Question

What is FALSE about E coli and the lac operon? A. The lac Y and lac Z genes are turned off when lactose is present.B. The lac Y and lac Z genes are turned off when glucose is present. C. Lactose is a disaccharide which requires more energy to eat than the monosaccharide glucose. D. The lac Y gene encodes the permease protein. E. B-galactosidase breaks the covalent bond between the glucose and galactose of the lactose molecule.

Answer 1

Answer: The lac Y and lac Z genes are turned off when lactose is present. Is a false statement about E coli and the lac operon. Therefore the correct option is A.

Explanation:

Escherichia coli is an enteric bacteria that makes use of lactose operon (or lac operon) for its lactose metabolism. The lac operon is made up of three genes which includes lacZ, lacY and Lac A. These genes are expressed only when lactose is present and glucose is absent. Also the lac repressor acts as a lactose sensor while the catabolite activation protein (CAP) acts as a glucose sensor. They help in turning on and off the genes with respect to lactose and glucose levels.

The lac Y and lac Z genes are turned off (not expressed) when glucose is present and lactose absent, but are expressed when glucose is absent and lactose present. Therefore option A is a false statement.