Tag Archives: pka

Amino Acid Reference Chart

A reference chart for the 20 human amino acids and associated properties. 

Code (1): Refers to each amino acid’s single letter code

Code (3): Refers to each amino acid’s three letter code

pKa: Refers to the negative logarithm of thedissociation constant for the functional group of the amino acid. Also known asthe pH below which the group is protonated. This can change based on the environment of the amino acid.

pI: Refers to the pH at the amino acid isoelectric point

Property: Often divided into “polar” and “nonpolar” groups; here we provided a more descriptive note on the amino acid functional group chemical and charge properties.

Essential: Refers to whether the amino acid must be obtained from the diet (essential) or can be synthesized in the body (non-essential).

Name Code (1) Code (3) pKa pI Property Essential
Alanine Ala A   6.00 Alipathic Non-essential
Asparagine Asn N   5.41 Amidic Non-essential
Asp D 3.65 2.77 Acidic Non-essential
Arginine Arg R 12.48 10.76 Basic Non-essential
Cysteine Cys C   5.07 Sulfuric Non-essential
Glu E 4.25 3.22 Acidic Non-essential
Glutamine Gln Q   5.65 Amidic Non-essential
Glycine Gly G   5.97 Alipathic Non-essential
Histidine His H 6.00 7.59 Basic Essential
Isoleucine Ile I   6.02 Alipathic Essential
Lysine Lys K 10.53 9.74 Basic Essential
Leucine Leu L   5.98 Alipathic Essential
Methionine Met M   5.74 Sulfuric Essential
Phe F   5.48 Aromatic Essential
Proline Pro P   6.30 Alipathic Non-essential
Serine Ser S   5.68 Hydroxylic Non-essential
Threonine Thr T   5.60 Hydroxylic Essential
Trp W   5.89 Aromatic Essential
Tyrosine Tyr Y 10.07 5.66 Aromatic Non-essential
Valine Val V   5.96 Alipathic Essential