Protein synthesis

• What are the two stages of protein synthesis?

  Transcription and translation.
• what is transcription?


  Complementary mRNA copy of one gene on the DNA is created in the nucleus. mRNA is much shorter than DNA so is able to Cary the genetic code to the ribosome in the cytoplasm to enable the protein to be made.
• Stages of transcription?


  1 dna helix unwinds

  2 one chain of the DNA acts as a template

  3 unwinding/ unzipping is catalysed by the DNA helicase

  4 DNA helicase breaks the hydrogen bonds between bases

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

  6 RNA polymerase bonds the RNA nucleotides to create a new RNA polymer chain. One entire gene is copied.

  7 once copied the mRNA is modified and then leaves the nucleus through the nuclear envelope pores
• What’s pre mRNA?


  It has to be modified to become mRNA that is ready to leave the nucleus and take part in translatio. Introns are spliced out by a protein called splicesome. This leaves just the exons in the coding regions. Finished mRNA is made up of just exons.
• transcription


  1 gene on the DNA is copied into mRNA inside nucleus
• Translation


  mRNA joins with a ribosome and corresponding tRNA molecules brings the specific amino acid the codon codes for
• What is translation?


  Polypeptide chain is created using both the mRNA base sequence and the tRNA
• Stages of translation


  1. Modified RNA leaves the nucleus and attaches to a ribosome

  2. Ribosome attaches to start codon

  3. tRNA molecule with the complementary anticodon aligns opposite the mRNA

  4. Ribosome moves across the mRNA molecule meaning complementary tRNA attaches to the next codon

  5. 2 amino acids that were delivered by the tRNA molecule are joined by a peptide bond- catalysed by enzyme and requires ATP

  6. Continues until ribosome reaches stop codon at end of mRNA molecule. Ribosome detach(stop codon doesn't code)

  7. Polypeptide chain is now created and will enter Golgi body for folding and modification