Suppose that you perform an experiment where you construct a plasmid that carries a copy of the lac operator region (lacO) but no other part of the lac operon. (The lac repressor can bind to single operator regions.) This plasmid is placed in an E. coli cell, which has a normal copy of the lac operon in its chromosome. When this strain is grown, the number of plasmids reaches about 50 copies per bacterial cell. What is the expected phenotype of such a strain in the absence of glucose?
A) The lac operon will be turned on even in the absence of lactose.
B) The lac operon will be turned off even in the presence of lactose.
C) The lac operon will be regulated normally.
D) The lac operon will be initially turned on in the presence of lactose but eventually it will be turned off even though lactose is still present.
E) The lac operon will be expressed only if galactose is added to the Moderate.

Question

Quizplus · Accepted Answer

The excess lac operator regions from the plasmids will bind the lac repressor proteins, preventing them from binding to the chromosomal lac operon, thus keeping it off even in the presence of lactose.

Suppose That You Perform an Experiment Where You Construct a Plasmid