Several artificial nitrogenous bases, called base analogues, can be taken up by cells, converted to nucleotides, and incorporated into nucleic acids. They are often potent mutagens, and some are used in cancer chemotherapy. Two such analogues are 5-bromouracil (5-BU), and 2-aminopurine (2-AP).
a) Draw 5-BU and 2-AP and show their bonding to the bases they are most likely to pair with
b) Draw tautomers for both bases. Under physiological conditions most of the bases exist as keto (amino) tautomer, but in 5-BU the bromine group shifts the equilibrium toward an enol form. Show how this shift might cause 5-BU to pair with the purine that you would not choose as most likely in part a).