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.

Glycans (see Box S-1) are ubiquitous. All living cells are coated on their cell membranes with glycans or include glycan polymers as integral components of their cell walls. They play diverse roles, including critical functions in the areas of cell signaling, molecular recognition, immunity, and inflammation. They are the cell surface molecules that define the ABO blood groups, influencing an individual’s ability to receive another’s blood. Glycans are attached to specific locations on many proteins, modulating aspects of their biological activity through molecular recognition or affecting their circulation time in blood. The difference between glycan molecules added by humans when they naturally produce the protein erythropoietin, which affects red blood cell production, and glycan molecules present when this protein drug is produced commercially in cell culture, serves as the basis for antidoping tests in athletes. They are also central components of plant cell walls, which enable plants to grow upright and to resist degradation from the environment and from microbes.

Advances in the life sciences over the past several decades have led to a greater understanding of many of the basic mechanisms present in biological systems. Stimulated by the Human Genome Project, there have been improvements in understanding the central dogma of molecular biology. Sequences of DNA—genes—are transcribed into RNA, which in turn are translated to form proteins. This basic understanding, along with advances in the tools used to study biology, underpins the expansion of both genomics and proteomics. The wide array of posttranslational modifications that occur on proteins are also part of this increasingly clear picture. Protein glycosylation, one of the most common forms of post-

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