Genetic Code

I work in a big Life Sciences institute at the University of Dundee. The building has a huge glass atrium entrance with a stained glass panel, depicting the A T G C of the genetic code that makes up our DNA, running to 3-4 stories high.
The A T G C stand for the 4 different nucleotides adenine, thymine, guanine and cytosine that make up the DNA which contains the genetic instructions used in the development and functioning of all known living organisms.