Where does alkylation specifically occur on the guanine base for mono-functional alkylating agents?

Mono-functional alkylating agents specifically target the guanine base in DNA, and one of the key aspects of their action is the alkylation of specific sites on this base. The most common sites for alkylation on guanine are the nitrogen atom at position 7 and the oxygen atom at position 6.

When mono-functional alkylating agents react with guanine, the nitrogen at position 7 is primarily targeted because it can form a stable bond with the alkyl group, which can lead to DNA cross-linking or mispairing during DNA replication. This can ultimately cause disruptions in DNA synthesis and lead to mutations.

Additionally, alkylation at the oxygen at position 6 can also occur, although it is less common than the reaction at the nitrogen. This interaction can contribute to the overall effectiveness of these agents in targeting and damaging DNA.

Therefore, since both the nitrogen at position 7 and the oxygen at position 6 are sites of alkylation, the correct answer reflects that alkylation can occur at both these locations in the guanine base for mono-functional alkylating agents.