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Biology Chapter 17.docx

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Lovaye Kajiura

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Biology Chapter 17: Control of Gene Expression in Bacteria Bernard Ho December 3, 2010 Gene Regulation and Information Flow − Gene expression occurs when a gene product is actively being synthesized and used in a cell − Regulation of gene expression is critical to the efficient use of resources and so to survival − E. coli has served as an excellent model organism for the study of prokaryotic gene regulation o Like most bacteria, E. coli can use a wide array of carbohydrates to supply carbon and energy o Control of gene expression allows E. coli to respond to its environment and switch its use of sugars − Transcription and translation of genes in bacteria were predicted to be triggered by specific signals from the environment − Gene expression can be controlled at any step between the synthesis of RNA and the activation of the final gene product − DNA  mRNA  protein  activated protein o Arrow from DNA to RNA represents transcription, the making of mRNA o Arrow from RNA to protein represents translation, in which ribosomes read the information in mRNA and use that information to synthesize a protein o Arrow from protein to activated protein represents post-translational modifications, folding, addition of carbohydrate or lipid groups − How can a bacterial cell avoid producing proteins that are not needed at a particular time and thus use resources efficiently o The cell could avoid making the mRNAs for particular enzymes  If there is no mRNA, then ribosomes cannot make the gene product  Ex. Various regulatory proteins affect the ability of RNA polymerase to bind to a promoter and initiate transcription  Genes that are controlled in this way are said to undergo transcriptional control o If mRNA for an enzyme has been transcribed, the cell might have a way to prevent the mRNA from being translated into protein  Mechanisms that alter the length of time an mRNA survives before it is degraded by ribonucleases, that affect translation initiation or that affect elongation factors and other proteins during the translation process a
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