All life on earth uses DNA with four types of base molecules arranged in a “double helix” to encode information as sequences of Adenine-Thymine (A-T) and Cytosine-Guanine (C-G) pairs. Because A pairs only with T and C only pairs with G, DNA can be split into two halves and then each half may be completed so that two double helices with the same information can be obtained. Nature also uses the “genetic code” to translate the information in DNA into specific amino acids via its molecular machinery that assembles proteins in the correct sequence.
Now scientists have doubled the number of base pairs of DNA by adding four synthetic ones to the original four natural ones. Four new base molecules S (a Pseudo-T), B (a Pseudo-B), Z (a Pseudo-C), and P (a Pseudo-G) have been created so that S only pairs with B and Z pairs only with P. Now you have twice as many options as you had before and so this “hachimoji” (eight letter) DNA can have much greater information density. Plus if you re-engineer the molecular machinery to use these new bases you can have a brand new extended genetic code to build all sorts of synthetic proteins.