Regulation of Gene Expression: Turning Genes On and Off

 

Tested Studies in Laboratory Teaching, 2010, Volume 31

Doonan, C.

Abstract

This experiment demonstrates that expression of the lactose genes of E. coli are regulated by the availability of certain small sugar molecules. Bacteria cells prefer glucose as a carbon source as the cells can readily use it. The disaccharide lactose must first be converted to glucose and galactose monomers by the enzyme, Β-galactosidase, one of the three enzymes involved in the utilization of lactose. In this experiment, the growth of two bacterial cultures is monitored and samples are removed at regular intervals to assay for the enzyme Β-galactosidase. Students observe how the activity of this enzyme changes upon the addition of different sugars to the growth medium. Students will also demonstrate that the genes can be turned off again by the addition of the preferred sugar, glucose. Each group of students will have two cultures. To the first, they will add lactose and then glucose. The second flask serves as a control where students must choose whether to add glucose, lactose or galactose to the culture. Based on what is known about the regulation of the genes of the lac operon, students can predict the effect of each of these sugars on the intercellular levels of Β-galactosidase. Upon completion of the lab experiment, students will measure and graph the growth of bacteria, and quantitate the amount of the enzyme Β-galactosidase produced by the cells. They can assess the validity of their hypothesis on sugar utilization by the bacterial cells by analyzing their results.

Keywords:  beta galactosidase, gene regulation, E. Coli growth, Quantitation of Betagalactosidase, gene expression

University of Delaware (2009)