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 synthesize 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
Sources
- 1Nomenclature and Symbolism for Amino Acids and Peptides (Recommendations 1983), section 3AA-21.2 'The Code Symbols'IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN) · Eur J Biochem 138:9-37 (1984); also Biochem J 219:345-373 and Pure Appl Chem 56:595-624 · 1983/1984The 'Amino acid', '3-letter' and '1-letter' columns of the main table; the whole 'Amino acid code quick lookup' grid; and the FAQ answers 'What is the difference between the one-letter and three-letter codes?', 'What are the one-letter codes for amino acids?' and 'What amino acids do Q, E, N and K stand for?'.
- 2Expasy FindMod — amino acid residue masses (average and monoisotopic)SIB Swiss Institute of BioinformaticsThe 'Mass (Da)' column for all 20 rows, and the footnote 'Mass = average residue mass' (RESIDUE_MASS in src/lib/bio/protein.ts).
- 3A simple method for displaying the hydropathic character of a proteinKyte J, Doolittle RF · J Mol Biol 157(1):105-132 · 1982The 'Hydropathy' column for all 20 rows and the footnote 'Hydropathy = Kyte–Doolittle' (HYDROPATHY in src/lib/bio/protein.ts), plus the header sentence 'Kyte–Doolittle hydropathy' and the FAQ 'What is hydropathy?' including the GRAVY definition.
- 4Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids, Chapter 10 (Protein and Amino Acids)Institute of Medicine, Food and Nutrition Board, Panel on Macronutrients · The National Academies Press · 2005The 'Essential' Yes/No column (the nine-member ESSENTIAL set: H, I, L, K, M, F, T, W, V), the 'Essential vs non-essential amino acids' section, and the FAQ 'What are the essential amino acids?'.
- 5The Genetic Codes (NCBI Taxonomy) — transl_table 1, The Standard CodeElzanowski A, Ostell J · NCBI, National Library of Medicine · Last update of the Genetic Codes: 23 September 2024 (accessed 13 September 2026)The 'Codons' column for all 20 rows — the same STANDARD_CODON_TABLE the /codon-table page renders — and the header phrase 'the codons that encode it'.
Related tools and references
Tools
Translate a nucleotide sequence to protein in all six reading frames at once.
Optimize a protein or CDS for expression in E. coli, human, yeast, CHO, Pichia and more.
Compute molecular weight, isoelectric point, extinction coefficient and composition.
Nearby reference tables
Side-chain and terminal pKa values and how they set the isoelectric point.
Common affinity, epitope and solubility protein tags with amino acid sequences, mass, purification/detection and protease cleavage.
Standard genetic code table for translating DNA or RNA codons.