Reference
The 20 amino acids: codes chart
Every peptide and protein is written using these 20 letters.
| Amino acid | 3-letter | 1-letter | Mass (g/mol) | Group | Essential |
|---|
Mass is for the free amino acid. Inside a chain, each one weighs 18.02 g/mol less, because it lost a water molecule when it joined.
What "essential" means
Nine amino acids are essential: the human body can't make them, so they have to come from food. They are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. The other eleven the body can build itself.
Why some codes look odd
Most one-letter codes match the first letter of the name, like G for glycine. Where several names share a letter, others got creative: K for lysine (L was taken by leucine), W for tryptophan (often remembered as "tWyptophan"), F for phenylalanine ("fenylalanine"), D for aspartate and E for glutamate.
The groups
- Nonpolar amino acids avoid water and tend to sit inside folded proteins.
- Polar amino acids are comfortable in water.
- Positive (lysine, arginine, histidine) and negative (aspartate, glutamate) carry an electric charge, which helps peptides and proteins bind to other molecules.
Put the codes to use in the molecular weight calculator.