Amino Acid
Amino acids are the 20 standard organic molecules that serve as the building blocks of peptides and proteins. They are joined end-to-end by peptide bonds to form chains of varying length and function.
Overview
Each amino acid consists of a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R group) that determines its chemical properties. The 20 standard amino acids differ only in their side chains, which can be polar, nonpolar, acidic, or basic — properties that dictate how a peptide folds and interacts with receptors. When two amino acids join, the carboxyl group of one reacts with the amino group of the other to form a peptide bond, releasing a water molecule in the process. The sequence of amino acids in a chain (its primary structure) determines the peptide's three-dimensional shape and biological activity.
Related Terms
Frequently asked questions
How many standard amino acids are there?+
There are 20 standard amino acids encoded by the human genetic code, though some peptides contain modified or non-natural amino acids to enhance stability or activity.
Are amino acid supplements the same as peptides?+
No. Amino acid supplements provide free individual amino acids, while peptides are chains of amino acids already joined by peptide bonds.
Which amino acids are essential?+
Nine amino acids (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine) are considered essential because the body cannot synthesize them and they must be obtained from diet.