Why are amino acids named amino acids?

Question

When learning about amino acids, the primary things that were pointed out were that they had an amino group and a carboxyl group, and side chain that varies from one to the other.

The amino group of one can attach to the carboxyl group of another, making a peptide bond and water.

Both groups are clearly important, but what is it about the amino group that that's what goes in the name "amino acid"? Is the amino group in some way more important? Is it just something about the way/order in which they were discovered/identified that the name just came about?

Why amino acid? Not carboxyl acid, or some mix of the two, or something else?

Answer 1

When learning about amino acids, the primary things that were pointed out were that they had an amino group and a carboxyl group...

Why amino acid? Not carboxyl acid, or some mix of the two, or something else?

You stated why it is called an amino acid, the name comes from the amine (amino) and the carboxylic acid (carboxyl group).

Amines are weak bases, so the acid portion of the name must come from the carboxylic acid.

Answer 2

You might think that the term "amino acid" comes from the more systematic names of these molecules, where the amine is a substituent.

Common name        systematic name
glycine            2-aminoethanoic acid
alanine            2-aminopropanoic acid
valine             2-amino-3-methylbutanoic acid
cysteine           2-amino-3-mercaptopropanoic acid
serine             2-amino-3-hydroxypropanoic acid

In all of these names "amino" precedes "acid".

You would be wrong!

"Amino acid" apparently entered the English lexicon in 1898, long before IUPAC reared its systematic nomenclature head. It is likely then, though I was not there, that "amino acid" came about from two considerations:

• We were already probably using the prefix "amino-" to denote molecules with nitrogen groups in them.
• "Amino acid" was probably easier to pronounce than other possible combinations.

Answer 3

By the way, interestingly, most of the amino acids in the normal conditions are not acids nor amines, but rather “inner salts”, i.e. dipolar ions, i.e. ‘zwitterions’, $\ce{H3N+-CH(R)-COO-}$, i.e. “inner ammonium carboxylate salts”, rather than aminocarboxylic acids.