A world of sugars
A world of sugar
Carbohydrates are among the most abundant organic compounds on earth.
The basic unit is a monosaccharide, such as glucose or galactose. Carbohydrates are classified according to their level of polymerization, leading to the formation oligosaccharides (from 2 to 12 units, for example saccharose or lactose) or polysaccharides (more than 12 units, up to several thousand, for example glycogen, starch or chitin).
The different carbohydrates can be digested by specific enzymes, leading to monosaccharides, a main source of energy for the cell. Oligo- and polysaccharides can also acquire a structural function, as in vegetal cellular wall (D-glucose polymers: cellulose) or in exoskeletons of insects and arthropods (N-Acetyl-Glucosamine polymers: chitin).
Moreover, carbohydrates have fundamental roles through the glycosylation process, which consists of a covalent binding of a more or less complex glycans onto proteins or lipids. A wide majority of normal (fecundation, ontogenesis...) or pathologic phenomena (oncogenesis, immune diseases...) that involve specific interaction between cells, proteins or antigens, are directed by glycans structures.