BMSC 220 Topic 7

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  1. Translation
    • -carried out on ribosomes with tRNA's serving as adaptors between mRNA template and AA being incorporated into protein
    • -each AA coded for by a triplet of nucleotide sequence in mRNA
  2. First AA Always Coded for in Translation
    • -always Methionine
    • -AUG codon
  3. Codons
    • -61 possible codons
    • -each codon is for specific AA or stop sequence 
    • -AA can have more than one codon for it
    • -3 stop codons
    • -always codes AUG for methionine at the start
  4. Aminoacyl tRNA
    -tRNA with a specific AA covalently bound at 3' end
  5. Image Upload 1
    • Image Upload 2
    • -green part is aminoacyl tRNA
    • -red UAC is anticodon
  6. rRNA
    • -ribosomal RNA
    • -form the components of ribosomes 
    • -can be up to 10,000,000 (25% of dry weight)
  7. Prokaryotic 70S Ribosome
    • -50S large sub unit
    • -30S small sub unit
  8. Eukaryotic 80S Ribosome
    • -60S large subunit 
    • -40S small subunit
  9. Ribosome Assembly
    • -assembled in nucleolus of the nucleus 
    • -ribosomal proteins are imported to the nucleus and attach to pre-rRNA. the pre-rRNA splits in two, one part the 40S the other the 60S subunit
  10. tRNA
    • -synthesized by RNA polymerase III
    • -possess unique 3 nucleotide sequences(anticodon) that pair the tRNA with the specified AA
    • -70-80 nucleotides long and have characteristic cloverleaf structures based on intramolecular base pairing
  11. Location of Anticodon on tRNA
    -anticodon is on opposite side of molecule from actual AA binding site
  12. How Many Different Aminoacyl tRNA Synthetases are there?
    • -20
    • -each one recognizes the correct AA
    • -the correct codon on the mRNA
  13. Steps to Attaching AA to tRNA
    • -AA is activated
    • -AA is added to tRNA
    • -error rate is about 1/1000
  14. Cistron
    • -classical term for the smallest genetic unit for a specific trait
    • -essentially the same as a gene in today's context
  15. Prokaryotic mRNA is _cistronic
    Eukaryotic mRNA is _cistronic
    • -polycistronic
    • -monocistronic
  16. 3 Stages of Translation
    • -initiation
    • -elongation
    • -termination
  17. RF
    -releasing factor
  18. EF
    -elongation factor
  19. IF
    -initiation factor
  20. Translation Initiation in Prokaryotes
    -look for a specific nucleotide sequence, Shine-Dalgarno sequence
  21. Translation Initiation in Eukaryotes (step 1)
    • -40S subunit, various initiation factors (eIFs) and charged tRNA(charged with methionine) assemble
    • -tRNA with methionine always binds to 40S subunit before the subunit binds to mRNA
  22. Translation Initiation in Eukaryotes (step 2)
    -40S, tRNAmet, eIF complex meets up with mature mRNA and binds to the 5' m7G cap
  23. Translation Initiation in Eukaryotes (step 3)
    • -entire complex sitting at the 5' end of mRNA slides along mRNA until it finds the start AUG codon
    • -requires ATP for scanning procedure
  24. Translation Initiation in Eukaryotes (step 4)
    • -complex disassembles (tRNAmet and 40S stay on mRNA) initiation factors leave
    • -60S subunit binds
  25. tRNA Binding Sites in Ribosome
    • -aminoacyl-A site-tRNA arrival site
    • -peptidyl-P site-polypeptide (pause) site
    • -exit-E site-tRNA leaves ribosome
  26. Role of Elongation Factors in Elongation
    -EF are complexed to GTP's and escort aminoacyl tRNA to the ribosome (A site)
  27. Decoding Center
    • -within 40S subunit ensures proper aminoacyl tRNA pairs with the codon
    • -third step in specificity (after AA-tRNA pairing and simple base pairing)
  28. Translation Elongation (step 1)
    • -tRNAmet sits in AUG start
    • Image Upload 3
  29. Translation Elongation (step 2)
    • -next tRNA comes to A 
    • Image Upload 4
  30. Translation Elongation (step 3)
    • -peptide bond formation between first two AA
    • -AA chain is transferred from P site tRNA to A site tRNA
    • Image Upload 5
  31. Translation Elongation (step 4)
    • -ribosome moves downstream (tRNA moves from A site to P site=translocation)
    • -A site is ready for next charged tRNA
    • -energy dependent process(GTP)
    • Image Upload 6
  32. Translation Termination (step 1)
    -stop signal on the mRNA arrives in A site
  33. Translation Termination (step 2 and 3)
    • -step 2-releasing factor (purple blob) sits in A site at UAA codon (3 stop codons possible)
    • -step 3-polypeptide chain is released
    • Image Upload 7
  34. Translation Termination (step 4)
    -release factor causes structure to come apart (ribosomal subunits can be reused)
  35. Protein Cleavage
    • -some proteins must be cleaved to become an active protein
    • -ex. insulin
  36. Post Translational Modification
    -chemical modification of a polypeptide chain after translation
  37. Phosphorylation
    • -method of post translation modification
    • -phosphate addition on serine, threonine or tyrosines by protein kinases 
    • -phosphotases act to reverse phosphorylation
  38. Glycosylation
    • -method of post translation modification
    • -carbohydrate addition to protein to form glycoprotein
  39. Lipid Addition
    • -method of post translation modification
    • -lipid addition to form lipoprotein
  40. Regulation of Protein Levels in a Cell
    • -controlled at level of transcription and translation, which determines the amount of protein/enzyme that is made by the cell
    • -also controls how quickly a protein is degraded
  41. Ubiquitin
    -marker in eukaryotic cells that targets cytosolic and nuclear proteins for rapid proteolysis(degradation)
  42. Proteasomes
    -large, multi subunit protease complexes that recognize and degrade polyubiquinated proteins
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BMSC 220 Topic 7
BMSC 220 Topic 7
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