Question

Could someone please explain this one?
A is used as antiviral drug which acts by interfering with DNA synthesis. B has no such analogous activity. Explain this using the fact that DNA is replicated in 5' to 3' direction

Answer 1

Here is the snapshot of the question

Answer 2

Can you see the difference at carbon position 3 and 5 for both A and B?

Let see the A drug. At carbon position 3, N2 is attached here. At carbon position 5, OH is attached here.

Then let see the B drug. At carbon position 3, OH is attached here. At carbon position 5, N2 is attached here.

The drug A and B can be used to make nucleotide because they are nucleoside (base and sugar). To make nucleotide, you need to add phosphate group on the OH group of the sugar. So, at drug A phosphate group is added at C5 while drug B is on C3.

DNA is replicated from 5' to 3' direction. In other words, 3' keep growing as you add nucleotides on the 3' end. Nucleotides are joined together by phosphodiester bond between 5' and 3' carbon atoms to form nucleic acid. For drug A, it can be added to the growing 3' end because the phosphate is on the C5. But for drug B, the phosphate group is on C3 so it cannot be added to the growing 3' end.

I hope this helps.

Answer 3

Great! Thanks for the explanation !