Protein Synthesis

• Transcription is when one gene on DNA is copied to mRNA.
• Translation is when mRNA joins to a ribosome in cytoplasm, tRNA molecules brings the specific amino acid to the codon it codes for.
• Transcription


  1 - DNA helix unwinds to expose the bases to act as a template (only one strand acts as the template). Unwinding and unzipping catalysed by DNA helicase (breaks hydrogen bonds between bases).

  2 - Enzyme RNA polymerase bonds the RNA nucleotides to create a new RNA polymerase chain. One entire gene is copied, modified, and then leaves the nucleus through nuclear envelope pores.
• Pre-mRNA is mRNA before it is modified and before it leaves the nucleus. Introns are then spliced out by splicesome (protein) to form mRNA.
• Translation


  1 - modified mRNA leaves the nucleus and attaches to a ribosome in the cytoplasm which then attaches to the start codon.

  2 - tRNA with complementary anticodon to start codon aligns opposite mRNA (held in place by ribosome)

  3 - ribosome moves along mRNA molecule to allow other complementary tRNA to attach to the next codon on the mRNA.

  4 - two amino acids delivered by tRNA joined together by peptide bond (catalysed by an enzyme released by ribosome and requires ATP)

  5 - Continues until stop codon is reached which does not code for an amino acid so ribosome detaches.