"but I'm utterly amazed at how simple this _appears_."

Biology is a funny old thing. You can look at that concise description - the orange and so on blocks of a few letters and a few short groupings.

Now ATCG are basic building blocks but they consist of quite a lot of stuff. I think it's a bit more complex than that because this is RNA not DNA so ATCG might not be quite right. Each of those bases are horrifically complicated depending on scale. Search "ATCG" - this is a good start: https://en.wikipedia.org/wiki/Nucleobase

Now dive into one of those bases and decompose it to its constituent atoms. Now look at the maths around this stuff. It gets quite complicated, quite quickly.

That said, the fact that a bloody complicated thingie can be described so concisely is absolutely amazing and as you say it looks so simple.