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Which of the following is true of the lac operon in E. coli?

A. The operon is switched on in the absence of lactose in the growth medium.
B. The lac operon messenger RNA is polycistronic as it carries information for the synthesis of several proteins.
C. The enzyme [tex]\(\beta\)[/tex]-galactosidase is only produced in large quantities when the lac repressor is bound to the operator.
D. The promoter is the binding site for the repressor protein.



Answer :

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Final answer:

The lac operon in E. coli is essential for lactose transport and metabolism, being regulated by lactose availability. It is switched on in the absence of lactose, features polycistronic mRNA, and ß-galactosidase production is controlled by the lac repressor.


Explanation:

The lac operon in E. coli:

  1. The operon is switched on in the absence of lactose in the growth medium: The lac operon is usually silent when glucose is the preferred energy source, but it becomes active when glucose levels are low, and lactose is present.
  2. The lac operon messenger RNA is polycistronic: It carries information for the synthesis of several proteins, including LacZ (ß-galactosidase), LacY (permease), and LacA (acetylase).
  3. The enzyme ß-galactosidase is only produced in large quantities when the lac repressor is bound to the operator: In the absence of lactose, the lac repressor binds to the operator, blocking transcription of the operon.

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