How many total amino acids are known in biochemistry?

In biochemistry, there are 20 standard amino acids that are universally used by organisms to build proteins. These 20 amino acids are characterized by their unique side chains, or R groups, which determine their individual properties and functions in protein structure and activity. This set is critical for the translation of genetic code into protein structure, as it is the basis of the genetic "alphabet" that forms the proteins necessary for life.

While variations do exist, such as selenocysteine and pyrrolysine, which are sometimes considered when discussing the total number of amino acids, these are categorized as special cases and are not included in the main list of standard amino acids. Hence, the significance of the 20 standard amino acids remains foundational in biochemistry and is critical for understanding protein synthesis and function.