- Oxidative deamination of 5-methylcytosine yields thymine. This will
pair with adenine rather than guanine during DNA replication.
- Nucleosides, nucleotide and bases with unusual base-pairing properties, or which serve as chain-termination agents will interfere with viral reproduction, and cause lethal mutation and/or truncation of the viral DNA during replication.
- Reverse-transcriptase PCR requires an RNA template, and for the reasons mentioned in the text, RNA is far less stable than DNA. Cells also produce many RNAses to degrade viral RNA, and these can also pose a problem during purification of the RNA.
- Both purines and pyrimidines are synthesised partly from aspartate. Purines also contain bits of other amino acids; the rest of a pyrimidine comes from carbamoyl phosphate. Purines are synthesised on ribose; pyrimidines are attached to ribose after synthesis. Purines rely on C1 metabolism, and can be targeted by methotrexate; pyrimidines cannot.