Genetic Code & Cell Function

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  • Genetic Code & Cell Function
    • Protein Synthesis
      • Transcription
        • 1. DNA helicase acts on a specific region of the DNA molecule
          • It breaks the hydrogen bonds between DNA bases
          • Strands unzip and unwind to expose the nucleotide bases
        • 2. RNA polymerase links to the DNA template strand (about to be transcribed)
          • RNA polymerase catalyses the free RNA nucleotides to the template strand
            • Complimentary base pairing
        • 3. RNA polymerase moves along DNA to form bonds between the RNA nucleotides
          • Free RNA nucleotides attach to the chain to produce mRNA (alongside the unzipped piece of DNA)
          • Behind RNA polymerase the DNA strands rewinds and returns to a double helix
        • 4. RNA polymerase separates when it reaches a 'stop' codon
          • mRNA production is now complete
        • 5. mRNA carries DNA code out of the nucleus, through the nucear pores and into the cytoplasm
          • This is where the mRNA attaches itself to a ribosome
      • Translation
        • Translating codons on mRNA into a sequence of amino acids to a polypetide
        • 1. Ribosome becomes attached to the 'start' codon at one end of the mRNA molecule
        • 2. 1st tRNA with anticodon complimentary to the first codon on the mRNA attaches itself to the ribosome
          • A second tRNA with the second anticodon complimentary to the second codon of the mRNA molecule attaches itself to the ribosome etc.
        • 3. The two amino acids on the tRNA molecules are close enough to form a peptide bond
          • 1st tRNA leaves the ribosome which leaves an attachment site vacant
          • Ribosome now moves one codon along the mRNA strand
        • 4. Polypeptide 'grows' a an attachment becomes vacant it is occupied by another tRNA with a complimentary anticodon to the codon of the mRNA.
          • As the ribosome moves along the mRNA a polypeptide forms
        • 5. There may be several ribosomes on a single mRNA
          • Each one reading from the coded information at the same time
            • Polysome system
              • Many polypeptides form


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