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Unformatted text preview: 1 B I O L O G Y 0 2 3 Control of Gene Expression Chapter 15 B I O L O G Y 0 2 3 Gene Expression Control • All somatic cells in an organism are genetically identical – Cells differentiate by gene expression • Gene expression is collectively controlled through transcriptional regulation – Main control: Gene transcribed into mRNA B I O L O G Y 0 2 3 Operon: Unit of Transcription • Prokaryotic gene expression reflects life history – Rapid, reversable response to environment • Operon : A cluster of prokaryotic genes and DNA sequences involved in their regulation – RNA polymerase binds at promoter for B I O L O G Y 0 2 3 Operon: Unit of Transcription (cont’d) • Other regulatory DNA sequence in operon is the operator – Regulatory protein coded by gene outside operon • Repressor proteins prevent operon genes from being expressed • Activator proteins turn on expression E. coli lac Operon Fig. 15-2, p. 323 B I O L O G Y 0 2 3 15.2 Regulation of Transcription in Eukaryotes...
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