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Gene Regulation: Prokaryotes and Eukaryotes Chapter 11 Lac Operon OPERON Regulatory gene Promoter Operator Lactose-utilization genes DNA mRNA Protein RNA polymerase cannot attach to promoter Active repressor Operon turned off (lactose absent) DNA RNA polymerase bound to promoter mRNA Protein Lactose Inactive repressor Operon turned on (lactose inactivates repressor) Enzymes for lactose utilization Trp Operon trp operon Promoter DNA Promoter Genes of operon trpD trpC trpE trpR trpB trpA Operator Regulatory gene mRNA 5 3 RNA polymerase Start codon Stop codon mRNA 5 E Protein Inactive repressor D C B A Polypeptides that make up enzymes for tryptophan synthesis (a) Tryptophan absent, repressor inactive, operon on. RNA polymerase attaches to the DNA at the promoter and transcribes the operon’s genes. Trp Operon DNA No RNA made mRNA Protein Active repressor Tryptophan (corepressor) (b) Tryptophan present, repressor active, operon off. As tryptophan accumulates, it inhibits its own production by activating the repressor protein. Levels of Chromatin Packing X chromosome Inactivation and Tortoiseshell Cat Tortiseshell Cat X chromosome Inactivation in a Calico Cat Cellular Differentiation Muscle cell Pancreas cells Blood cells Enhancers Promoter Gene DNA Activator proteins Transcription factors Other proteins RNA polymerase Bending of DNA Transcription Eukaryotic Transcription: Enhancers, Activators Production of two different mRNAs from the same gene Exons DNA RNA transcript or RNA splicing mRNA Alternative Gene Splicing NUCLEUS Chromosome Overview: Opportunities for gene regulation in eukaryotic cells DNA unpacking Other changes to DNA Gene Gene Transcription Exon RNA transcript Intron Addition of cap and tail Tail Splicing mRNA in nucleus Cap Flow through nuclear envelope mRNA in cytoplasm CYTOPLASM Breakdown of mRNA Translation Brokendown mRNA Polypeptide Cleavage / modification / activation Active protein Breakdown of protein Brokendown protein