Protein Synthesis

Key points of the process of protein synthesis- transcription and translation

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  • DNA helicase acts on specific region of DNA molecule- breaks hydrogen bonds between bases forming 2 exposed DNA strands
  • RNA polymerase (activated by transcription factors) moves along template strand causing nucleotides on this strand to join with complementary nucleotides
  • Uracil replaces thymine
  • Nucleotides added one at a time to form pre- mRNA strand (complementary to DNA strand, condensation reactions)
  • DNA strands rejoin
  • when RNA polymerase reaches stop code it detaches and pre-mRNA strand produced.
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Splicing pre-mRNA

  • Forms mRNA
  • Introns (non coding regions) of mRNA removed (present as copied from DNA)
  • Exons are rejoined
  • mRNA can now pass out of the nucleus through a nuclear pore
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  • Ribosome attached to starting codon at one end of mRNA
  • tRNA molecule with complementary anticodon sequence moves to ribosome and pairs up with mRNA sequence
  • tRNA carries a specific amino acid
  • Complementary anticodon of tRNA pairs up with next codon on mRNA...
  • Ribosome moves along mRNA...
  • Amino acids are joined by peptide bonds through enzyme and ATP
  • Ribosome holds  2 tRNA molecules at a time
  • tRNA diffuses away
  • Process is repeated till stop codon of mRNA is reached
  • Polypeptide chain built up
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Post Translational Modifications

  • Polypeptide chain assembled into protein
  • Coiled or folded: Secondary
  • Further folded: Tertiary
  • Different ones linked: Quarternary
  • Proteins altered before becoming functional
  • Modifications carried out by enzymes: include chain cutting, adding methyl or phosphate groups to amino acids, adding sugars or lipids
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