Why 5'->3' and not 3'->5' ?

Jeffrey A. Cohlberg cohlberg at csulb.edu
Tue Mar 31 16:44:48 EST 1998

Someone wrote:
> Yes, but why is the triphosphate group not off the 3' end? :)
> You evolutionist continually ignore the obvious design.

It may be relevant that nucleoside-3'-phosphates exist in solution as an 
equilibrium mixture of 2' and 3' isomers.  They interconvert through a 
nucleophilic attack of the free hydroxyl on the phosphorus atom, with 
the other hydroxyl as a leaving group.  Nucleoside-3'-triphosphates, if 
they existed, would undergo the same type of isomerization.  On the 
other hand, a nucleoside-5'-phosphate (or triphosphate) does not undergo 
this sort of isomerization.  One could argue that this fixed structure 
would be better suited to be a precursor for evolution of nucleic acids.
Jeffrey A. Cohlberg, Professor
Department of Chemistry and Biochemistry
California State University, Long Beach
1250 Bellflower Blvd.
Long Beach, CA 90840
phone (562) 985-4944	fax (562) 985-8557

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