Transcription (HL)

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•  Transcription occurs in a 5’ to 3’ direction

Transcription is the process by which a DNA sequence (gene) is copied into a complementary RNA sequence by RNA polymerase

  • Free nucleotides exist in the cell as nucleoside triphosphates (NTPs), which line up opposite their complementary base partner
  • RNA polymerase covalently binds the NTPs together in a reaction that involves the release of the two additional phosphates
  • The 5’-phosphate is linked to the 3’-end of the growing mRNA strand, hence transcription occurs in a 5’ → 3’ direction

Direction of Transcription

Overview of Transcription

The process of transcription can be divided into three main steps: initiation, elongation and termination

  • In initiation, RNA polymerase binds to the promoter and causes the unwinding and separating of the DNA strands
  • Elongation occurs as the RNA polymerase moves along the coding sequence, synthesising RNA in a 5’ → 3’ direction
  • When RNA polymerase reaches the terminator, both the enzyme and nascent RNA strand detach and the DNA rewinds

Many RNA polymerase enzymes can transcribe a DNA sequence sequentially, producing a large number of transcripts 

  • In eukaryotes, post-transcriptional modification of the RNA sequence is necessary to form mature mRNA

Summary of Transcription

transcription summary

Transcription Animation