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RNA Polymerase Direction

  1. Mar 25, 2016 #1
    If RNA polymerase moves from the 3' to 5' end of the template strand to synthesize an mRNA strand from the 5' to 3' end (http://www.ncbi.nlm.nih.gov/books/NBK22085/), how come promoters are located on the 5' end (said in my Biology class)?

    It was also mentioned that while RNA polymerase moves 3' to 5', the DNA itself is read 5' to 3'. Is that referring to the sense strand?
     
  2. jcsd
  3. Mar 25, 2016 #2
    DNA is a double helix, so a promoter region at the 5' end has a corresponding promoter region at the 3' end. For example, the promoter nucleotide sequence at the 5' end is TATAAAA, which will have a corresponding nucleotide sequence of ATATTTT, which will be at the 3' end of the other strand of DNA.

    The DNA strand with the promoter box on the 3' end will be the template strand which will be translated into RNA by RNA polymerase.

    Not entirely sure what you mean on your last point. The RNA polymerase transcribes the 3' to 5' strand into corresponding RNA nucleotides, so it's effectively creating a copy of the 5' to 3' strand of DNA (but remember RNA has uracil instead of thymine).
     
  4. Mar 25, 2016 #3

    Ygggdrasil

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    The confusion comes from the two different strands of DNA. RNA polymerase moves from the 3' to 5' of the template strand, producing an mRNA that is complementary to the template. The other strand of DNA that the polymerase does not read is called the non-template strand. Because the non-template strand is also complementary to the template strand, the mRNA ends up having the same sequence as the non-template strand (except that T is replaced with U). Therefore, we often refer to the non-template strand as the coding or sense strand.

    When we look at genes, we usually think of the gene as the sequence on the coding strand. From this perspective, the promoter is upstream (at the 5' end) of the coding sequence.
     
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