- Purines – 2 double rings
- – GUANINE
- Pyrimidines – 1 ring
- Order of bases contains the ‘code’ to make proteins
- In a DNA molecule it must be made of a purines and a pyrimdines which makes it an exact length g if it was 2 purines it would be too long and if it was 2 pyrimidines it would be too short!