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Translation. Chapter 9. Overview. Occurs on ribosomes-large aggregates of rRNA and protein tRNA acts as amino acid carriers Prokaryotes—occurs simultaneously with transcription and mRNA degradation Eukaryotes—occurs in cytoplasm mRNA translated 5’ 3’ Protein synthesis aminocarboxy.

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translation

Translation

Chapter 9

overview
Overview
  • Occurs on ribosomes-large aggregates of rRNA and protein
  • tRNA acts as amino acid carriers
  • Prokaryotes—occurs simultaneously with transcription and mRNA degradation
  • Eukaryotes—occurs in cytoplasm
  • mRNA translated 5’3’
  • Protein synthesis aminocarboxy
protein synthesis
Protein Synthesis
  • Polymerization of amino acids: condensation reaction (dehydration synthesis)
universal genetic code
~Universal Genetic Code
  • Codons—sets of 3 nucleotides corresponding to a single amino acid
  • Each codon specifies a single amino acid
  • More than one codon can specify the same amino acid
  • code is said to be degenerate
  • Some aa correspond to a single codon
    • AUG—initiator codon, methionine (Met, M)
    • UGG–Tryoptophan (TrP, W)
  • Often codons encoding the same aa differ onl;y at the 3rd nucleotide
why universal exceptions

NH3+

H-C-CH2SeH

COO-

Why~Universal? Exceptions
  • GUG sometimes used as a start
  • Mammalian mitochondria
  • Ciliated protozoa
  • Selenocysteine
selenocysteine
Selenocysteine
  • The 21st amino acid?
  • An essential amino acid for selenoproteins EX. Glutathione oxidase
  • Uses unique tRNA, initially bound to Ser
  • Anticodon recognizes UGA (Stop) as Sec
  • Signals in 3’ region determine Stop or Sec
  • Dedicated specific elongation factor
degeneracy wobble hypothesis
Degeneracy—Wobble Hypothesis
  • Explains how some tRNA recognize more than one codons
  • tRNA molecules only need to make strong base pairs with 2 of the three codons in the nucleotide
  • This third loose base pairing interaction is called wobble
  • Note: only certain bases can substitute for others
wobble example
Wobble Example

This UCA codon was read by the

tRNA with a UGA anticodon

But if this UCA was UCG, it would still have been read by the tRNA with a UGA anticodon

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