What is the total number of standard amino acids used by living organisms?

Living organisms use a total of 20 standard amino acids for the synthesis of proteins, which are critical for various biological functions. Each of these amino acids is characterized by a unique side chain, and they combine in different sequences to form proteins, which ultimately determine an organism's structure, function, and metabolism.

The genetic code, consisting of codons, encodes for these 20 amino acids, making it fundamental to the process of translation during protein synthesis. This set of 20 amino acids is highly conserved across different forms of life, highlighting their importance in biological processes.

While there are additional amino acids that can be incorporated into proteins through post-translational modifications or are used in specific contexts (like non-standard amino acids), the standard 20 amino acids are universally recognized and used in the majority of protein synthesis across all living organisms.