The diversity of the thousands of proteins found in nature arises from the intrinsic properties of only 20 commonly occurring amino acids. These features include:
(i) The capacity to polymerize, (ii) novel acid–base properties, (iii) varied structure and chemical functionality in the amino acid side chains, and (iv) chirality
Amino acids are classified into different ways based on polarity, structure, nutritional requirement, metabolic fate. Generally used classification is based on polarity.
General Classification
| Trivial name | Symbols | Systematic name | Formula |
|---|---|---|---|
| Alanine | Ala A | 2-Aminopropanoic acid | CH3-CH(NH2)-COOH |
| Arginine | Arg R | 2-Amino-5-guanidinopentanoic acid | H2N-C(=NH)-NH-[CH2]3-CH(NH2)-COOH |
| Asparagine | Asn N | 2-Amino-3-carbamoylpropanoic acid | H2N-CO-CH2-CH(NH2)-COOH |
| Aspartic acid | Asp D | 2-Aminobutanedioic acid | HOOC-CH2-CH(NH2)-COOH |
| Cysteine | Cys C | 2-Amino-3-mercaptopropanoic acid | HS-CH2-CH(NH2)-COOH |
| Glutamine | Gln Q | 2-Amino-4-carbamoylbutanoic acid | H2N-CO-[CH2]2-CH(NH2)-COOH |
| Glutamic acid | Glu E | 2-Aminopentanedioic acid | HOOC-[CH2]2-CH(NH2)-COOH |
| Glycine | Gly G | Aminoethanoic acid | CH2(NH2)-COOH |
| Histidine | His H | 2-Amino-3-(1H-imidazol-4-yl)- propanoic acid | See structure in Histidine |
| Isoleucine | ILe I | 2-Amino-3-methylpentanoic acid | C2H5-CH(CH3)-CH(NH2)-COOH |
| Leucine | Leu L | 2-Amino-4-methylpentanoic acid | (CH3)2CH-CH2-CH(NH2)-COOH |
| Lysine | Lys K | 2,6-Diaminohexanoic acid | H2N-[CH2]4-CH(NH2)-COOH |
| Methionine | Met M | 2-Amino-4-(methylthio)butanoic acid | CH3-S-[CH2]2-CH(NH2)-COOH |
| Phenylalanine | Phe F | 2-Amino-3-phenylpropanoic acid | C6H5-CH2-CH(NH2)-COOH |
| Proline | Pro P | Pyrrolidine-2-carboxylic acid | See Structure in Proline |
| Serine | Ser S | 2-Amino-3-hydroxypropanoic acid | HO-CH2-CH(NH2)-COOH |
| Threonine | Thr T | 2-Amino-3-hydroxybutanoic acid | CH3-CH(OH)-CH(NH2)-COOH |
| Tryptophan | Trp W | 2-Amino-3-(lH-indol-3-yl)- propanoic acid | See Structure Tryptophan |
| Tyrosine | Tyr Y | 2-Amino-3-(4-hydroxyphenyl)- propanoic acid | See Structure Tyrosine |
| Valine | Val V | 2-Amino-3-methylbutanoic acid | (CH3)2CH-CH(NH2)-COOH |
| Unspecified amino acid | Xaa X | ||
