Gene transcription

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When a gene is copied from its DNA form to its RNA form[1]. The antisense strand of DNA acts as a template strand and is used by RNA polymerases to synthesise mRNA . In eukaryotes, the mRNA produced in transcription is modified through the addition of a  polyA tail and 5' cap. The modified mRNA can then be used in translation at the ribosomes by tRNA to synthesise a polypeptide, allowing the gene to be expressed[2]

The process of transcription involves three major stages: initiation, elongation and termination. During initiation, RNA polymerase enzyme binds to the promotor sequence upstream of the gene on the antisense strand, this is the closed complex. Binding of the RNA polymerase to the promoter causes local denaturation of the DNA so it starts to unwind, this is known as the open complex. The next stage of transcription is elongation where the strand of mRNA is synthesised. RNA polymerase synthesises mRNA using RNA nucleotides and the principles of complementary base pairing, meaning that the mRNA synthesised is identical to the sense strand but with uracil instead of thymine. Transcription stops when the RNA polymerase enzyme reaches a terminator sequence, the mRNA then detaches from the DNA[3]


Three stages of transcription: Initiation, elongation and termination


References

  1. https://en.wikipedia.org/wiki/Transcription_(biology)
  2. Khan Academy. Overview of transcription: in transcription, the DNA sequence of a gene is transcribed (copied out) to make an RNA molecule. Date published unknown [Accessed 5/12/18]; Available from: https://www.khanacademy.org/science/biology/gene-expression-central-dogma/transcription-of-dna-into-rna/a/overview-of-transcription
  3. Bozeman Science. Steps of Genetic Transcription. Date published unknown [Accessed 5/12/18]; Available from: https://courses.lumenlearning.com/wm-biology1/chapter/reading-steps-of-genetic-transcription/
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