question 310 in bio destroyer

[brightsmiles9]

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Theres a picture of AZT and the question says why could this drug possibly interfere with DNA replication?

ans: The molecule lacks and OH group at C-3, thus no nucleophile is present to react with the 5 triphosphate group of a growing polynucleotide chain.

Can anyone explain that to me??

 

[GOLF]

yeah i think i know what it means- at the 3rd carbon, there is no group that can form a bond with another nucleotide- you need to have an -OH group so that another nucleotide can 'link' to it and thus keep the chain growing in length. if you slap this AZT molecule on there, no other nucleotides can link on (because of the N3 group sitting on C-3), and synthesis of the chain cannot continue.

remember DNA is synthesized 5' to 3' so if the 3' end lacks a nucleophile, there is no affinity for another nucleotide, and synthesis will come to a halt. skim this and you'll be good on dna synthesis - http://en.wikipedia.org/wiki/DNA_replication
wikipedia is a good resource for things you might need some clearing up on - they do a good job of organizing biology topics too.