BSC 2010 Chapter 18: Biology Ch. 18 Notes Part 1 BSC2010
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Department
Biological Science
Course Code
BSC 2010
Professor
Kevin Dixon

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18.1 Bacteria respond to environmental change by regulating transcription of gene clusters ● Gene expression in bacteria is controlled by genes ● Natural selection has favored bacteria that produce only the products needed by that cell ○ Metabolic pathways must be controlled ○ Metabolic pathways must respond to changes in the cell’s environment ● A cell can regulate the production of enzymes by feedback inhibition or by gene regulation ● Cells control metabolism by regulating enzyme activity or the expression of genes coding for enzymes. In bacteria, genes are often clustered into operons, with one promoter serving several adjacent genes. ○ Operons- a cluster of functionally regulated genes that can be controlled by a single “on-off” switch ■ Function is controlled through the operator ○ The “switch” is a part of DNA called an operator which is usually located in the promoter ■ Promoter- a specific nucleotide sequence in the DNA of a gene that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place ● Both repressible and inducible operons are negative gene regulation. In either type of operon, binding of a specific repressor protein to the operator shuts off transcription. ○ The repressor is encoded by a separate regulatory gene ■ Repressors- turn operator function off (repress the transcription of the genes in the operon) and are in turn controlled by other molecules ○ In a responsible operon, the repressor is active when bound to a corepressor, usually the end product of an anabolic pathway ■ Corepressors- activate repressors and help to repress transcription of the genes in the operon ○ In an inducible operon, binding of an inducer to an innately active repressor inactivates the repressor and turns on transcription. Inducible enzymes usually function in catabolic pathways ■ Inducers- repress the repressors and activate transcription of genes in the operon ○ Some operons are also subject to positive gene regulation via a stimulatory activator protein, such as a catabolite activator protein (CAP), which, when activated b
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