Chapter 18 - Operon Notes

Chapter 18 - Operon Notes - Regulation of Gene Expression...

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H:\AP Biology\Homework and Handout\Operon Notes.doc 1 Regulation of Gene Expression in Prokaryotes Operons Prokaryotes must use substances and synthesize macromolecules just fast enough to meet their needs. If enzymes needed, gene transcribed. If enzyme not needed, gene turned off. Allows for conservation of cell resources. Controlling gene expression is one method of regulating metabolism. The other method of controlling metabolism involves (you should know this!) Operon --Genes grouped together; transcribed into single mRNA molecule containing coding sequences for more than one gene ( polycistronic gene ; “ cistron ”= gene). Grouped together with one promoter. Operons can be inducible or repressible . Inducible products are made when the substrate is in the environment (lactose) and needs to be metabolized. Repressible products are made when a signal molecule is scarce (ie. Biosynthetic pathways such as tryptophan) Allows for coordinated control of genes required for metabolism. One switch controls more than one gene. Not present in Eukaryotes. Eukaryotes have more complex methods of controlling gene expression. (Next Chapter!) Binding of repressor to operator prevents transcription – GENE OFF [RNA poly-ase not able to bind to promoter]. Operators
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Chapter 18 - Operon Notes - Regulation of Gene Expression...

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