The carbohydrates are generally classified into three groups. They are: 1. Mono-Saccharides 2. Oligosaccharides (oligo = few) 3. Polysaccharides (poly = many).
Type # 1. Mono-Saccharides:
The mono-saccharides are known as simple sugars which possess free aldehyde ( CHO) or ketone (= CO) group and 2 or more hydroxyl (- OH) groups. Their general formula is Cn (H2O) or CnH2nOn.
The hexoses which include aldohexose D-glucose and the ketohexose D-fructose are the most common mono-saccharides in nature.
The aldopentoses D-ribose and 2-doxy D-ribose are components of nucleotides. A nucleotide in the nucleoside phosphosylated at one of its pentose hydroxyl groups.
The mono-saccharides are referred to as aldoses or ketoses on the basis of aldehyde and ketone group that they have. The examples of two families of monosaccharide’s are given in table 2.
Type # 2. Oligosaccharides (oligo = few):
These are the compound sugars which produce 2 to 10 molecules of the same or different mono-saccharides on hydrolysis
(i) Disaccharides – Sucrose, Lactose, maltose, Cellobiose, Trehalose, Gentiobiose, Melibiose
(ii) Trisaccharides – Rhamninose, Gentianose, Raffinose (= Melitose), Rabinose, Melezitose
(iii) Tetrasaccharides – Stachyose, Scorodose
(iv) Pentasaccharide – Verbascose
Type # 3. Polysaccharides (poly = many):
These are also compound sugars which bear more than 10 molecules of monosaccharides on hydrolysis. Their general formula is (C6H10O5). Some common examples are:
(i) Homopolysaccharides – Starch, Glycogen, Inulin, Cellulose, Pectin, Chitin
(ii) Heteropolysaccharides – Specific soluble sugars of pneumococcus type III, Hyaluronic acid, Chondrotin.