Indeed, that's exactly the solution I had in mind, well done.
I'd got it 90% done when I realised that I couldn't make words for two of them - so i cheated slightly by putting in a small town in Croatia, and leaving you to find the one I couldn't do anything with.
An explanation of the hints:
The solution is from the field of science. The necessary information is in Wikipedia, though if you know which page to look at you've already solved the puzzle.
Specifically, the page "Proteinogenic amino acid", which will give you the exact list needed to complete the puzzle.
Each of the three letter items represents something. 20 of them can also be represented by three letters in a different way - some of them in more than one way - and 2 cannot directly.
The other way of representing them is by how they are encoded as DNA - also three letters but only using G A T and C (plus wildcards). 20 of them are represented by a three base-pair code, the other two are represented more indirectly.
F---WATTER ought to be easy to find the missing letters. There's a connection between Jurassic Park (the first film) and what the three letters represent here. If the plan had worked, there wouldn't have been any more films...
FLYSWATTER, of course, giving LYS - Lysine. The "Lysine contingency" was supposed to make Jurassic Park's dinosaurs dependent on human provided food so escaped dinosaurs couldn't survive. If it worked as planned, when the park was abandoned the dinosaurs would have died (and the sequels would not exist). Needless to say, it didn't work....