Chapter 15: Protein Synthesis

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Chapter 15: Protein Synthesis

Protein synthesis is carried out in three distinct stages: transcription; translation; and protein folding

1. Transcription

  • Enzymes unwind the double helix and separate the two strands by breaking the hydrogen bonds between the bases where the gene is located
  • RNA polymerase synthesises messenger RNA (mRNA) using one of the strands of DNA as a template
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2. Translation

  • mRNA moves to cytoplasm and combines with a ribosome made up of two ribosomal RNA (rRNA) subunits
  • Each 3-base (triplet) sequence of the mRNA is a codon that specifies either a start codon, a particular amino acid, or a stop codon
  • Transfer RNA (tRNA) is another type of RNA – it is found free-floating in the cytoplasm and is responsible for carrying one amino acid. (Remember amino acids are the building blocks of proteins)
  • tRNA has a 3-base (triplet) sequence called the anti-codon that is complementary to a particular codon on the mRNA
  • Each tRNA in turn (with its own amino acid) lines up with the mRNA in the ribosome and an amino acids are joined together in a long polypeptide line which will form the protein
  • This process continues until the stop codon on the mRNA is reached at which point all the translation machinery separates and the protein is released and it folds up into its active form and goes and carries out its specific function
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3. Protein Folding

  • The chain of amino acids leaves the ribosome and is sent to specific areas of the cell where it is packaged into its functional shape