Before I ask my question, I would like to state that I am not a Biology student. I am actually a Chemistry student who has a small section on Biochemistry in his syllabus. Now, my problem lies with part (ii). Mechloroethamine obviously hold the DNA strands together and prevents the DNA helix from uncurling/unzipping. Hence, the very first stage in replication is impeded. How cis-platin affects DNA replication is eluding me. I know that Guanine normally forms 3 hydrogen bonds with Cytosine. However, it seems to be forming only one hydrogen bond in this case. Could someone prod me in the correct direction ?