1) Guanine (G) is one of four chemical bases in DNA, with the other three being adenine (A), cytosine (C), and thymine (T). Within the DNA molecule, guanine bases located on one strand form chemical bonds with cytosine bases on the opposite strand. The sequence of four DNA bases encodes the cell's genetic instructions.

2) A purine base (C5H5N5O) that codes genetic information in the polynucleotide chain of DNA or RNA.