Are amino acids other than the usual 20 amino acids found in proteins? If so, how are such amino acids produced?

Yes, apart from the usual 20 amino acids found in proteins, there are other amino acids that have been discovered. These non-standard amino acids are not commonly found in proteins, but they play important roles in various biological processes.

There are several ways in which non-standard amino acids can be produced. Here are three primary methods:

1. Post-translational modification: Some non-standard amino acids are generated through post-translational modification of the standard amino acids. During or after protein synthesis, enzymes can chemically modify specific amino acids to create new functional groups or alter the existing ones, resulting in non-standard amino acids.

2. Enzymatic conversion: Some organisms possess unique enzymatic pathways that can convert standard amino acids into non-standard ones. For example, in bacteria, an enzyme called pyrrolysyl-tRNA synthetase can incorporate the non-standard amino acid pyrrolysine into specific proteins.

3. Non-ribosomal peptide synthesis: In certain cases, non-standard amino acids are produced by specialized biosynthetic pathways known as non-ribosomal peptide synthesis (NRPS). NRPS operates independently of the ribosomal protein synthesis machinery and can incorporate non-standard amino acids into peptide chains.

It is worth noting that the discovery and study of non-standard amino acids are still ongoing, and new methods of their production may continue to be identified.