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Chapter 14

Chapter 14 - Gene Structure and Expression.docx

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Department
Biology
Course
BIOL 204
Professor
Dr.Roland Treu
Semester
Spring

Description
CHAPTER 14 GENE STRUCTURE AND EXPRESSION141 The Connection between DNA RNA and Protein141a Genes Specify Either Protein or RNA Products1896 Garrod studied alkaptonuria human disease that does little harm but detected easily urine turns black in airParticular chemical excreted in urine and this chemical turns black in airNormal people able to metabolize the chemical whereas people w alkaptonuria cannot oConcluded TF disease is inborn error of metabolism He dN know but defect aar of alteration of gene that encodes enzyme that metabolizes key chemicaloAltered gene causes defect in function of enzyme which leads to phenotype of disease1940s BeadleTatum collected data showing direct rlnshp btwn genesenzymes w orange bread mould Neurospora crassais haploid fungus w simple nutritional needsGrows readily on minimal medium MM consistingof inorganic salts sucrose and a vitaminoReasoned fungus uses simplechemicals in medium to synthesize more complex molecules needed for growthreproduction AA for proteins nucleotides for DNARNAExposed spores of wildtype to Xrays causes mutationsoSome treated spores would not germinategrow unless MM supplemented w nutrients AAsvitaminsoMutant strains unable to grow on MMauxotrophs auxoincreased tropheater or nutritional mutantsH each auxotrophic strain had defect in gene coding for enzyme needed to synthesize nutrient that now 1had to be added to MMoBy testing to see if each mutant strain would grow on MM supplemented w given nutrient able to discover which specific nutrient needed for growth and TF which gene defect it hadoEx arg mutantsmutant that reqd addition of AA arginine to grow w defect in gene for enzyme involved in synthesis of arginineAssembly of arginine from raw materials is multistep assemblyline process w diff enzyme catalyzing each step TF diff arg mutant might differ in the particular enzyme that is defective and therefore in which step of assembly pathway is blockedargE argF argG argHTested whether each mutant could grow on MM or on MM supplemented w ornithine citruline argininosuccinate or arginine itselfNone grew on MM but did on MMarg itselfEach arg mutant showed different pattern of growth on supplemented MMoDeduced biosynthesis of arginine occurred inof steps w each step controlled by gene that encoded enzyme for the stepAs seen above argH mutant grows on MMarginine but not on MMany other of 3 compoundsoMeans mutant blocked at last step in pathway which produces arginineW similar analysis deduced whole pathway from precursor to arginine and showed which gene encoded enzyme that carried out each stepIn sum Beadle and Tatum had shown direct relationship between genes and enzymesone geneone enzyme hypothesisImportant to understand many proteins NOT enzymes and many consist of 1 subunit called polypeptideoEx hemoglobin made up of 4 polypeptides twosubunits and twosubunits giving protein its functional property of transporting oxygen rather than catalyzing chemical reactionTwo diff genes needed to encode Hb protein one forand one for H later restated as one geneone polypeptide hypothesis1141b The Pathway from Gene to Polypeptide Involves Transcription and TranslationTranscriptionmechanisms by which info encoded in DNA made into complementary RNA copy info in one nucleic acid type transferred to another nucleic acid typeoEnzyme RNA polymerase creates RNA sequence complementary to DNA sequence of given gene
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