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Translation

Translation. AHMP 5406. Translation. Conversation of RNA info into protein RNA acts as the intermediate between DNA and protein Genetic code is key to translating RNA codons (3bp) into AA. Reading frame. An RNA sequence can be translated into 3 reading frames. tRNA structure.

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Translation

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  1. Translation AHMP 5406

  2. Translation • Conversation of RNA info into protein • RNA acts as the intermediate between DNA and protein • Genetic code is key to translating RNA codons (3bp) into AA

  3. Reading frame • An RNA sequence can be translated into 3 reading frames

  4. tRNA structure • Approx. 80 bp • Can bind to itself • Then folds into 3D structure • Unpaired sections from functional areas

  5. tRNA structure • SS 3’ end • Attachment for AA • Anticodon • Recognizes mRNA sequence • Other loops • D loop • T loop • Bases are sometimes modified • y – pseudouridine • D – dihydrouridine • Uracil derivatives

  6. Mature tRNAs • Must be modified before exiting nucleus • Synthesized as larger precursors • Some have introns • Used as quality control mechanism • Have modified bases • Facilitate conformation and codon recognition

  7. Aminoacyl-tRNA synthetases • Covalently attach AA to tRNAs • Usually different synthetases for each AA

  8. Energy required • ATP used to create high E molecule • Stored E used to tie AA together

  9. Controlling Accuracy of Synthetase Reaction • Specific AA has greatest affinity for its tRNA synth. • Size exclusion • Use of an editing site • Excludes correct AA

  10. Building Polypeptides • AA are added to C-terminal end of the polypeptide • Peptide bonds activated by covalent attachment to AA

  11. Ribosomes • Catalytic machinery decodes mRNA • Builds polypeptide • Made up of approx 50 different proteins and RNA • Ribozyme • Usually to major subunits • Small subunit ensures codon matching • Large subunit catalyses formation of peptide bonds

  12. RNA Binding Sites • 3 on the ribosome • Recognize tRNA • A = aminoacyl tRNA • P = peptidyl-tRNA • E = exit

  13. Process of Translation • Correct Aminoacyl-tRNA accepted by A site • Movement to P site releases first tRNA and creates peptide bond • tRNA binds to E site • Repeat of cycle ejects spend RNA • This process is slow

  14. Elongation factors • Increase efficiency and accuracy of translation • EF-Tu and EF-G in bacteria • EF-1 and EF2 in Eukaryotes • Hydrolyze GTP to GDP • Conformation changes coupled with Ribosome conformation changes

  15. EF-Tu/EF-1 • Produces two short delays before peptide bond formation • Which is irreversible • Allows time for incorrect aminoacyl-tRNA to dissociate • 99.9% accuracy for translation

  16. Initiation of Translation • Signaled by start codon (AUG) • Initiator tRNA carries AA methionine • Required to initiate translation • Eukaryotic initiation factors (eIFs) • Recognize 5’ cap • Only initiator tRNA can bind to small subunit

  17. Initiation of Translation • Poly A tail detected by eIF-4G through polyA binding proteins • Ensures transcript is complete

  18. Stop codons • End translation process • UUU, UAG or UGA • Do not specify AA • Release factors bind to stop codons • Proteins Similar in shape to tRNAs • Free C-terminal end of polypeptide

  19. Polyribosome • Many ribosomes can attach to one transcript

  20. Translational Control • Proteins bind to 5’ and 3’ UTRs • Negative translational control • Translational repressor

  21. Phosphorylation of Initiation factors • IFs needed initiate translation • Phosphorylation of eIF-2 will inactivate it

  22. mRNA stability • Destabilization • Shortening of Poly A tail • Cleaving of Poly A tail • Results in decapping

  23. Non-sense mediated Decay • Eliminates mRNAs with internal stop codons • If stop codon is detected downstream of all exon-exon boundaries • No decay • If stop codon is detected upstream of any exon-exon boundaries • mRNA decay occurs

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