Composition And Metabolism Of Carbohydrates
Classify carbohydrates with suitable examples.
Answer.
Definition Of Carbohydrates
Carbohydrates may be defined as polyhydroxy aldehydes or ketones or compounds which produce them on hydrolysis
Classification Of Carbohydrates
Carbohydrates are classified into 3 groups:
- Monosaccharides
- Oligosaccharides
- Diasaccharides
- Polysaccharides
Monosaccharides
- Monosaccharides are the simplest group of carbohydrates and are referred to as simple sugars
- They cannot be further hydrolysed
- The monosaccharides are divided into different categories depending on the functional group and the number of carbon atoms
- When the functional group in monosaccharides is an aldehyde, they are known as aldoses e.g. glyceraldehyde, glucose
- When the functional group is a keto group, they are known as ketoses e.g. dihydroxyacetone, fructose
- Based on the number of carbon atoms, the monosaccharides are regarded as trioses (3C), tetroses (4C), pentoses (5C), hexoses (6C) and heptoses (7C).
Oligosaccharides
- Oligosaccharides contain 2 to 10 monosaccharide molecules which are liberated on hydrolysis
- Based on the number of monosaccharide units present the oligosaccharides are further subdivided as –
- Disaccharides (2) – e.g. Maltose
- Trisaccharides (3) – e.g. Raffinose
- Tetrasaccharides (4) – e.g. Stachyose
- Pentasaccharides (5) – e.g. Fondaparinux
Disaccharides
- Disaccharides are sugars which yield two molecules of the same or different molecules of monosaccharides on hydrolysis e.g. maltose, lactose and sucrose
- Maltose yields two molecules of glucose on hydrolysis
- Lactose yields one molecule of glucose and one molecule of galactose on hydrolysis
- Sucrose yields one molecule of glucose and one molecule of fructose on hydrolysis
Polysaccharides
- Polysaccharides are sugars which yield more than ten molecules of monosaccharides on hydrolysis
- They are of two types
- Homo-polysaccharides – they are polymers of the same monosaccharide units e.g. – starch, glycogen, inulin, dextrin, dextran and cellulose
- Hetero-polysaccharides – they are polymers of different monosaccharide units or their derivatives.
They are also known as mucopolysaccharides or glycosaminoglycans (GAGS) e.g. – keratan sulfate, chondroitin sulfate, heparin and hyaluronic acid.
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