transcription of dna to rna

• what is transcription?

  
  

  transcription is the first step in the gene expression

  it involves the production of a complementary RNA molecule from a dna template
• what happens in stage 1 -initiation

  transcription starts at a specific location in the dna called the promoter

  an enyzme called RNA polymerase binds to the promoter

  the double helix unwinds exposing the template strand that will guide RNA synthesis
• what happens in stage 2 - elongation

  RNA polymerase uses nucleotide triphosphates as substrates to replicate the dna sequences

  it synthesises the new RNA strand in the 5' to 3' direction

  the dna that has been transcribed rewinds into a double helix
• what happens in stage 3 termination

  once a gene is completely transcribed, the process of transcription ends

  the RNA transcript a mirrored copy of the original DNA sequence is complete

  the RNA molecule then detaches from the dna
• post transcription modification in eukaryotes

  this process only occurs in eukaryotic cells

  newly transcribed RNA known as primary transcript or pre mRNA undergoes modification to become mRNA

  A 5' cap and poly A tail are added for protection and transport out of the nucleus
• what are introns

  are non coding sequences that are removed
• what are exons

  the coding sequences are spliced together
• what is transcription

  enables the cell to produce the specific proteins it needs to function

  variations in the transcription process can lead to gene expression changes which can affect an organisms characteristics