Amino acids are the basic structural units of proteins. An alpha-amino acid consists of an amino group, a carboxyl group, a hydrogen atom, and a distinctive R group bonded to a carbon atom, which is called the alpha-carbon because it is adjacent to the carboxyl (acidic) group. An R group is referred to as a side chain.(Stryer,1988)Amino Acids are commonly classified into the following groups based on the chemical and/or structural properties of their side chains :
- Aliphatic Amino Acids
- A Cyclic Amino Acid
- AAs with Hydroxyl or Sulfur-containing side chains
- Aromatic Amino Acids
- Basic Amino Acids
- Acidic Amino Acids and their Amides
| Rasmol Image | Amino Acid | 3-letter code | 1-letter code | Properties | Structure (un-ionised form) |
|---|---|---|---|---|---|
| Alanine | Ala | A | aliphatic hydrophobic neutral |  |
| Arginine | Arg | R | polar hydrophilic charged (+) |  |
| Asparagine | Asn | N | polar hydrophilic neutral |  |
| Aspartate | Asp | D | polar hydrophilic charged (-) |  |
| Cysteine | Cys | C | polar hydrophobic neutral |  |
| Glutamine | Gln | Q | polar hydrophilic neutral |  |
| Glutamate | Glu | E | polar hydrophilic charged (-) |  |
| Glycine | Gly | G | aliphatic neutral |  |
| Histidine | His | H | aromatic polar hydrophilic charged (+) |  |
| Isoleucine | Ile | I | aliphatic hydrophobic neutral |  |
| Leucine | Leu | L | aliphatic hydrophobic neutral |  |
| Lysine | Lys | K | polar hydrophilic charged (+) |  |
| Methionine | Met | M | hydrophobic neutral |  |
| Phenylalanine | Phe | F | aromatic hydrophobic neutral |  |
| Proline | Pro | P | hydrophobic neutral |  |
| Serine | Ser | S | polar hydrophilic neutral |  |
| Threonine | Thr | T | polar hydrophilic neutral |  |
| Tryptophan | Trp | W | aromatic hydrophobic neutral |  |
| Tyrosine | Tyr | Y | aromatic polar hydrophobic |  |
| Valine | Val | V | aliphatic hydrophobic neutral |  |