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Gene Regulation Expression of certain genes in any given cell Mechanisms That Regulate Gene Expression Amount of mRNA transcribed Rate of translation Activity of protein product Bacterial Gene Regulation Transcription-level control is most efficient Constitutive genes are constantly transcribed Genes that are needed only under certain conditions are arranged in operons Operons Groups of structural genes with related functions + DNA responsible for controlling them: Promoter – site for RNA polymerase to bind Operator – switch that controls transcription The lac Operon Produces enzymes for lactose digestion Only needed when no glucose present but lactose is http://highered.mcgrawhill.com/sites/0072437316/student_view0/cha pter18/animations.html# Gene Regulation in Eukaryotes Transcriptional controls Posttranscriptional controls Posttranslational modification Eukaryotic Transcriptional Controls Heterochromatin – tightly coiled cannot be transcribed DNA methylation – adding methyl groups to cytosine nucleotides – no transcription Multiple copies of genes – tandem repeats Selective gene amplification – certain cells TATA box required for transcription to begin Promoter 25-35 bp upstream from gene RNA polymerase binds Upstream promoter elements 100-200 bp upstream from RNA polymerase binding site Regulatory proteins bind to UPEs # of UPEs affects expression Enhancers Help to initiate transcription May be located far from gene Transcription factors Proteins that bind to DNA (enhancers and UPEs) Posttranscriptional controls Addition of poly-A tail 5’ cap May prevent degradation Intitiates translation Longer tail, more efficient translation Prevents degradation Differential mRNA processing Posttranslational control Allosteric enzymes regulated through feedback inhibition Proteolytic processing Proteins made as inactive precursors Chemical modification Ex. Kinases add phosphate groups