Biochem 501: Part IV.9: Translation

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Biochem 501: Part IV.9: Translation
2013-12-06 16:10:11
Biochem 501 FINAL

Biochem 501 FINAL
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  1. What are genes
    Heritable traits, blueprints for synthesizing proteins
  2. Beadle and Tatum experiment
    • Metabolites A-->B-->C-->D, catalyzed by enzymes 1, 2, and 3.
    • Control cells: all three enzymes functional, cells grown on media with just A
    • Cells exposed to x-rays to create mutants
    • Mutant cells isolates, only grew on plates with C or D
    • Conclusion: Cells lacked enzyme 2 (and possibly 1), genes encode proteins
  3. Translation and transcription are both conducted:
    The same direction (3' to 5')
  4. Crick's adaptor hypothesis
    An adaptor translates nucleotide sequence into a polypeptide protein
  5. Nucleotide sequence is decoded with:
    • tRNAs
    •  -short (60-95), hihgly conserved, extensively modified, stable RNAs
    • Each type carries specific AA covalently attached to 3' OH end
    • 5' end of tRNA anticodon (corresponds to mRNA codon) can be more flexible in base pairing (wobble)
  6. tRNA structure
    Multiplely modified clover leaf
  7. Codon-anticodon base pairing impacts:
  8. Strong base pairs confer ___, while wobble base pair confers ____
    Coding specificity and coding flexibility
  9. Example of wobble base:
    • Inosine:
    • Can binds A, T, or C
  10. Properties of genetic code:
    • Triplet: 3 bases=1 amino acid
    • Redundant: Except Methionine and Tryptophan each AA coded for more than one codon. Codons that code same AA are synonymous
    • Universal: Same code used in all organisms
    • Biased: organisms preferentially use certain synonymous codes
  11. Initiation codon
    • Starts protein coding sequence
    • AUG
  12. Stop/Termination/Nonsense Codons
    • Do not code for anything
    • UAA, UAG, UGA
  13. Silent mutation
    • Changes mRNA sequence to a synonymous codon, no effect on resulting polypeptide
    • i.e. UUA to UUA (leu)
  14. Missense mutation
    • Change mRNA sequence from a codon for one AA to a codon for another, changing PP sequence
    • i.e. UUA (leu) to UCA (ser)
  15. Nonsense mutation
    • Change mRNA sequence from a codon for an AA to a stop codon. Terminates translation, results in truncated polypeptide
    • UUA (leu) to UAA (stop)
  16. Reading frame:
    Codon sequence that is translated into a PP
  17. Frame shift mutation
    • Disrupt normal reading frame:
    • Insert/delete in non-multiples of three
    • Entirely of PP downstream of FSM is changed
    • Usually results in aberrant stop codon
  18. Open reading frame (ORFs)
    • correlate with protein coding nucleotide sequence
    • A D-S DNA sequence has six potential reading frames (3 on each side)
    • Long reading frame without stop codons are ORFs, suggest a protein coding sequence
  19. Translational frameshifting results in:
    The production of two different proteins (intended, i.e gag and pol proteins)
  20. mRNA can be edited
    -enzyme mediated deamination changes nucleotide sequence
  21. There are ___ tRNAs than AAs
  22. Aminoacylation of tRNA by tRNA synthase
    • Amino acids---> loaded onto specific tRNAs by aminoacyl-tRNA synthase
    • Amino acid is activated by adenylation of carboxyl group
    • Aminoacyl-tRNA synthase (two classes, some with 2' OH initiating attack [class I, needs second step to add to 3'], some with 3'[type II]) then selects matching tRNA and "charges" it, transferring the amino acid to the tRNA 3' OH