There are 20 standard amino acids that are used to build proteins in most organisms, though many more distinct amino acids exist in nature. The core set that is encoded by the genetic code and most commonly referenced in biology is 20 (often called proteinogenic amino acids).
Key points
- Protein-building set: 20 standard amino acids are encoded in the genetic code and incorporated into proteins across most life forms.
- Additional examples: Beyond the standard 20, other amino acids exist in nature (e.g., selenocysteine and pyrrolysine are incorporated in some organisms); hundreds of non-proteinogenic amino acids have been identified in nature, but they are not part of the canonical protein-building set.
- Contextual nuance: Some sources also discuss a broader count (approximately 500 amino acids identified in nature), but the widely cited protein-building set for polypeptides is 20, with occasional inclusion of selenocysteine and pyrrolysine as the 21st and 22nd in specific contexts.
If you want, I can pull precise lists of the 20 standard amino acids and also note which ones are sometimes considered extra (selenocysteine, pyrrolysine) and where they appear.
