Amino acids are the building blocks of proteins. About how many kinds of amino acids are there?
There are 20 standard amino acids that are commonly found in the proteins of living organisms. These amino acids are encoded directly by the universal genetic code and are:
1. Alanine (Ala, A)
2. Arginine (Arg, R)
3. Asparagine (Asn, N)
4. Aspartic acid (Asp, D)
5. Cysteine (Cys, C)
6. Glutamine (Gln, Q)
7. Glutamic acid (Glu, E)
8. Glycine (Gly, G)
9. Histidine (His, H)
10. Isoleucine (Ile, I)
11. Leucine (Leu, L)
12. Lysine (Lys, K)
13. Methionine (Met, M)
14. Phenylalanine (Phe, F)
15. Proline (Pro, P)
16. Serine (Ser, S)
17. Threonine (Thr, T)
18. Tryptophan (Trp, W)
19. Tyrosine (Tyr, Y)
20. Valine (Val, V)
In addition to these standard amino acids, there are many other non-standard amino acids, including those incorporated into proteins by unique cellular mechanisms (like selenocysteine and pyrrolysine) as well as those that can be created through post-translational modifications after the protein has been synthesized.