Gene Expression · Paper 1 — Free Biology HL Practice Questions

E. coli are grown in a medium containing only glucose as the sole carbon source. β-galactosidase activity is detected at very low levels. The bacteria are then transferred to a medium containing only lactose, and after 30 minutes β-galactosidase activity increases dramatically. Which statement best explains the low β-galactosidase activity in the glucose-only medium?

A mutant strain of Escherichia coli carries a complete deletion of the promoter region of the lac operon, preventing RNA polymerase from binding. The mutant is grown in a medium containing only lactose as the sole carbon source. Which of the following best predicts the outcome for expression of lacZ, lacY, and lacA?