AAT Bioquest

What are the categories of amino acids?

Posted April 14, 2022


Amino acids are composed of a carbon atom, a hydrogen atom, a carboxyl group along an amino group, and a variable group called the “R” group. The variable "R" group is what distinguishes the different amino acid categories. Amino acids can be classified into four categories – polar, nonpolar, positively charged, or negatively charged - depending on the properties of the “R” group in each amino acid.

  • Polar amino acids have a hydrophilic “R” group that seeks contact with water and aqueous solutions. Cysteine, Glutamine, and Asparagine are some amino acids that come under the polar category.
  • Nonpolar amino acids have a hydrophobic “R” group and avoid contact with water and other liquids. Glycine, Tryptophan, and Alanine are some amino acids that come under the nonpolar category.
  • Positively charged amino acids are also called polar basic amino acids. Arginine, Histidine, and Lysine come under the category of positively charged amino acids. 
  • Negatively charged amino acids are also called polar acidic amino acids. Glutamate and Aspartate are negatively charged amino acids.
Additional resources

Determination of free amino acids, organic acids, and nucleotides in 29 elegant spices

Amplite™ Colorimetric Aspartate Aminotransferase (AST) Assay Kit