Biology Notes

Biology Notes - Chapter 17 Control of Gene Expression in Bacteria • How bacterial cells control the activity of their genes is a fundamental

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Chapter 17: Control of Gene Expression in Bacteria • How bacterial cells control the activity of their genes is a fundamental issue in biological science. • Gene expression occurs when a protein or other gene product is synthesized and is active in the cell. 17.1 Gene Regulation and Information Flow • Escherichia coli has served as an excellent model organism for the study of prokaryotic gene regulation because, like most bacteria, it can use a wide array of carbohydrates to supply carbon and energy. • Producing all the enzymes required to process all the various carbohydrates all the time would waste energy. It is logical to predict that the enzymes E. coli produces match the sugars that are available at a given time. • Efficient use of resources, via tight control over gene expression, is critical for E. coli 's survival. Mechanisms of Regulation: An Overview • Gene regulation can be transcriptional, translational, or post-translational ( Figure 17.1 ). • All three types of regulation occur in bacteria. Transcriptional control is slow but efficient. Translational control allows a cell to change quickly which proteins are produced. Post-translational control provides the most rapid response. Metabolizing Lactose: A Model System • Glucose is the preferred carbon source for E. coli . Lactose is used only when glucose is depleted. • E. coli produces high levels of Β-galactosidase, the enzyme that cleaves lactose to glucose + galactose, only when lactose is present in the environment. Thus, lactose acts as an inducer-a molecule that stimulates the expression of a specific gene. • Jacques Monod found that Β-galactosidase is not expressed in E. coli cells grown in medium containing glucose or glucose + lactose but only in medium containing lactose and no glucose. 17.2 Identifying the Genes Involved in Lactose Metabolism • To find the genes that code for Β-galactosidase and the membrane transport protein that brings lactose into the cell, Monod and Jacobs isolated and analyzed mutant individuals. Their goal was to find E. coli cells that could not metabolize lactose. Screening Mutants: Replica Plating and Indicator Plates • Master plates containing medium with many sugars were replica-plated to medium with lactose as the only sugar to screen for colonies that could not grow on lactose • Indicator plates allow mutants with metabolic deficiencies to be observed directly. Colonies grown on lactose were sprayed with ONPG (o-nitrophenol-Β- D-galactoside), an indicator with a structure similar to that of lactose. When Β- galactosidase breaks down ONPG, the intensely yellow compound o-nitrophenol is produced, turning colonies bright yellow....
View Full Document

This note was uploaded on 04/29/2008 for the course BIOL 201 taught by Professor Kittleson during the Spring '08 term at UVA.

Page1 / 55

Biology Notes - Chapter 17 Control of Gene Expression in Bacteria • How bacterial cells control the activity of their genes is a fundamental

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online