1. The problem statement, all variables and given/known data The problem was to tell how many hydrogen bonds there are between cytosine and guanine. and I know there are three. http://study.com/cimages/multimages/16/Cytosine_Guanine_base_pair.png But I think I might be misunderstanding the hydrogen bond concept. I thought that hydrogen bonds only formed between O, F and N when they are also bond to H atom. And therefor CO2 fx does not form hydrogen bond with water as the oxygen atoms in the CO2 are not bonded to H atom. In the cytosine-Guanine there is a hydrogen bond between Oxygen atom and NH2 but the Oxygen atom is only bond to Carbon, so why is there a hydrogen bond? And N makes hydrogen bond with NH but the N is only bond to two C atoms please explain.