Amino Acid Chart & Code Table — 20 Amino Acids
There are 20 standard amino acids encoded by the genetic code, each with a one-letter amino acid code and a three-letter abbreviation. This amino acid table lists every residue with its side-chain class, whether it is essential in the human diet, its average residue mass, Kyte–Doolittle hydropathy and the codons that encode it.
Amino acid code quick lookup
Use this compact amino acid code table to look up a one-letter code, three-letter abbreviation or full amino acid name.
| Amino acid | 3-letter | 1-letter | Class | Essential | Mass (Da) | Hydropathy | Codons |
|---|---|---|---|---|---|---|---|
| Alanine | Ala | A | Nonpolar | No | 71.1 | +1.8 | GCT, GCC, GCA, GCG |
| Arginine | Arg | R | Basic | No | 156.2 | -4.5 | CGT, CGC, CGA, CGG, AGA, AGG |
| Asparagine | Asn | N | Polar | No | 114.1 | -3.5 | AAT, AAC |
| Aspartic acid | Asp | D | Acidic | No | 115.1 | -3.5 | GAT, GAC |
| Cysteine | Cys | C | Polar | No | 103.1 | +2.5 | TGT, TGC |
| Glutamic acid | Glu | E | Acidic | No | 129.1 | -3.5 | GAA, GAG |
| Glutamine | Gln | Q | Polar | No | 128.1 | -3.5 | CAA, CAG |
| Glycine | Gly | G | Nonpolar | No | 57.1 | -0.4 | GGT, GGC, GGA, GGG |
| Histidine | His | H | Basic | Yes | 137.1 | -3.2 | CAT, CAC |
| Isoleucine | Ile | I | Nonpolar | Yes | 113.2 | +4.5 | ATT, ATC, ATA |
| Leucine | Leu | L | Nonpolar | Yes | 113.2 | +3.8 | TTA, TTG, CTT, CTC, CTA, CTG |
| Lysine | Lys | K | Basic | Yes | 128.2 | -3.9 | AAA, AAG |
| Methionine | Met | M | Nonpolar | Yes | 131.2 | +1.9 | ATG |
| Phenylalanine | Phe | F | Nonpolar | Yes | 147.2 | +2.8 | TTT, TTC |
| Proline | Pro | P | Nonpolar | No | 97.1 | -1.6 | CCT, CCC, CCA, CCG |
| Serine | Ser | S | Polar | No | 87.1 | -0.8 | TCT, TCC, TCA, TCG, AGT, AGC |
| Threonine | Thr | T | Polar | Yes | 101.1 | -0.7 | ACT, ACC, ACA, ACG |
| Tryptophan | Trp | W | Nonpolar | Yes | 186.2 | -0.9 | TGG |
| Tyrosine | Tyr | Y | Polar | No | 163.2 | -1.3 | TAT, TAC |
| Valine | Val | V | Nonpolar | Yes | 99.1 | +4.2 | GTT, GTC, GTA, GTG |
NonpolarPolarAcidicBasic· Mass = average residue mass · Hydropathy = Kyte–Doolittle
Essential vs non-essential amino acids
Nine of the twenty amino acids are essential: the human body cannot synthesise them, so they must come from the diet — histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. The remaining eleven are non-essential (or conditionally essential) and can be made from other metabolites.
Side-chain classes
Amino acids are grouped by the chemistry of their side chain. Nonpolarside chains are hydrophobic and tend to pack into a protein's core. Polar side chains are uncharged but hydrophilic. Acidic (Asp, Glu) carry a negative charge at neutral pH and basic(Lys, Arg, His) carry a positive charge — together they determine a protein's isoelectric point and net charge.
Frequently asked questions
How many amino acids are there?
There are 20 standard (proteinogenic) amino acids encoded directly by the genetic code. Two more — selenocysteine and pyrrolysine — are incorporated by special mechanisms in some organisms.
What are the essential amino acids?
The nine amino acids the human body cannot make and must get from food are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.
What is the difference between the one-letter and three-letter codes?
Both name the same amino acid. Three-letter codes (e.g. Ala, Gly) are easier to read; one-letter codes (e.g. A, G) are compact and used in sequence files and most software, including SeqBench.
What are the one-letter codes for amino acids?
The standard one-letter amino acid codes are A Ala, R Arg, N Asn, D Asp, C Cys, Q Gln, E Glu, G Gly, H His, I Ile, L Leu, K Lys, M Met, F Phe, P Pro, S Ser, T Thr, W Trp, Y Tyr and V Val.
What amino acids do Q, E, N and K stand for?
Q is glutamine, E is glutamate (glutamic acid), N is asparagine and K is lysine. These single-letter codes are used in protein sequences and amino acid tables.
What do nonpolar, polar, acidic and basic mean?
They classify the amino acid's side chain. Nonpolar side chains are hydrophobic; polar ones are uncharged but hydrophilic; acidic side chains carry a negative charge at neutral pH; basic ones carry a positive charge.
What is hydropathy?
Hydropathy (here the Kyte–Doolittle scale) measures how hydrophobic an amino acid is. Positive values are hydrophobic (water-avoiding), negative values hydrophilic. Averaged over a protein it gives the GRAVY score.
See also
Related tools and references
Use these related pages when this table raises a practical calculation or workflow question.
Tools
Translate a nucleotide sequence to protein in any or all six reading frames.
Optimise a protein or CDS for expression in E. coli, human, yeast, CHO, Pichia and more.
Compute molecular weight, isoelectric point, extinction coefficient and composition.
Guides
Nearby reference tables
Standard genetic code table for translating DNA or RNA codons.
Per-codon usage frequencies for E. coli, human, yeast, CHO, Pichia, insect, Arabidopsis and zebrafish.
Alternative translation tables and codon reassignments beyond the standard code.