Question

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what happens to e. coli when lactose is not present?
○ e. coli is not able to survive without lactose.
○ the genes required to produce the enzymes that break down lactose are destroyed.
○ the genes that produce the enzymes needed to break down lactose are not expressed.
○ the enzymes needed to break down lactose are continually produced.

Explanation:

When lactose is not present in \(E. coli\), the lac operon (a set of genes involved in lactose metabolism) is repressed. A repressor protein binds to the operator region of the lac operon, preventing RNA polymerase from transcribing the genes that code for the enzymes (such as \(\beta -\)galactosidase) needed to break down lactose. The genes themselves are not destroyed (they are part of the \(E. coli\) genome), and \(E. coli\) can survive on other carbon sources (like glucose). Also, the enzymes are not produced continuously in the absence of lactose because that would be a waste of energy and resources for the bacterium.

Answer:

The genes that produce the enzymes needed to break down lactose are not expressed.