peptides with COA

Reference

Amino acid reference

The twenty standard amino acids that make up peptides, with their one- and three-letter codes, average residue mass, charge class, and hydropathy. These are the same values the peptide property calculator uses under the hood.

Amino acid 3-letter 1-letter Residue mass Class Hydropathy
Alanine Ala A 71.08 Da Nonpolar +1.8
Arginine Arg R 156.19 Da Basic (+) −4.5
Asparagine Asn N 114.10 Da Polar −3.5
Aspartic acid Asp D 115.09 Da Acidic (−) −3.5
Cysteine Cys C 103.14 Da Polar (thiol) +2.5
Glutamic acid Glu E 129.12 Da Acidic (−) −3.5
Glutamine Gln Q 128.13 Da Polar −3.5
Glycine Gly G 57.05 Da Nonpolar −0.4
Histidine His H 137.14 Da Basic (+) −3.2
Isoleucine Ile I 113.16 Da Nonpolar +4.5
Leucine Leu L 113.16 Da Nonpolar +3.8
Lysine Lys K 128.17 Da Basic (+) −3.9
Methionine Met M 131.19 Da Nonpolar +1.9
Phenylalanine Phe F 147.18 Da Aromatic +2.8
Proline Pro P 97.12 Da Nonpolar −1.6
Serine Ser S 87.08 Da Polar −0.8
Threonine Thr T 101.11 Da Polar −0.7
Tryptophan Trp W 186.21 Da Aromatic −0.9
Tyrosine Tyr Y 163.18 Da Aromatic, polar −1.3
Valine Val V 99.13 Da Nonpolar +4.2

Residue masses are average (monoisotopic differs slightly); a free peptide adds one water (18.02 Da). Hydropathy is the Kyte–Doolittle scale — positive is water-repelling (hydrophobic), negative is water-loving.

How to read the table

  • 1- / 3-letterThe shorthand codes used to write sequences. A sequence like GEPPPGKPADDAGLV is just these one-letter codes strung together.
  • Residue massThe mass each amino acid contributes inside a chain (its free-form mass minus the water lost when it bonds). Sum them and add one water to get a peptide's molecular weight.
  • ClassThe side chain's character — nonpolar, polar, aromatic, basic (carries positive charge), or acidic (carries negative charge). This drives charge and solubility behavior.
  • HydropathyHow water-repelling (+) or water-loving (−) the residue is, on the Kyte–Doolittle scale; averaging it across a sequence gives GRAVY.

Common questions

What's the difference between residue mass and the amino acid's molecular weight?

Residue mass is what the amino acid contributes once it's joined into a chain — its free molecular weight minus one water, lost when the peptide bond forms. Molecular weight of a whole peptide is the residue masses summed plus one water.

Why do only some amino acids carry a charge?

Only certain side chains ionize: aspartate and glutamate tend to carry a negative charge; lysine, arginine, and histidine a positive one. The rest are neutral. The balance at a given pH is what the property calculator's net-charge and pI figures track.

Are these monoisotopic or average masses?

Average — the mass weighted across natural isotopes, which is what's typically used for molecular weight. Monoisotopic masses (used in mass spectrometry) are slightly lower.