Operons are made of two or more genes that are located near each other in a sequence of DNA. Some operons allow for regulation of the expression of proteins at the transcriptional level. As a result, some operons are inducible, while others repressible. Which of the following represents an inducible operon? a. The production of enzymes that allow for the fermentation of the sugar lactose when it becomes available in the culture medium b. The enzymes needed for glucose metabolism are always produced at a constant level. c. Proteases break down proteins when they are no longer necessary. d. The discontinued production of the enzymes needed to synthesize the amino acid tryptophan if it is added to the growth medium

a. The production of enzymes that allow for the fermentation of the sugar lactose when it becomes available in the culture medium

Explanation:

When an operon that is normally not expressed and remains inactive since a repressor molecule is attached to its operator, it is said to be an inducible operon. The transcription of the operon is activated when an inducer binds to the repressor. This binding does not allow the repressor protein to bind to the operator. The operon is transcribed by RNA polymerase.

When lactose is present in the medium, the lac operon is expressed.  Some of the lactose is converted into allolactose. Allolactose binds to the repressor and makes it unable to bind to the operator. This makes it an inducible operon.  

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