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Old 01-05-2015
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Default I don't understand this in FA ?!

in FA 2014 P72
The triphosphate bond is the target of the 3' hydroxyl attack ??
what does this mean???

the triphosphate bond ,,does it mean the one on 5' ?
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Old 01-19-2015
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The DNA chain cannot continue to grow if it does not have a 3'-hydroxyl group, because this group is required to attack the phosphate of the next incoming deoxynucleotide during the formation of the phosphodiester bond.
eg. ziduvidine is a chain terminator by having a modified OH (replaces it with azide group) group that prevents further addition of the next nucleotide

and yes it means the triphosphate on the 5' end of the new upcoming nucleotide for bonding

Last edited by spasemaster; 01-19-2015 at 11:11 PM.
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Old 01-20-2015
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Just like spasemaster said,the following is meant and I also somehow found the language confusing,he explained it just perfectly but I am still adding some details :P

5'-- DNA DNA DNA-----Nucleotide X---3'(has an OH)

The Last Nucleotide has that free hydroxyl group at the 3' end,the incoming new nucleotide for DNA synthesis, 5' end of the new nucleotide will have that phosphate group see this picture,

The phosphate group will bind to the free 3' OH of the Nucleotide X and Dna chain elongation will take place...

5'-- DNA DNA DNA-----Nucleotide X(3'OH)--(5'Phosphate froup)New nucleotide

So somehow if we can block the 3' OH with some other group like azide..or something else then no new nucleotide will get that free 3' OH, The free OH is now changed to azide or something else so the Phosphate-OH linkage known as ester linkage will not occur any more so no more chain elongation

5'-- DNA DNA DNA-----Nucleotide X(3' no OH)

So 5' Phosphate cannot bind anymore chain synthesis blocked...

Look the 3' OH is modified here to N3,no more OH no more chain elongation

Hope this helped
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