DNA polymerase direction

[sagda]

Why do DNA polymerases elongate chains in the 5' to 3' direction only ? why not from 3' to 5' ?

[mith]

try drawing out the elongation process. remember to count the phosphates.

[JackBean]

Try to think about repairing mistakes in both cases

[MrMistery]

jackbean is right: conceptually it could go the other way, but repair... that's a different story

[sagda]

I tried to draw it, the 3'-oH of the incoming nucleotide will be added to the primer terminus ( which has a 5'-triphosphate ), then removal of the incorrect 5' terminal triphosphate takes place, and the primer becomes 5' monophosphate....why don't the DNA polymerase continue elongation after that? is this a necessary condition( primer must be triphosphate) for elongation to take place?

[JackBean]

You need to release energy in order to add new nucleotide. So, if you had there monophosphate, you have nothing to hydrolyse and thus you can't add new nucleotide