An amino acid
. A nonessential
amino acid, you might be relieved to know. Glycine
is the simplest possible amino acid, and if you chip a hydrogen
ion off either end of one (a sharp stone adze or a kitchen knife will do) you can stick two of them together, and it's still an amino acid, called either diglycine
. The chemical structure of the glycine molecule
admits indefinite chaining of this kind*.
An amino acid has the general formula CHR(NH2)COOH. That is, a pivotal carbon atom has an amino radical NH2, a carboxyl radical COOH, and some other distinguishing radical R. Glycine, the simplest case, has plain H for its R. The standard symbol for glycine is Gly.
There are two different glycyl ions: I don't know what the proper chemical names for them are, but you can either knock a hydrogen off the amino to give CHR(NH-)COOH or you can knock a hydroxy off the carboxyl to give CHR(NH2)CO+. The combination of these two gives common or garden glycylglycine. These are symbolized Gly- and -Gly.
A third possibility is to knock off both the H+ and the OH- (these combine to give water so put some towels down first), and this gives you another ion, -Gly-. This one can go in the middle of the other two. Repeat to taste.
Glycylglycylglycylglycylglycine has a Gly- at one end, three lots of -Gly- in the middle, and a -Gly at the far end.
Reaction rates for glycylglycylglycylglycylglycine may be found at
-- in particular EAQ1263.HTM and EAQ1264.HTM, but the whole long list is interesting if you like that sort of thing.
* I can't swear to the indefinite: there might well be some stereochemical restriction that prevents it polymerizing to arbitrary length.