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Carbohydrates introduction

For various living organisms, 16 macronutrients and 11 micronutrients (total 27) are essential. In living organisms, H, 0, C of N are most abundant elements, constituting about 99% of mass, where C = 50%, o = 25-30 and N = 8-10%.

Carbohydrates are organic substances mainly consisting of C, H and 0; some carbohydrates also contain S, N and P. The word carbohydrates is derived from the French word ‘hydrate de carbon’, which means hydrate of carbon. Its general formula is CnH2On (n = generally 3-7) or Cx(H20)y, where H and 0 are in 2 : 1 ratio, as in H20. But, many substances are not carbohydrates, but have the similar general formula of carbohydrates,

e.g., (i) formaldehyde (ii) acetic acid
– (CH20) – (where, n = 1) – (CH3COOH) or (C2H40)- (where, n = 2)
H OH
| |
C = O C=O
| |
H H

Similarly, some carbohydrates do not fulfill the general formula of carbohydrates,
e.g., (i) deoxyribose – (C5H10O4) (ii) rhamnose – (C6H12O5)
H
|
C = O
|
H-C-H
|
H-C-OH
|
H-C-OH
|
CH20H

Thus, more precise definition of carbohydrates is that they are polyhydroxy aldoses or

ketoses or their condensation products (chains or rings of C with 2 or more -OH groups).

(i) aldoses                                                                   (ii) ketoses                                                (- CHO in terminal position)                                                  (>C=O in sub-terminal position)

H                                                                                   H

|                                                                                     |

C = O                                                                            C=O

|                                                                                    |

R                                                                                   R’

 

Depending upon the number of monomeric units, carbohydrates are of three types.