden death due to inadequate energy. Diabetics must measure their blood sugar frequently to ensure proper glucose levels. Such measurements account for a significant number of the total number of diagnostic tests conducted each year in developed countries.

But glucose is not the only sugar molecule of importance to human health. Our cells carry complex sugars that comprise individual sugar molecules linked to one another in a multitude of ways. These complex sugars are usually referred to as glycans. Glycans are one of the four major classes of macromolecules—nucleic acids, proteins, and lipids being the other three—that are essential for life and are involved in every aspect of biology, medicine, and a number of practical applications. These other three classes often incorporate or rely on glycans for their activity—nucleic acids contain the carbohydrates ribose or deoxyribose, whereas proteins and lipids often require appended glycans for activity (glycoproteins and glycolipids, respectively). These structures, and combinations of these structures, contain information that is used for a wide variety of biological processes. Key facts about glycans and glycoscience are given in Box 1-2.

For example, one result of 3 billion years of evolution is that every cell of every organism is coated with a layer of glycans—the glycocalyx in animals or the cell wall in prokaryotes, plants, and fungi (see examples in Figure 1-1). The glycocalyx/cell wall contains high information content. On red blood cells the different sugars of the glycocalyx are responsible for the different blood groups—A, B, AB, and O (see Box 1-3). On cells of organs, these and other aspects of the glycocalyx can determine whether a



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