betterfuture

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Feb 16, 2016
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So the reason why the new dNTP's are added at the 3-OH group of the growing template strand is because of the ease of having a nucleophilic reaction occur.

So suppose if we wanted to add the new nucleotide at the 5(PO4)3- end, could it happen it there were 2 added phosphate groups attached to that 5 phosphate end?
 

lpp06

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Sep 16, 2012
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Very interesting question


Check this video out - explanation on why 3' to 5' reactions don't occur en vivo at the end.

As to why DNA synthesis didn't evolve this way - I would surmise that adding phosphates to the primer section during synthesis is unfavorably because it would require the hydrolysis of 2 ATP's per base pair added, which itself would probably require a different set of enzymes and would lengthen the time of this process. A longer DNA synthesis wouldn't be beneficial for things like cell division.

Chemically (someone correct me if I'm wrong - it's been awhile since orgo for me) - I think steric hindrance would have an effect on the Sn2 reaction and the diphosphate groups ability to leave.
 
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betterfuture

2+ Year Member
Feb 16, 2016
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Yeah. I had checked this video out.

At around 7:47, I think he forgot to include 2 more phosphate groups attached at the 5 end of the primer. So if we did add nucleotides at the 5 end of the primer, it could work but then again, I think I am thinking too much into this. Lol