Lecture 18

Lecture 18 - Biol142 Foundations in Modern Biology II...

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Unformatted text preview: Biol142 Foundations in Modern Biology II Cellular Biology and Genetics Lecture 18 – Friday, March 2 nd , 2012 Prokaryotic Gene Regulation III Reading: Freeman, Emory 2 nd Ed. Chapter 17 (pages 314 - 317) Learning objectives At the end of this lecture, you will be able to: 1) Describe the inducible lac operon system of E coli . 2) Explain why the lac operon transcription is only fully activated when lactose is available and when glucose is scarce. 3) Compare and contrast the lac operon and the trp operon . 1. Recap: The genes involved in lactose metabolism are adjacent to each other on the E. coli chromosome. • lacZ, lacY, and lacA are all transcribed together to form a single mRNA when RNA polymerase binds a single promoter . • The whole unit of genes and their DNA controls is called an operon —the operon for the lactose- metabolizing enzymes is called the lac operon . Prokaryotes shut down transcription by placing an obstacle between the promoter and the lac genes, called the operator . ! If a specific protein, the repressor , binds to the operator , it creates an obstacle, and RNA polymerase is blocked from transcribing the lac genes. • When lactose concentration drops , the functioning repressor binds the operator , and the lactose metabolism enzymes are not synthesized. The repressor protein has two binding sites: one...
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This note was uploaded on 04/02/2012 for the course BIO 142 taught by Professor Escabar during the Spring '08 term at Emory.

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Lecture 18 - Biol142 Foundations in Modern Biology II...

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