CBSE Class 12 Chemistry Notes: Biomolecules – Essential and Non – Essential Amino acids

(a)  These must be supplied to our diet as are not synthesized in body.

(b)  Some of them are

(1)  Valine   (2) Leucine  (3) Isoelucine (4) Phenylalanine  (5) Arganine (5) Threonine

(6) Tryptophan  (7) Methionine (8) Lysine (9) Arginine (10) Histadine

Note: Histidine and arginine are essential i.e. can be syntrhesized but not in quantities sufficient to permit normal growth.

Non – Essential Amino acids

These amino acids are synthesized in body.

Some of them are

These are as follows:

(1)  Glycine  (2) Alanine  (3) Tyrosine  (4) Serine (5) Cystine  (6) Proline (7) Hydroxyprocine

(8) Cysteine (9) Aspartic acid (10) Glutonic acid

Synthesis of a – amino acids

Protein can be hydrolyzed by refluxing with dilute hydrochloric acid to give a mixture of α – amino acids. The resulting mixture can be separated by

(a)  fractional crystallization.

(b)  Fractional distillation of their ester followed by hydrolysis (Fischer’s method)

(c)  Selective precipitation as salt with phosphotungstic and picric acid.

(d)  Distribution of amino acid between n – butanol saturated with water (Dakin’s method).

(e)  Column, paper and gas chromatography.

(f)   Electrophoresis.

By amination of α – halo acid

(i)

(ii)

By Gabriel synthesis 

By Strecker Synthesis 

(i)

(ii)

Note: Generally the aldehyde is treated with a mixture of ammonium chloride and potassium cyanide in aqueous solution.

Illustration 1

(A)

(B)

(C)

(D) All are correct

Solution: C

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