Transcription

• Transcription is the process of making pre-mRNA using part of the DNA as a template

  • The DNA code is copied (transcribed) into a single strand of RNA called mRNA
• Stages of Transcription:

  1. The DNA helix unwinds to expose the bases to act as a template
  2. Only one chain of the DNA acts as a template
• Stages of Transcription:

  3. Like with DNA replication, this unwinding and unzipping is catalysed by DNA helicase

  4. DNA helicase breaks the hydrogen bonds between bases
• Stages of Transcription:

  5. Free mRNA nucleotides in the nucleus align opposite exposed complementary DNA bases

  6. The enzyme RNA polymerase bonds together the RNA nucleotides to create a new RNA polymer chain. One entire gene is copied
• Role of RNA polymerase:

  • Moves along the template strand and joins the nucleotides together to form a pre mRNA molecule
• Transcription:

  • A complementary mRNA copy of one gene on the DNA is created on the nucleus
  • mRNA is much shorter than DNA so it is able to carry the genetic code to the ribosome in the cytoplasm to enable the protein to be made
• Stages of Transcription:

  7. Once copied, the mRNA is modified (splicing) and then leaves the nucleus through the nuclear envelope pores
• In prokaryotes, transcription results directly in the production of mRNA from DNA
• In eukaryotes, transcription results in the production of pre-mRNA; this is then spliced to form mRNA