Only one side of the DNA ladder is copied (the sense side). The sense side starts with a 3’ end. This means the corresponding mRNA will have to assemble starting from the 5’ end. This is my initial thought, but can someone expand on it? Also, is this explained by why replication is performed in the 5' to 3' direction as suggested by this thread: Why is DNA replication performed in the 5' to 3' direction?

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  • $\begingroup$ Is the DNA template strand the same as the DNA sense strand? $\endgroup$ – Cloud Dec 21 '13 at 1:35
  • $\begingroup$ No. Suppose your mRNA sequence from 5'to 3' is AGUC. Then, TEMPLATE strand is 3'-TCAG -5' but coding and sense strand is 5'AGTC3' i.e. complementary of the template strand and to the mRNA. This is a bit tricky so let someone else confirm this.... $\endgroup$ – biogirl Dec 21 '13 at 3:56
  • $\begingroup$ It seems as though the nomenclature for DNA sense and template strand can be same or differentiable as suggested by this: sci.sdsu.edu/~smaloy/MicrobialGenetics/topics/… $\endgroup$ – Cloud Dec 21 '13 at 4:31
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    $\begingroup$ The reason why the polymerization of DNA/RNA strands only happens in 5' -> 3' direction is because the polymerases can only add new nucleotides a the 3'OH-group of the existing strand linking it with the 5'-C of the next nucleotide. $\endgroup$ – Chris Dec 21 '13 at 10:17
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    $\begingroup$ The argument put forward at the link provided by @Cloud, that the DNA strand with the same sequence as the mRNA might be called the template strand because it is translated into a protein is illogical. The "template" referred to in the phrase "template strand" is the template for transcription - even the transcription of a sequence which will not encode a protein, rRNA for example, requires a template. $\endgroup$ – Alan Boyd Dec 21 '13 at 13:24

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