8.4. Transcription and Splicing

• 1. A section of DNA is copied into mRNA. This section is often a gene that codes for a protein
• 2. Transcription takes place in the nucleus of a eukaryotic cell.

  3. RNA polymerase attaches to a section of DNA. Associated with DNA helicase in breaking the hydrogen bonds between two strands.
• 4. DNA unwinds exposing bases. One of the strands is used as a "template" strand.

  5. An mRNA strand is synthesised, free RNA bases are attracted to the exposed pairs. Forming hydrogen bonds
• 6. RNA polymerase catalyses the formation of phosphodiester bonds between the RNA molecules, creating a new strand of mRNA.

  7. The double helix then reassembles and mRNA leaves through the nuclear pores.

  The mRNA then leaves to go off to associate with a ribosome.
• Introns are removed from the pre-mRNA, and exons are spliced together.
• Once spliced, the mRNA is then mature. Splicing does not occur in prokaryotes because translation occurs immediately
• Translation occurs almost immediately in prokaryotes because they do not have non-coding introns
• Antisense: Non coding strands
• Sense strand: Coding