Editing Transcription (biology) (section)

== Background ==
A DNA transcription unit encoding for a protein may contain both a ''coding sequence'', which will be translated into the protein, and ''regulatory sequences'', which direct and regulate the synthesis of that protein. The regulatory sequence before ([[Upstream and downstream (DNA)|upstream]] from) the coding sequence is called the [[five prime untranslated region]]s (5'UTR); the sequence after ([[Upstream and downstream (DNA)|downstream]] from) the coding sequence is called the [[three prime untranslated region]]s (3'UTR).<ref name="Biology">Eldra P. Solomon, Linda R. Berg, Diana W. Martin. ''Biology, 8th Edition, International Student Edition''. Thomson Brooks/Cole. {{ISBN|978-0495317142}}</ref>

As opposed to [[DNA replication]], transcription results in an RNA complement that includes the nucleotide [[uracil]] (U) in all instances where [[thymine]] (T) would have occurred in a DNA complement.<ref name="Clark-2005">{{Cite book |last=Clark |first=David P. |url=https://books.google.com/books?id=9Hw-mstILcIC |title=Molecular Biology |date=2005-06-24 |publisher=[[Elsevier]] |isbn=978-0-08-045421-4 |pages=134 |language=en}}</ref>

Only one of the two DNA strands serves as a template for transcription. The [[Sense (molecular biology)|antisense]] strand of DNA is read by RNA polymerase from the 3' end to the 5' end during transcription (3' → 5'). The complementary RNA is created in the opposite direction, in the 5' → 3' direction, matching the sequence of the sense strand except switching uracil for thymine. This directionality is because RNA polymerase can only add nucleotides to the 3' end of the growing mRNA chain. This use of only the 3' → 5' DNA strand eliminates the need for the [[Okazaki fragment]]s that are seen in DNA replication.<ref name="Biology" /> This also removes the need for an [[Primer (molecular biology)|RNA primer]] to initiate RNA synthesis, as is the case in DNA replication.

The ''non''-template (sense) strand of DNA is called the [[coding strand]], because its sequence is the same as the newly created RNA transcript (except for the substitution of uracil for thymine). This is the strand that is used by convention when presenting a DNA sequence.<ref>{{cite web|url=http://www.sci.sdsu.edu/~smaloy/MicrobialGenetics/topics/chroms-genes-prots/temp-strand.html|title=DNA Strands|website=www.sci.sdsu.edu|access-date=1 May 2018|url-status=live|archive-url=https://web.archive.org/web/20171027100724/http://www.sci.sdsu.edu/~smaloy/MicrobialGenetics/topics/chroms-genes-prots/temp-strand.html|archive-date=27 October 2017}}</ref>

Transcription has some proofreading mechanisms, but they are fewer and less effective than the controls for copying DNA. As a result, transcription has a lower copying fidelity than DNA replication.<ref name="Stryer_2006">{{cite book |vauthors=Berg J, Tymoczko JL, Stryer L | title=Biochemistry | publisher=W. H. Freeman | edition=6th | location=San Francisco | year=2006 | isbn=0-7167-8724-5 }}</ref> <!-- page 788 in 5th edition -->