[Sam Brown (OP)]

Shafiqullah has asked:

"Why do we not use the letter A,B,C and D, instead of A,C,G and T, for DNA?"

Can anyone help answer?

[chiralSPO]

A, C, G, and T are abbreviations for the names of the molecules. See here: https://en.wikipedia.org/wiki/Nucleoside

[evan_au]

The bases of RNA are similar to DNA, except RNA contains Uracil (U) in place of Thymine (T).

The movie GATTACA managed to construct an almost-pronounceable name from the names of the DNA bases. It is set in a dystopian society where DNA sequencing is extremely cheap and readily available.
See: https://www.imdb.com/title/tt0119177/

[AnnaSmith]

People above gave good answers, so thanks!