You carry out a DNA replication reaction using a single-stranded DNA template, D

Question

You carry out a DNA replication reaction using a single-stranded DNA template, DNA polymerase, a primer, and the four deoxyribonucleoside triphosphates. You then add the nucleotide form of AZT (azidothymidine) to the reaction mixture. The structure of AZT is very similar to deoxythymidine; except that in AZT, the 3'-hydroxyl (OH) on the deoxyribose ring has been replaced by an azido (N3) group. a) What would you expect to happen to DNA replication when you add the AZT nucleotide to the reaction mixture? Briefly explain your reasoning. b) Why might AZT help individuals who have cancer?

Explanation / Answer

Answer:

a. When AZT (Azidothymidine) nucleotide is added to the reaction mixture the replication stops as the subsequent nucleotides will not be able to bind to the nitrogen (from azido group) of the AZT. Therefore chain termination will occur and replication would stop.

b. AZT will help patients with cancer because of following reasons: AZT which is an analog of deoxythiamidine has a higher affinity for reverse transcriptase than the deoxythiamidine nucleotide, so AZT will get preferentially incorporated into growing strand of DNA. Now since it doesn't contain the free 3'-hydroxyl group but instead contains the azido group, therefore, chain termination would occur and DNA replication will stop. This way the drug acts as a chain terminator of DNA synthesis and kills actively dividing cells and it may help treat individuals suffering from cancer.

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