G
Glycine
Gly · G · Glycine / proline
- Formula
- C₂H₅NO₂
- Mol. weight
- 75.07 g/mol
- Dietary
- Conditionally essential
Smallest amino acid; about one in three residues of collagen; an inhibitory neurotransmitter.
The 20 amino acids
The building blocks of every peptide and protein. Structures, codes, side-chain classes, dietary status, formulas and molecular weights, with links to each PubChem record.
HydrophobicPolarPositive chargeNegative chargeGlycine / proline
A
Alanine
Ala · A · Hydrophobic
- Formula
- C₃H₇NO₂
- Mol. weight
- 89.09 g/mol
- Dietary
- Nonessential
Small and simple; carries nitrogen from muscle to liver in the glucose–alanine cycle.
V
Valine
Val · V · Hydrophobic
- Formula
- C₅H₁₁NO₂
- Mol. weight
- 117.15 g/mol
- Dietary
- Essential
One of the three branched-chain amino acids (BCAAs).
L
Leucine
Leu · L · Hydrophobic
- Formula
- C₆H₁₃NO₂
- Mol. weight
- 131.17 g/mol
- Dietary
- Essential
Branched-chain amino acid that signals cells, via mTOR, to build protein.
I
Isoleucine
Ile · I · Hydrophobic
- Formula
- C₆H₁₃NO₂
- Mol. weight
- 131.17 g/mol
- Dietary
- Essential
Branched-chain amino acid; same formula as leucine, different shape.
P
Proline
Pro · P · Glycine / proline
- Formula
- C₅H₉NO₂
- Mol. weight
- 115.13 g/mol
- Dietary
- Conditionally essential
Its ring locks the backbone and creates kinks; abundant in collagen.
F
Phenylalanine
Phe · F · Hydrophobic
- Formula
- C₉H₁₁NO₂
- Mol. weight
- 165.19 g/mol
- Dietary
- Essential
Aromatic; the body converts it to tyrosine. Restricted in phenylketonuria (PKU).
W
Tryptophan
Trp · W · Hydrophobic
- Formula
- C₁₁H₁₂N₂O₂
- Mol. weight
- 204.23 g/mol
- Dietary
- Essential
Largest amino acid; precursor of serotonin, melatonin and niacin.
M
Methionine
Met · M · Hydrophobic
- Formula
- C₅H₁₁NO₂S
- Mol. weight
- 149.21 g/mol
- Dietary
- Essential
Contains sulfur; starts nearly every newly made protein.
S
Serine
Ser · S · Polar
- Formula
- C₃H₇NO₃
- Mol. weight
- 105.09 g/mol
- Dietary
- Nonessential
Small and polar; a common site where cells attach phosphate groups.
T
Threonine
Thr · T · Polar
- Formula
- C₄H₉NO₃
- Mol. weight
- 119.12 g/mol
- Dietary
- Essential
Polar; another common phosphorylation site.
C
Cysteine
Cys · C · Polar
- Formula
- C₃H₇NO₂S
- Mol. weight
- 121.16 g/mol
- Dietary
- Conditionally essential
Contains sulfur; forms disulfide bridges and is part of glutathione.
Y
Tyrosine
Tyr · Y · Polar
- Formula
- C₉H₁₁NO₃
- Mol. weight
- 181.19 g/mol
- Dietary
- Conditionally essential
Aromatic; precursor of dopamine, adrenaline and thyroid hormones.
N
Asparagine
Asn · N · Polar
- Formula
- C₄H₈N₂O₃
- Mol. weight
- 132.12 g/mol
- Dietary
- Nonessential
Polar amide; the attachment point for many sugar chains on proteins.
Q
Glutamine
Gln · Q · Polar
- Formula
- C₅H₁₀N₂O₃
- Mol. weight
- 146.15 g/mol
- Dietary
- Conditionally essential
The most abundant free amino acid in blood; fuel for gut and immune cells.
D
Aspartic acid
Asp · D · Negative charge
- Formula
- C₄H₇NO₄
- Mol. weight
- 133.10 g/mol
- Dietary
- Nonessential
Negatively charged; feeds the urea cycle and nucleotide building.
E
Glutamic acid
Glu · E · Negative charge
- Formula
- C₅H₉NO₄
- Mol. weight
- 147.13 g/mol
- Dietary
- Nonessential
Negatively charged; as glutamate, the main excitatory neurotransmitter.
K
Lysine
Lys · K · Positive charge
- Formula
- C₆H₁₄N₂O₂
- Mol. weight
- 146.19 g/mol
- Dietary
- Essential
Positively charged; frequently modified, for example on histones.
R
Arginine
Arg · R · Positive charge
- Formula
- C₆H₁₄N₄O₂
- Mol. weight
- 174.20 g/mol
- Dietary
- Conditionally essential
Positively charged; precursor of nitric oxide and part of the urea cycle.
H
Histidine
His · H · Positive charge
- Formula
- C₆H₉N₃O₂
- Mol. weight
- 155.16 g/mol
- Dietary
- Essential
Imidazole ring; precursor of histamine.
No amino acids match that search.
Reference table
All 20 at a glance. Molecular weights are average values for the free amino acid.
| Amino acid | Code | Side-chain class | Dietary status | Formula | MW (g/mol) | |
|---|---|---|---|---|---|---|
| G | Glycine | Gly | Glycine / proline | Conditionally essential | C₂H₅NO₂ | 75.07 |
| A | Alanine | Ala | Hydrophobic | Nonessential | C₃H₇NO₂ | 89.09 |
| V | Valine | Val | Hydrophobic | Essential | C₅H₁₁NO₂ | 117.15 |
| L | Leucine | Leu | Hydrophobic | Essential | C₆H₁₃NO₂ | 131.17 |
| I | Isoleucine | Ile | Hydrophobic | Essential | C₆H₁₃NO₂ | 131.17 |
| P | Proline | Pro | Glycine / proline | Conditionally essential | C₅H₉NO₂ | 115.13 |
| F | Phenylalanine | Phe | Hydrophobic | Essential | C₉H₁₁NO₂ | 165.19 |
| W | Tryptophan | Trp | Hydrophobic | Essential | C₁₁H₁₂N₂O₂ | 204.23 |
| M | Methionine | Met | Hydrophobic | Essential | C₅H₁₁NO₂S | 149.21 |
| S | Serine | Ser | Polar | Nonessential | C₃H₇NO₃ | 105.09 |
| T | Threonine | Thr | Polar | Essential | C₄H₉NO₃ | 119.12 |
| C | Cysteine | Cys | Polar | Conditionally essential | C₃H₇NO₂S | 121.16 |
| Y | Tyrosine | Tyr | Polar | Conditionally essential | C₉H₁₁NO₃ | 181.19 |
| N | Asparagine | Asn | Polar | Nonessential | C₄H₈N₂O₃ | 132.12 |
| Q | Glutamine | Gln | Polar | Conditionally essential | C₅H₁₀N₂O₃ | 146.15 |
| D | Aspartic acid | Asp | Negative charge | Nonessential | C₄H₇NO₄ | 133.10 |
| E | Glutamic acid | Glu | Negative charge | Nonessential | C₅H₉NO₄ | 147.13 |
| K | Lysine | Lys | Positive charge | Essential | C₆H₁₄N₂O₂ | 146.19 |
| R | Arginine | Arg | Positive charge | Conditionally essential | C₆H₁₄N₄O₂ | 174.20 |
| H | Histidine | His | Positive charge | Essential | C₆H₉N₃O₂ | 155.16 |
“Conditionally essential” amino acids are normally made by the body but may need to come from the diet during growth, illness or injury. Classifications vary slightly between textbooks. Sources: PubChem (National Library of Medicine); standard biochemistry references.
Cite this page
VALREXA Biosciences. (2026, November 7). The 20 amino acids: structure, classes and roles. VALREXA Biosciences. https://valrexa.com/amino-acids.html
APA style · Last reviewed November 7, 2026 · Our editorial standards