14. Compounds that generate nitrous acid (such as nitrites, nitrates, and nitrosamines) change DNA molecules by: a. breakage of phosphodiesterbonds. b. deamination of bases. c. depurination. d. formation of thymine dimers. e. transformation of A T. 15. What is the difference between a nucleoside and a nucleotide? 16. Draw the structure of your favorite purine-pyrimidine base pair as found in the Watson- Crick double-helical structure of DNA. Include all hydrogen bonds. 17. Shown below is the structure of _ Draw the structure of its canonical base pair and mark which atoms participate in hydrogen bonds. Draw and name the (deoxy) nucleoside corresponding to this base.