Amino Acid – Classification, Properties, Essential and Function


Amino Acid – Classification, Properties, Essential and Function

Definition of Amino Acid:
Amino acids are organic acids which contain both basic (amino – NH2) and acidic (carboxyl COON) groups and have general formula


Classification of Amino Acid:

Based on Composition they are Classified as:

1) Aliphatic mono amino monocarboxylic acids: e.g. glycine, alanine, valine, leucine, isolucine
2) Aromatic amino acids: e.g. phenylalanine, tyrosine and tryptophan
3) Hydroxy amino acids: e.g. serine, threonine
4) Acidic or dicarboxylic acids: e.g. Aspartic acid and glutamic acids
5) Basic amino acids: e.g. Lysine, arginine and histidine.
6) Sulphur containing amino acids: e.g. methionine, cysteine
7) Secondary amino acids: e.g. proline and hydroxyproline
8) Non protein amino acid: e.g. Aminobutyrate, homoserine and cystathionine in plants.

Properties of Amino Acids:

Colour less, crystalline, tufts of slender needles (Tyrosine) to hexagonal plates (cystine). Taste varies from sugar sweet (glycine, alanine) through tasteless (Tyrosine) to bitter (arginine).
All amino acids except glycine contain at least one asymmetric carbon atom ornithine needles (tyrosine) to hexagon plates (cysteine)

1) Solubility
2) Amphoteric Nature
3) Esterification
4) Ninhydrin Reaction
5) Reaction of alpha amino acid with HCL
6) Reaction of carboxylic group with NaOH
7) Zwitter ion
8) Electrical Property

Amino group of one amino acid combine with carboxyl group of second amino acid linkage called peptide.  Explain the term dipeptide, Tri peptide, Tetra peptide and polypeptide.

Buret Reaction:

Peptide containing two or more peptide bonds will react with Cu2+ in an alkaline solution to form violet blue colour

Essential Amino Acids:

Most of the naturally occurring amino acids are indispensable. Naturally occurring ten amino acids cannot be synthesized in animal body for which external supplementation is needed Ex. Tryptophan, Histidine, Arginine, Leucine, Isoleucine, Lysine, Valine, methionine, phenylalanine, Threonine.

Functions of Amino Acids:

i) Formation of Proteins
ii) Maintenance of Tissues
iii) Formation of Enzymes, Hormones and Antibodies.

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