[travellingsalesman]

Have you ever wondered as to why does 3'-5' strand acts as the template and not 5'-3' strand?

Looking forward to your answers. I am actually looking forward to the best answer (one which is amazingly explained, so that anyone can understand the reason without much a do).

P.S. I'm thinking of awarding the author of best answer (in my own personal judgement) with a little award (A book titled "Science Lessons: What the business of biotech taught me about management", by Gordon Binder (former CEO of Amgen Inc)...this book is amongst Top 10 best books to read in Biotechnology field...so I hope who so ever wins, will love this little present from me...I am doing this personal contest sort of activity first time ever on this forum, if it turns out nice, will post more of these mini contests in future (as and when my wallet has some extra bucks to go for these activities  ).

Looking forward..

Chemically/Energitically -

Nucleic acid polymerization - Transcription/Replication is a SN2 nucleophilic reaction. 3'OH  oxygen is a good attacking group and so the leaving group(pyrophosphate - also very good leaving group) does not require additional energy source(ATP) for the removal oxygen. 

This energetic constraint leads to
evolutionary Selectivity-

i.e - Protein synthesis(Translation), also occurs from 5' - 3'.(Ref 1 - Rna Based evolution)
Ref -1
http://fire.biol.wwu.edu/cmoyer/zztemp_f...rld_02.pdf

So the regulatory/initiation sequences(Eg - Shine-Dalgarano Sequence) also lie on 5' end of the transcript. 

In addition other machinery(repair) also evolved in a similar fashion. (Ref 2)They show that organisms with 5' - 3' polymerase  activity have better survival rates(mutations - Repair machinery require 5'-3' activity).
Ref -2
http://journals.plos.org/plosone/article...ne.0018881.


BTW - 3'-5' synthesis is also possible both, in vivo/in vitro - Thg1 superfamily proteins(Ref -3).

Ref - 3
https://www.ncbi.nlm.nih.gov/pubmed/22456265
Ref - 4
http://onlinelibrary.wiley.com/doi/10.10...201203859/