L18-Translation - Translation Topics The Genetic Code tRNA...

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Unformatted text preview: Translation Topics The Genetic Code tRNA and rRNA roles Catalytic RNA Ribosome Structure and Function Translational Initiation, Elongation and Termination Protein Folding & PostTranslational Modification Antibiotics and the Inhibition of Translation 1 The Important (Exam) Stuff Explain the genetic code (codons and anticodons). Describe the function(s) of each type of RNA in protein translation. Explain each stage of protein synthesis (initiation, elongation and termination). Describe posttranslational protein changes. Explain how specific antibiotics inhibit specific stages of protein translation. The Central Dogma (Again) 2 RNA (again) = Protein Synthesis The Software: Messenger RNA 3 The Genetic Code CODONS 1 start 3 stop 61 a.a. (including start) F met bacterial start CODONS Degenerate (forgiving) st 1 2 bases more important rd than 3 base Specific Codons Translate into Specific Amino Acids Mutations changing nucleic acid sequence can cascade down and create changes in amino acid sequences often yielding different protein conformation. 4 Transfer RNA aminoacyl tRNA synthase mRNA codon rRNA + protein = ribosome Svedberg Unit (S): A unit of centrifugation sedimentation rate. 20 nm 70S Holoenzyme 30S subunit (small) 50S subunit (large) 16S rRNA 21 polypeptides 5S + 23S rRNA 34 polypeptides 5 Ribozymes Riboswitches Catalytically active RNA molecules. Present in bacteria, archaea & eukarya. Rnase P found in microbes catalyzes tRNA "trimming". Riboswitch glmS regulates transcription of gram+ cell wall component synthesis gene. The micF antisense RNA gene regulates gram outer membrane porin expression. Ribosomal RNAs catalyze all mRNA and tRNA translocation, peptide bond formation, etc. Ribosomes synthesize protein Translational Domain 6 50S Elongation f f 7 f f Termination 8 Translation: The Movie Polysomes Ribosomes can be present every 80 bases on a bacterial mRNA. Bacterial transcription is simultaneous with translation 9 Some bacterial proteins are secreted. Some remain inside the cell. Signal sequence is often cleaved after secretion Chaperonins keep proteins from folding until after they are secreted Posttranslational modification 10 Antibiotics interrupt Translation Initiation -- Initiation Complex Formation sensitive to aminoglycosides Prevents binding of fMET tRNA bacteriocidal Example: streptomycin tRNA binding to A site Sensitive to cyclines Affects small (30S) subunit bacteriocidal Example: tetracycline tRNAbinding to Asite Antibiotics interrupt Translation Peptidyl transferase Peptide Transfer Peptidyl transferase Sensitive to chloramphenicol Prevents peptide bond Bacteriostatic Psite Transfer Transfer to Psite Translocation Sensitive to erthyromycin Prevents A to P transfer Bacteriostatic 11 Text References th Pages 193204 (11 Edition) 12 ...
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