DNA Replication Addition Occurs Via a Nucleophilic Attack Deoxyribonucleoside triphosphates, as we just stated, are the building blocks of DNA. Recall, furthermore, that a complete polynucleotide strand of DNA has only one phosphate group and that through this phosphate group each nucleotide is attached to the next. Why then is the substrate a triphosphate instead of just a monophosphate? The answer to this question lies in the chemistry underlying the addition of nucleotides to a growing daughter strand of DNA. While each nucleotide added to a growing DNA chain lacks an -OH group at its 2' position, it retains its 3' -OH. This hydroxyl group is used to attack the alpha phosphate group of an incoming nucleoside triphosphate. In the attack, the 3' -OH replaces the beta and gamma phosphates that are ejected from the complex as a pyrophosphate molecule. The result is the formation of the phosphodiester bond between the growing daughter strand and the next nucleotide. The 3' -OH of the newly added nucleotide is now exposed on the end of the growing
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This note was uploaded on 01/27/2012 for the course BIOLOGY BSC1005 taught by Professor Rodriguez during the Winter '09 term at Broward College.