Amino acids are a type of chemical compound. An acid that contains molecules of nitrogen, oxygen, carbon and hydrogen, sequences of amino acids in protein are encoded in DNA, making these the structural building blocks of carbon-based lifeforms.
The first long-chain amino acid molecules on Earth formed billions of years ago as part of the planet's evolutionary process. According to Q, pre-historic France was the site of this occurrence. (TNG episode & novelization: All Good Things...)
Basic amino acids were part of the many foodstuffs available in the Federation in the 23rd century. Mars Foods Incorporated advertised themselves as a supplier of amino acids in Spacelanes, a periodical publication in the late 23rd century. (FASA RPG module: Spacelanes: The Magazine of Interstellar Trade)
Captain Jean-Luc Picard had a recipe for a warm milk toddy that was passed on by his Aunt Adele. While Picard valued the flavor and nostalgia of the family recipe, Doctor Beverly Crusher reminded him that the natural sedative effect was a simple reaction of heat-activated amino acids and lactose. (TNG episode: "Schisms")
At some point prior to the year 2367, the Klingon scientist J'Dan began using a method of encoding computer information in amino acid sequences. J'Dan injected himself and others with the amino acid data, and used the process to send sensitive information to the Romulan Star Empire. (TNG episode: "The Drumhead")
In the 2370s decade, Julian Bashir was involved in scientific research to support a theory that quantum resonance played a factor in the replication of prions, while conventional wisdom held that prion replication was purely a function of disulfide shuffling and amino acid re-sequencing. (DS9 episode: "Nor the Battle to the Strong")
In the year 2373 on the Nechani homeworld, Kathryn Janeway was bitten by a nesset. The breakdown of the nesset toxin caused an amino acid to form in her body, blocking neurotransmitters and causing hallucinations. (VOY episode: "Sacred Ground")