In article <6fes6c$jqt at ringer.cs.utsa.edu>, jkumar at lonestar.jpl.utsa.edu
(Jay . Kumar) wrote:
Quick answer:
Because the triphosphate group is off the 5' and not the 3'
Long answer:
The lose of the pyrophosphate group supplies the energy for the
phosphodiester bond formation (over simplification, but P-Chem isn't my
strong suit). If the NA builds 3' -> 5', the growing chain supplies the
energy group, not the incoming nucleotide. This means if an incorrect base
is inserted, a proof-reading enzyme would excise the last base and its
triphosphate group. Before it could proceed with the correct base, it
would have to put a pyrophosphate group back on, which would require a loss
of energy from somewhere else. 5' -> 3' removes the mismatch and begins
elongating with the next (d)NTP.
--
Scott McMahan
mcmahan at oncology.wisc.edu
