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Translation

translation - begins when mRNA binds to rRNA 

  • tRNA w/ complementary 3-nucleotide sequence (anticodon)
  • 45 different tRNA molecules (some tRNA recognize more than 1 codon)
  • activating enzymes - pairs 3-nucleotide sequences w/ amino acids
    • aminoacyl-tRNA synthetase - 1 exists for each of 20 common proteins, attaches tRNA to amino acids
    • corresponds to an amino acid and 1-6 different anticodons
  • nonsense codons - UAA, UAG, UGA
    • has no complementary anticodon
    • used as “stop signals
  • methionine - AUG, “start” signal
  • initiation - begins w/ initiation complex formation
    • initiation factors - proteins that position tRNAfMet(in prokaryotes) or methionine (in eukaryotes) at P site, where peptide bonds form
    • A (aminoacyl) site - where successive amino-acid-bearing tRNA will bind
    • E (exit) site - where empty tRNA exit ribosome
    • positioning of mRNA determines reading frame
    • leader sequence - marks beginning of each mRNA
    • prokaryotes include several genes on a single mRNA (polycistronic mRNA)
    • eukaryotes include 1 gene per mRNA (monocistronic mRNA)
  • elongation - elongation factor proteins bind tRNA to mRNA at A site
    • ribosome catalyzes reaction that removes amino acid from tRNA and creates peptide bond w/ next amino acid
  • translocation - ribosome moves amino acids out, through E site
  • termination - nonsense codons recognized by release factors (proteins that release polypeptides from ribosome)
Subject: 
Biology
Subject X2: 
Biology

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