Carbohydrates

Carbohydrates are the most abundant natural organic compounds on Earth. The term "carbohydrate" derives from their general formula of Cn(H2O)n, first determined in the nineteenth century, and indicates that these compounds are hydrates of carbon. Carbohydrates are more specifically defined as polyhydroxy aldehydes or ketones and the products derived from them. Carbohydrates are synthesized via photosynthesis by plants, algae, and some bacteria. Animals feeding on these organisms then use the energy stored in these compounds.

Energy storage is not the only function of carbohydrates. They have a variety of functions in living organisms, including their contribution to the structure of cell walls and their vital role in communication at the site of cell membranes. Carbohydrates form part of the backbone of RNA and DNA molecules, and they are also found linked to proteins and lipids as glycoproteins and glycolipids. The three basic groups of carbohydrates based on size are: monosaccharides, oligosaccharides, and polysaccharides (saccharide from the Greek sakcharon, or "sugar"). The oligosaccharides and polysaccharides are composed of a few and many monosaccharides, respectively. Monosaccharides have two major groups: the aldoses and the ketoses.