Carbohydrates are polyhydroxy aldoses, ketoses and their condensation products. Aldoses bear terminal aldehyde or -CHO group while ketoses have an internal ketone or -CO- group. Carbohydrate is a hydrate of carbon or Cn(H20)n or (CH20)n having carbon, hydrogen and oxygen where hydrogen and oxygen occur in the ratio of 2:1 Carbohydrate are also called saccharides because their basic components are sugars. Carbohydrates are of two types-small and complex. Small carbohydrates are further differentiated into monosaccharides, derived rponosaccharides and oligosaccharides. Large carbohydrates are called polysaccharides.
1. Monosaccharides : They are those sugars or
simple carbohydrate monomers which cannot be hydrolysed further into smaller components. They have a general formula of CnH2nOn. Depending upon the number of carbon atoms, monosaccharides ! are of five types : !
(a) Trioses, (b) Tetroses, (c) Pentoses, (d) Hexoses, J
(e) Heptoses. |
2. Derived monosaccharides : Monosaccharides are j
modified variously to form a number of different I substances. The important derivatives are : \
(i) Deoxy Sugar: Deoxygenation of ribose produces :
(ii) Amino sugars, (iii) Sugar acid, (iv) Sugar alcohol, j
3. Oligosaccharides : They are small carbohydrates : which are formed by condensation of 2-9 monosaccharides. Therefore, oligosaccharides belong to the category of compound carbohydrates. Depending upon the number of monosaccharides, molecules condensed to form oligosaccharides, the j latter are known as disaccharide, trisaccharides, tetrasaccharides, pentasaccharides etc. Large oligosaccharides having branched or unbranched chains occur attached to cell membranes. Polysaccharides : They are complex carbohydrates which are formed by polysaccharides, also called glycans. They are long chained. The chains may be branched or unbranched.
Polysacharides are of two types : Homopolysaccharides and heteropolysacharides Homopolysaccharides consists of similar type of sugar units like starch while heteropolysacharides are made up of dissimilar sugar units e.g., chitin.