If RNA was first, they reasoned, it should be possible to build an RNA molecule out of the ingredients lying about in the primordial kitchen. But here chemists ran into problems. When chemists tried to brew RNA in their chemistry beakers, they succeeded only in creating a tangled mess. There had to be a predecessor. The amino acid is the other strong contender for the job of first living molecule.
Amino acids are very simple in structure, and very necessary for life.
They are the basic units of proteins, which do all sorts of useful work inside the cell. One thing proteins do particularly well is act as enzymes, catalyzing other chemical reactions. The first team to do it was Stanley Miller and Harold Urey at the University of Chicago in 1953. But if making amino acids was easy, making proteins proved almost impossible. To make a protein, the amino acids must first be hooked onto each other in a very specific order in a long chain called a peptide.