Chapter 13: Gene Regulation

Chapter 13: Gene Regulation1The Big PictureA cell contains more genes than it expresses at any given time why? Why are cells in multicellular organisms specialized and only express certain genes?Gene expression in cells must be regulated From inside the cellFrom outside the cell: by other nearby cells, or the environment2Bacterial Gene RegulationUnicellular with very short life spansControl gene regulation with control of transcription: transcriptional-level controlFunctionally related genes are controlled together in gene complexes called operons

3The bacterial lac operon: an exampleHelps E. coli bacteria metabolize lactoseRequires 3 different enzymes the lac operon has these genes all closely linked on the DNA strandTranscription for all 3 enzymes produces 1 mRNA strand with coding for each enzymeWithout the presence of lactose, a repressor protein prevents mRNA transcription of the lac operonIn the presence of lactose, this protein is altered and can no longer prevent transcriptionThis is an inducible operon it is usually off but can be turned on but the presence of an inducer molecule4Other forms of bacterial regulationRepressible operons: genes are usually turned on but are turned off under certain conditionsBoth inducible and repressible operons are negative controls: the regulatory protein is a repressor that turn off transcriptionPositive controls: use an activator protein that binds to DNA and stimulates transcription

5Other forms of bacterial regulationTranslational controls: the speed of mRNA tRNA protein is controlledPosttranslational controls: enzymes are turned off and on, rather than genesFeedback inhibition6Eukaryotic Gene RegulationCells must respond to changes in the environmentCells must become specialized and fulfill the specific roles of the tissues in the bodyEukaryotic cells rely on transcriptional, translational, and posttranslational controlsEukaryotic cells generally do not have operons7Eukaryotic Transcriptional RegulationTranscription requires the transcription initiation site plus the promoter in eukaryotes this is called a TATA box and is required for transcription to beginRNA polymerase binds to the TATA box Some promotes also have upstream promoter elements (UPEs) usually the more of these that are present, the more strongly a particular gene is expressed8Additional transcriptional regulationDNA sequences called enhancers increase the rate of transcriptionTranscription factors DNA-binding proteins that regulate transcriptionRNA interference small bits of RNA permanently shut down sections of DNADNA methylation DNA has been chemically altered by enzymes that add methyl groups to cytosine9Eukaryotic Posttranscriptional ControlAfter transcription mRNA is further processed before translationThese event provide points of control between transcription and translationSome proteins are further modified after translation by adding or removing functional groups

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