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The Central Dogma of Life.Protein SynthesisTranscription and TranslationSlide 4Slide 5TranscriptionRNASynthesis of an RNA TranscriptSlide 9Synthesis of an RNA Transcript - ElongationSynthesis of an RNA Transcript - TerminationTranscription OverviewSlide 13Alteration of mRNA EndsRNA Processing - SplicingSlide 16RNA ProcessingAlternative Splicing (of Exons)Slide 19TranslationThe Genetic CodeSlide 22Slide 23Transfer RNASlide 25RibosomesRibosomeBuilding a PolypeptideBuilding a Molecule of tRNASlide 30Initiation of TranslationElongation of the Polypeptide ChainTermination of TranslationTranslation: InitiationTranslation: ElongationSlide 36Translation: TerminationPolyribosomesComparing Gene Expression In Prokaryotes And EukaryotesA summary of transcription and translation in a eukaryotic cellPost-translationTargeting Polypeptides to Specific LocationsSlide 43Mutation Causes and RateMutagensViral MutagensPoint mutationsPoint MutationTypes of Point MutationsBase-Pair SubstitutionsInsertions and DeletionsThe Central Dogma of Life.replicationProtein Synthesis•The information content of DNA is in the form of specific sequences of nucleotides along the DNA strands•The DNA inherited by an organism leads to specific traits by dictating the synthesis of proteins•The process by which DNA directs protein synthesis, gene expression includes two stages, called transcription and translationTranscription and Translation•Cells are governed by a cellular chain of command–DNA RNA protein•Transcription–Is the synthesis of RNA under the direction of DNA–Produces messenger RNA (mRNA)•Translation–Is the actual synthesis of a polypeptide, which occurs under the direction of mRNA–Occurs on ribosomesTranscription and Translation•In prokaryotes transcription and translation occur togetherFigure 17.3aProkaryotic cell. In a cell lacking a nucleus, mRNAproduced by transcription is immediately translatedwithout additional processing.(a)TRANSLATIONTRANSCRIPTIONDNAmRNARibosomePolypeptideTranscription and Translation•In a eukaryotic cell the nuclear envelope separates transcription from translation•Extensive RNA processing occurs in the nucleusEukaryotic cell. The nucleus provides a separatecompartment for transcription. The original RNAtranscript, called pre-mRNA, is processed in various ways before leaving the nucleus as mRNA.(b)TRANSCRIPTIONRNA PROCESSINGTRANSLATIONmRNADNAPre-mRNAPolypeptideRibosomeNuclearenvelopeTranscription•Transcription is the DNA-directed synthesis of RNA•RNA synthesis–Is catalyzed by RNA polymerase, which pries the DNA strands apart and hooks together the RNA nucleotides–Follows the same base-pairing rules as DNA, except that in RNA, uracil substitutes for thymineRNATable 17.1•RNA is single stranded, not double stranded like DNA•RNA is short, only 1 gene long, where DNA is very long and contains many genes•RNA uses the sugar ribose instead of deoxyribose in DNA•RNA uses the base uracil (U) instead of thymine (T) in DNA.Synthesis of an RNA Transcript•The stages of transcription are–Initiation–Elongation–TerminationPromoterTranscription unitRNA polymeraseStart point533535535335533555RewoundRNARNAtranscript3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.•Promoters signal the initiation of RNA synthesis•Transcription factors help eukaryotic RNA polymerase recognize promoter sequences•A crucial promoter DNA sequence is called a TATA box.TRANSCRIPTIONRNA PROCESSINGTRANSLATIONDNAPre-mRNAmRNARibosomePolypeptideT A T AAAAAT AT 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 transcriptionfactors3Synthesis of an RNA Transcript - InitiationSynthesis of an RNA Transcript - ElongationElongationRNApolymeraseNon-templatestrand of DNARNA nucleotides3 endCAEGCAAUTAGGTTAACGUATCATC C AATTGG355Newly madeRNADirection of transcription(“downstream”)Templatestrand of DNA•RNA polymerase synthesizes a single strand of RNA against the DNA template strand (anti-sense strand), adding nucleotides to the 3’ end of the RNA chain•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 nucleotides•Specific sequences in the DNA signal termination of transcription•When one of these is encountered by the polymerase, the RNA transcript is released from the DNA and the double helix can zip up again.Synthesis of an RNA Transcript - TerminationTranscription Overview•Most eukaryotic mRNAs aren’t ready to be translated into protein directly after being transcribed from DNA. mRNA requires processing.•Transcription of RNA processing occur in the nucleus. After this, the messenger RNA moves to the cytoplasm for translation.•The cell adds a protective cap to one end, and a tail of A’s to the other end. These both function to protect the RNA from enzymes that would degrade •Most of the genome consists of non-coding regions called introns–Non-coding regions may have specific chromosomal functions or have regulatory purposes–Introns also allow for alternative RNA splicing•Thus, an RNA copy of a gene is converted into messenger RNA by doing 2 things:–Add protective bases to the ends–Cut out the intronsPost Termination RNA ProcessingAlteration 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 tailA 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


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ACC BIO 1308 - Protein Synthesis

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