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TAMU BIOL 111 - Ch17_GeneExpression

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Chapter 17Slide 2Slide 3Slide 4Cracking the CodeSlide 6Synthesis of an RNA TranscriptRNA Polymerase Binding and Initiation of TranscriptionElongation of the RNA StrandAlteration of mRNA EndsSplit Genes and RNA SplicingTranslationThe Structure and Function of Transfer RNARibosomesSlide 15Slide 16Ribosome Association and Initiation of TranslationElongation of the Polypeptide ChainTermination of TranslationPolyribosomesMutationsSubstitutionsInsertions and DeletionsSummary of Transcription and TranslationYou should now be able to:Slide 26PowerPoint Lectures for Biology, Eighth EditionNeil Campbell and Jane ReeceChapter 17Chapter 17From Gene to Protein•The ribosome–Is part of the cellular machinery for translation, polypeptide synthesisFigure 17.1•In prokaryotes–Transcription and translation occur togetherFigure 17.3a(a)TRANSLATIONTRANSCRIPTIONDNAmRNARibosomePolypeptide•In eukaryotes–RNA transcripts are modified before becoming true mRNATRANSCRIPTIONRNA PROCESSINGTRANSLATIONmRNADNAPre-mRNAPolypeptideRibosomeNuclearenvelopeFigure 17.3b•During transcription–The gene determines the sequence of bases along the length of an mRNA moleculeFigure 17.4DNAmoleculeGene 1Gene 2Gene 3DNA strand(template)TRANSCRIPTIONmRNAProteinTRANSLATIONAmino acidA C CA A A C C G A GTU G GUU UGG CU CATrpPheGlySerCodon3535Cracking the Code•A codon in messenger RNA–Is either translated into an amino acid or serves as a translational stop signalFigure 17.5Second mRNA baseU C AGUCAGUUUUUCUUAUUGCUUCUCCUACUGAUUAUCAUAAUGGUUGUCGUAGUGMet orstartPheLeuLeulleValUCUUCCUCAUCGCCUCCCCCACCGACUACCACAACGGCUGCCGCAGCGSerProThrAlaUAUUACUGUUGCTyr CysCAUCACCAACAGCGUCGCCGACGGAAUAACAAAAAGAGUAGCAGAAGGGAUGACGAAGAGGGUGGCGGAGGGUGGUAAUAGStopStopUGAStopTrpHisGlnAsnLysAspArgSerArgGlyUCAGUCAGUCAGUCAGFirst mRNA base (5 end)Third mRNA base (3 end)GluFig. 17-6(a) Tobacco plant expressing a firefly gene(b) Pig expressing a jellyfish geneSynthesis of an RNA Transcript•The stages of transcription are–Initiation–Elongation–TerminationFigure 17.7PromoterTranscription unitRNA polymeraseStart point533535535335533555RewoundDNARNAtranscript33Completed RNA transcriptUnwoundDNARNAtranscriptTemplate strand of DNADNA1Initiation. After RNA polymerase binds to the promoter, the DNA strands unwind, and the polymerase initiates RNA synthesis at the start point on the template strand.2Elongation. The polymerase moves downstream, unwinding theDNA and elongating the RNA transcript 5  3 . In the wake of transcription, the DNA strands re-form a double helix.3Termination. Eventually, the RNAtranscript is released, and the polymerase detaches from the DNA.RNA Polymerase Binding and Initiation of Transcription•Promoters signal the Initiation of RNA synthesis (TATA box)•Transcription factors–Help eukaryotic RNA polymerase recognize promoter sequencesFigure 17.8TRANSCRIPTIONRNA PROCESSINGTRANSLATIONDNAPre-mRNAmRNARibosomePolypeptideT A T A AAAA T A T T T TTATA boxStart pointTemplateDNA strand5335Transcriptionfactors5335Promoter53355RNA polymerase IITranscription factorsRNA transcriptTranscription initiation complexEukaryotic promoters1Several transcriptionfactors2Additional transcriptionfactors3Elongation of the RNA Strand•As RNA polymerase moves along the DNA–It continues to untwist the double helix, exposing about 10 to 20 DNA bases at a time for pairing with RNA nucleotidesElongationRNApolymeraseNon-templatestrand of DNARNA nucleotides3 endCA EGCAAUTAGGTTAACGUATCATC C AATTGG355Newly madeRNADirection of transcription(“downstream”)Templatestrand of DNAAlteration of mRNA Ends•Each end of a pre-mRNA molecule is modified in a particular way–The 5 end receives a modified nucleotide cap–The 3 end gets a poly-A tail–Modified ends help to 1)export mRNA from the nucleus 2) protect the mRNA from degradation in the cytoplasm and 3) facilitate ribosome attachmentFigure 17.9A modified guanine nucleotideadded to the 5 end50 to 250 adenine nucleotidesadded to the 3 endProtein-coding segmentPolyadenylation signalPoly-A tail3 UTRStop codonStart codon5 Cap5 UTRAAUAAAAAA…AAATRANSCRIPTIONRNA PROCESSINGDNAPre-mRNAmRNATRANSLATIONRibosomePolypeptideGPP P53Split Genes and RNA Splicing•RNA splicing–Removes introns (non-coding) and joins exons (coding regions)Figure 17.10TRANSCRIPTIONRNA PROCESSINGDNAPre-mRNAmRNATRANSLATIONRibosomePolypeptide5 CapExonIntron153031ExonIntron104 105 146Exon3Poly-A tailPoly-A tailIntrons cut out andexons spliced togetherCodingsegment5 Cap11463 UTR3 UTRPre-mRNAmRNA•DNA molecule consists of coding and non-coding regionsTranslation•Translation: the basic conceptFigure 17.13TRANSCRIPTIONTRANSLATIONDNAmRNARibosomePolypeptidePolypeptideAminoacidstRNA withamino acidattachedRibosometRNAAnticodonmRNATrpPheGlyAGCAA ACCGUGG U U UG GCCodons53The Structure and Function of Transfer RNAACC•A tRNA molecule–Consists of a single RNA strand that is only about 80 nucleotides long–Is roughly L-shapedFigure 17.14a-cTwo-dimensional structure. The four base-paired regions and three loops are characteristic of all tRNAs, as is the base sequence of the amino acid attachment site at the 3 end. The anticodon triplet is unique to each tRNA type. (The asterisks mark bases that have been chemically modified, a characteristic of tRNA.)(a)3CCACGCUUAAGACACCU*GC**GU G U*CU*G AGGU**A*AAGUCAGACC*CG AGAGGG**GACUC*AUUUAGGCG5Amino acidattachment siteHydrogenbondsAnticodonA(b) Three-dimensional structureSymbol used in this bookAmino acidattachment siteHydrogen bondsAnticodonAnticodonAAG533 5(c)Ribosomes•The ribosomal subunits are constructed of proteins and RNA molecules named ribosomal RNA or rRNATRANSCRIPTIONTRANSLATIONDNAmRNARibosomePolypeptideExit tunnelGrowingpolypeptidetRNAmoleculesEPALargesubunitSmallsubunitmRNA53Figure 17.16a•The ribosome has three binding sites for tRNA–The P site–The A site–The E siteFigure 17.16bE P AP site (Peptidyl-tRNAbinding site)E site (Exit site)mRNAbinding siteA site (Aminoacyl-tRNA binding site)LargesubunitSmallsubunitSchematic model showing binding sites. A ribosome has an mRNA binding site and three tRNA binding sites, known as the A, P, and E sites. This schematic ribosome will appear in later diagrams.(b)TranslationFigure 17.16cAmino endGrowing polypeptideNext amino


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