Q.What are carbohydrates? How are they classified? [2 + 3]
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Start your 14-day free trial to unlock the full solution →Carbohydrates are polyhydroxy aldehydes/ketones (or their hydrolysis-yielding derivatives), classified into monosaccharides, oligosaccharides and polysaccharides.
Definition:
Carbohydrates are optically active polyhydroxy aldehydes or polyhydroxy ketones, or substances which on hydrolysis yield such units. Most of them have the empirical formula Cx(H2O)y, which made them look like 'hydrates of carbon' (hence the name). Chemically they are also called saccharides (Latin: saccharum = sugar).
Classification (on the basis of hydrolysis / number of sugar units produced):
- Monosaccharides:
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The simplest carbohydrates; they cannot be hydrolysed further into smaller sugar units.
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Further named by the number of carbon atoms and the carbonyl group: trioses, tetroses, pentoses, hexoses, etc.; and as aldoses (contain -CHO) or ketoses (contain >C=O).
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Examples: glucose and galactose (aldohexoses), fructose (a ketohexose), ribose (a pentose).
- Oligosaccharides:
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On hydrolysis give a small number (2 to about 10) of monosaccharide units.
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The commonest are disaccharides, giving two monosaccharide units on hydrolysis.
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Examples: sucrose (glucose + fructose), maltose (glucose + glucose), lactose (glucose + galactose). Trisaccharides such as raffinose also belong here.
- Polysaccharides:
- On hydrolysis give a large number of monosaccharide units.
- They are generally tasteless (non-sugars) and act as storage or structural materials. …
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