Amino Acids

Amino acids are organic compounds that contain a carboxyl ($-COOH$) and amino ($-NH_2$).

Proteinogenic Amino Acids

Some of them make proteins; we call those proteinogenic amino acids. There are 20 encoded naturally by DNA, and two more that can be made synthetically (selenocysteine and pyrrolysine).

Non-Proteinogenic Amino Acids

There are also non-proteinogenic amino acids, and these outnumber their proteinogenic counterparts 5+:1. For example, Non-Ribosomal Peptides are made up of non-proteinogenic amino acids.