Chapter 17Overview: The Flow of Genetic InformationSlide 3Concept 17.1: Genes specify proteins via transcription and translationEvidence from the Study of Metabolic DefectsNutritional Mutants in Neurospora: Scientific InquiryLE 17-2The Products of Gene Expression: A Developing StoryBasic Principles of Transcription and TranslationSlide 10LE 17-3-1LE 17-3-2LE 17-3-3LE 17-3-4LE 17-3-5The Genetic CodeCodons: Triplets of BasesSlide 18LE 17-4Cracking the CodeLE 17-5Evolution of the Genetic CodeSlide 23Concept 17.2: Transcription is the DNA-directed synthesis of RNA: a closer lookMolecular Components of TranscriptionSlide 26LE 17-7Slide 28Slide 29Slide 30Slide 31Synthesis of an RNA TranscriptRNA Polymerase Binding and Initiation of TranscriptionLE 17-8Elongation of the RNA StrandTermination of TranscriptionConcept 17.3: Eukaryotic cells modify RNA after transcriptionAlteration of mRNA EndsLE 17-9Split Genes and RNA SplicingLE 17-10Slide 42LE 17-11RibozymesThe Functional and Evolutionary Importance of IntronsSlide 46LE 17-12Concept 17.4: Translation is the RNA-directed synthesis of a polypeptide: a closer lookMolecular Components of TranslationLE 17-13The Structure and Function of Transfer RNALE 17-14aSlide 53LE 17-14bSlide 55LE 17-15RibosomesLE 17-16aSlide 59LE 17-16bLE 17-16cBuilding a PolypeptideRibosome Association and Initiation of TranslationLE 17-17Elongation of the Polypeptide ChainLE 17-18Termination of TranslationLE 17-19PolyribosomesLE 17-20Completing and Targeting the Functional ProteinProtein Folding and Post-Translational ModificationsTargeting Polypeptides to Specific LocationsSlide 74LE 17-21Concept 17.5: RNA plays multiple roles in the cell: a reviewSlide 77Slide 78Slide 79Concept 17.6: Comparing gene expression in prokaryotes and eukaryotes reveals key differencesLE 17-22Concept 17.7: Point mutations can affect protein structure and functionLE 17-23Types of Point MutationsSubstitutionsLE 17-24Insertions and DeletionsLE 17-25MutagensWhat is a gene? revisiting the questionLE 17-26Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsPowerPoint Lectures for Biology, Seventh EditionNeil Campbell and Jane ReeceLectures by Chris RomeroChapter 17Chapter 17From Gene to ProteinCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsOverview: The Flow of Genetic Information•The information content of DNA is in the form of specific sequences of nucleotides•The DNA inherited by an organism leads to specific traits by dictating the synthesis of proteins•Gene expression, the process by which DNA directs protein synthesis, includes two stages: transcription and translation•The ribosome is part of the cellular machinery for translation, polypeptide synthesisCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsConcept 17.1: Genes specify proteins via transcription and translation•How was the fundamental relationship between genes and proteins discovered?Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsEvidence from the Study of Metabolic Defects•In 1909, British physician Archibald Garrod first suggested that genes dictate phenotypes through enzymes that catalyze specific chemical reactions•He thought symptoms of an inherited disease reflect an inability to synthesize a certain enzyme•Linking genes to enzymes required understanding that cells synthesize and degrade molecules in a series of steps, a metabolic pathwayCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsNutritional Mutants in Neurospora: Scientific Inquiry•Beadle and Tatum exposed bread mold to X-rays, creating mutants that were unable to survive on minimal medium as a result of inability to synthesize certain molecules•Using crosses, they identified three classes of arginine-deficient mutants, each lacking a different enzyme necessary for synthesizing arginine•They developed a “one gene–one enzyme” hypothesis, which states that each gene dictates production of a specific enzymeLE 17-2LE 17-2Class IMutants(mutationIn gene A)Wild typeClass IIMutants(mutationIn gene B)Class IIIMutants(mutationIn gene C)PrecursorOrnithineAEnzymeACitrullineArginineGene AGene BGene CPrecursor Precursor PrecursorAAB B BOrnithine Ornithine OrnithineEnzymeBEnzymeCArginine Arginine ArginineC C CCitrulline Citrulline CitrullineMinimalMedium(MM)(control)Wild typeClass IMutantsClass IIMutantsClass IIIMutantsMM +OrnithineMM +CitrullineMM +arginine(control)Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsThe Products of Gene Expression: A Developing Story•Some proteins aren’t enzymes, so researchers later revised the hypothesis: one gene–one protein•Many proteins are composed of several polypeptides, each of which has its own gene•Therefore, Beadle and Tatum’s hypothesis is now restated as one gene–one polypeptideCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsBasic Principles of Transcription and Translation•Transcription is the synthesis of RNA under the direction of DNA•Transcription produces messenger RNA (mRNA)•Translation is the synthesis of a polypeptide, which occurs under the direction of mRNA•Ribosomes are the sites of translationCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings•In prokaryotes, mRNA produced by transcription is immediately translated without more processing•In a eukaryotic cell, the nuclear envelope separates transcription from translation •Eukaryotic RNA transcripts are modified through RNA processing to yield finished mRNA•Cells are governed by a cellular chain of command: DNA RNA proteinLE 17-3-1LE 17-3-1TRANSCRIPTIONDNAProkaryotic cellLE 17-3-2LE 17-3-2TRANSCRIPTIONDNAProkaryotic cellRibosomePolypeptidemRNAProkaryotic cellLE 17-3-3LE 17-3-3TRANSCRIPTIONTRANSLATIONDNAmRNARibosomePolypeptideDNAProkaryotic cellNuclearenvelopeTRANSCRIPTIONEukaryotic cellLE 17-3-4LE 17-3-4TRANSCRIPTIONTRANSLATIONDNAmRNARibosomePolypeptideDNAPre-mRNAProkaryotic cellNuclearenvelopemRNATRANSCRIPTIONRNA PROCESSINGEukaryotic cellLE 17-3-5LE 17-3-5TRANSCRIPTIONTRANSLATIONDNAmRNARibosomePolypeptideDNAPre-mRNAProkaryotic cellNuclearenvelopemRNATRANSLATIONTRANSCRIPTIONRNA PROCESSINGRibosomePolypeptideEukaryotic cellCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsThe Genetic Code•How are the instructions for