Amino Acid Chart
The Amino Acid Chart is a science reference tool covering amino acid chart, amino acid structure chart, essential amino acids chart, and the 20 amino acids chart. Use the chart below to look up values instantly. Printable and downloadable versions are available on this page.
Amino Acid Chart — All 20 Standard Amino Acids
| Amino Acid Name | 3-Letter Code | 1-Letter Code | Chemical Category | Side Chain Property | Molecular Weight | Essential or Non-Essential |
|---|---|---|---|---|---|---|
| Alanine | Ala | A | Aliphatic nonpolar | Small hydrophobic side chain | 89.1 Da | Non-essential |
| Arginine | Arg | R | Basic polar | Positively charged at physiological pH | 174.2 Da | Conditionally essential |
| Asparagine | Asn | N | Polar uncharged | Amide side chain | 132.1 Da | Non-essential |
| Aspartate | Asp | D | Acidic polar | Negatively charged at physiological pH | 133.1 Da | Non-essential |
| Cysteine | Cys | C | Polar uncharged | Contains sulphur — forms disulphide bonds | 121.2 Da | Conditionally essential |
| Glutamate | Glu | E | Acidic polar | Negatively charged at physiological pH | 147.1 Da | Non-essential |
| Glutamine | Gln | Q | Polar uncharged | Amide side chain — most abundant in blood | 146.2 Da | Conditionally essential |
| Glycine | Gly | G | Aliphatic nonpolar | Smallest amino acid — no side chain chirality | 75.0 Da | Non-essential |
| Histidine | His | H | Basic polar | Imidazole side chain — buffers near physiological pH | 155.2 Da | Essential |
| Isoleucine | Ile | I | Aliphatic nonpolar | Branched chain — hydrophobic | 131.2 Da | Essential |
| Leucine | Leu | L | Aliphatic nonpolar | Branched chain — most common in proteins | 131.2 Da | Essential |
| Lysine | Lys | K | Basic polar | Positively charged — modified by acetylation or ubiquitination | 146.2 Da | Essential |
| Methionine | Met | M | Aliphatic nonpolar | Contains sulphur — universal start codon amino acid | 149.2 Da | Essential |
| Phenylalanine | Phe | F | Aromatic nonpolar | Large hydrophobic benzyl side chain | 165.2 Da | Essential |
| Proline | Pro | P | Aliphatic nonpolar | Cyclic side chain — disrupts alpha helices | 115.1 Da | Non-essential |
| Serine | Ser | S | Polar uncharged | Hydroxyl group — phosphorylation site | 105.1 Da | Non-essential |
| Threonine | Thr | T | Polar uncharged | Hydroxyl group — phosphorylation site | 119.1 Da | Essential |
| Tryptophan | Trp | W | Aromatic nonpolar | Largest amino acid — indole side chain | 204.2 Da | Essential |
| Tyrosine | Tyr | Y | Aromatic polar | Hydroxyl on benzene ring — phosphorylation and signalling | 181.2 Da | Conditionally essential |
| Valine | Val | V | Aliphatic nonpolar | Branched chain hydrophobic | 117.1 Da | Essential |
Source: NCBI — Biochemistry (Berg et al.) and IUPAC amino acid nomenclature
Essential Amino Acids Chart
Essential amino acids cannot be synthesised by the human body in adequate amounts and must be obtained from dietary protein.
| Classification | Amino Acids | Key Dietary Sources |
|---|---|---|
| Essential (9) Must come from diet | Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine | Animal proteins (meat, eggs, dairy), soy protein. All 9 are found in complete proteins. |
| Conditionally Essential Required in higher amounts under stress, illness, or growth | Arginine, Cysteine, Glutamine, Tyrosine (and sometimes Glycine, Proline, Serine) | Illness, surgery, rapid growth, and extreme exercise increase requirements beyond what the body can synthesise. |
| Non-essential (11) Synthesised by the body | Alanine, Asparagine, Aspartate, Glutamate, Glycine, Proline, Serine (and others) | The body produces these from other compounds. Dietary intake still contributes. |
Source: WHO Protein and Amino Acid Requirements and Institute of Medicine — Dietary Reference Intakes
Amino Acid Structure Categories
| Category | Amino Acids in This Category | Side Chain Property | Biological Significance |
|---|---|---|---|
| Nonpolar aliphatic | Glycine, Alanine, Valine, Leucine, Isoleucine, Proline, Methionine | Hydrophobic — repel water | Tend to cluster in the interior of folded proteins away from aqueous environments. |
| Aromatic | Phenylalanine, Tyrosine, Tryptophan | Hydrophobic to amphipathic — absorb UV light at 280 nm | Protein UV absorbance at 280 nm used to quantify protein concentration in laboratory settings. |
| Polar uncharged | Serine, Threonine, Asparagine, Glutamine, Cysteine, Tyrosine | Hydrophilic — hydrogen bond donors and acceptors | Common sites for post-translational modifications including phosphorylation and glycosylation. |
| Positively charged (basic) | Lysine, Arginine, Histidine | Carry positive charge at physiological pH — bind DNA | Found abundantly in histone proteins that package DNA in the nucleus. |
| Negatively charged (acidic) | Aspartate, Glutamate | Carry negative charge at physiological pH — repel other negatively charged molecules | Active sites of many enzymes. Glutamate is the primary excitatory neurotransmitter in the brain. |
Source: NCBI — Biochemistry (Berg et al.)
Amino Acid Single-Letter Code Quick Reference
The single-letter amino acid code is used in protein sequence databases, alignments, and bioinformatics tools — it is worth memorising the most common ones.
| Letter Code | Amino Acid Name | Letter Code | Amino Acid Name |
|---|---|---|---|
| A | Alanine | L | Leucine |
| C | Cysteine | M | Methionine |
| D | Aspartate | N | Asparagine |
| E | Glutamate | P | Proline |
| F | Phenylalanine | Q | Glutamine |
| G | Glycine | R | Arginine |
| H | Histidine | S | Serine |
| I | Isoleucine | T | Threonine |
| K | Lysine | V | Valine |
| W | Tryptophan | ||
| Y | Tyrosine |
Amino Acid Reference Tool
Search, filter, and explore all 20 amino acids by name, abbreviation, essential status, polarity, or charge. Click any row to expand its codon list.
| Amino Acid | 3-Letter | 1-Letter | Category | Mol. Weight | Essential | Codons |
|---|---|---|---|---|---|---|
| Alanine | Ala | A | Aliphatic nonpolar | 89.1 Da | Non-essential | GCU, GCC, GCA, GCG |
| Arginine | Arg | R | Basic polar | 174.2 Da | Conditionally essential | CGU, CGC, CGA, CGG, AGA, AGG |
| Asparagine | Asn | N | Polar uncharged | 132.1 Da | Non-essential | AAU, AAC |
| Aspartate | Asp | D | Acidic polar | 133.1 Da | Non-essential | GAU, GAC |
| Cysteine | Cys | C | Polar uncharged | 121.2 Da | Conditionally essential | UGU, UGC |
| Glutamate | Glu | E | Acidic polar | 147.1 Da | Non-essential | GAA, GAG |
| Glutamine | Gln | Q | Polar uncharged | 146.2 Da | Conditionally essential | CAA, CAG |
| Glycine | Gly | G | Aliphatic nonpolar | 75.0 Da | Non-essential | GGU, GGC, GGA, GGG |
| Histidine | His | H | Basic polar | 155.2 Da | Essential | CAU, CAC |
| Isoleucine | Ile | I | Aliphatic nonpolar | 131.2 Da | Essential | AUU, AUC, AUA |
| Leucine | Leu | L | Aliphatic nonpolar | 131.2 Da | Essential | UUA, UUG, CUU, CUC, CUA, CUG |
| Lysine | Lys | K | Basic polar | 146.2 Da | Essential | AAA, AAG |
| Methionine | Met | M | Aliphatic nonpolar | 149.2 Da | Essential | AUG |
| Phenylalanine | Phe | F | Aromatic nonpolar | 165.2 Da | Essential | UUU, UUC |
| Proline | Pro | P | Aliphatic nonpolar | 115.1 Da | Non-essential | CCU, CCC, CCA, CCG |
| Serine | Ser | S | Polar uncharged | 105.1 Da | Non-essential | UCU, UCC, UCA, UCG, AGU, AGC |
| Threonine | Thr | T | Polar uncharged | 119.1 Da | Essential | ACU, ACC, ACA, ACG |
| Tryptophan | Trp | W | Aromatic nonpolar | 204.2 Da | Essential | UGG |
| Tyrosine | Tyr | Y | Aromatic polar | 181.2 Da | Conditionally essential | UAU, UAC |
| Valine | Val | V | Aliphatic nonpolar | 117.1 Da | Essential | GUU, GUC, GUA, GUG |
Frequently Asked Questions
How many amino acids are there?
There are 20 standard amino acids encoded by the genetic code. Two additional amino acids — selenocysteine and pyrrolysine — are considered the 21st and 22nd amino acids as they are incorporated by specific mechanisms in some organisms.
What are the 9 essential amino acids?
The nine essential amino acids are Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, and Valine. They must be obtained from dietary protein because the human body cannot synthesise them in adequate amounts.
What is a complete protein?
A complete protein contains all nine essential amino acids in adequate proportions. Animal proteins (meat, eggs, dairy, fish) are complete proteins. Soy and quinoa are complete plant proteins that provide all nine essential amino acids from a single source.
What amino acid is the start codon?
AUG codes for methionine — every protein begins with methionine at the N-terminus though it is often removed by post-translational processing in the final mature protein.
What is the difference between essential and non-essential amino acids?
Essential amino acids cannot be synthesised by the human body in sufficient quantities and must come from food. Non-essential amino acids can be made by the body from other metabolic intermediates such as glucose and other amino acids.
What is the smallest amino acid?
Glycine is the smallest amino acid — its side chain is just a single hydrogen atom giving it no chirality and maximum flexibility in protein chains. This unique property makes glycine essential in tight structural positions such as every third residue in collagen.
What amino acids are in collagen?
Collagen is unusually rich in glycine (every third residue), proline, and hydroxyproline. Glycine's small size allows it to fit in the tight core of the collagen triple helix structure, while proline and hydroxyproline provide the rigidity and stability of the helix.
What is the role of cysteine in protein structure?
Cysteine contains a sulphur-containing thiol group that can form disulphide bonds with other cysteine residues. These covalent cross-links stabilise protein tertiary structure and are critical in antibodies, insulin, and many extracellular proteins where structural rigidity is required.