20 essential amino acids
Image reference
Each amino acid contains an "amine" group (NH3) and a "carboxy" group (COOH)
(shown in black in the diagram).
The amino acids vary in their side chains (indicated in blue in the
diagram).
The eight amino acids in the orange area are nonpolar and
hydrophobic.
The other amino acids are polar and hydrophilic ("water loving").
The two amino acids in the magenta box are acidic ("carboxy"
group in the side chain).
The three amino acids in the light blue box are basic ("amine" group
in the side chain).
Major contributions by
George Gamow (1904-1968), Russian-born American physicist
who proposed the "Big Bang Theory".
Left: George Gamow in 1948. Middle:
Early jottings by Gamow.
Right: Two competing coding hypotheses.
Image references.