How many amino acids are there in total?

The total number of standard amino acids used in the synthesis of proteins is 20. These amino acids are the building blocks of proteins and play a crucial role in various biological processes. Each amino acid has a specific side chain, or R group, that determines its unique characteristics and chemical properties.

Additionally, while there are other amino acids that exist and are involved in different biological functions, they are not included in the standard set used for protein synthesis. For instance, certain amino acids like selenocysteine and pyrrolysine do exist, which brings the count to 22, but they are not part of the main group of amino acids directly coded by the genetic code for proteins.

Thus, when considering the standard amino acids essential for forming proteins, the correct answer is 20, which encompasses the widely recognized set used in biological processes.