The Trp Operon

How does the trp operon differ from the lac operon? The lac operon is involved with the breakdown of lactose to use as a food source. The trp operon produces products that are used to manufacture an amino acid, tryptophan. The pathway controlled by the trp operon is an example of an anabolic pathway. The lac operon controls a catabolic pathway, one that breaks down complex molecules to release energy for biological work. The lac operon is controlled both by the abundance of its substrate, lactose, and by the abundance of glucose, an alternative to glucose. As there is no alternative to tryptophan the control of the trp operon is less complex than that of the lac operon.

View the animation below, then complete the quiz to test your knowledge of the concept.


1	The trp operon consists of ________ structural genes.

		A)	one
		B)	two
		C)	three
		D)	four
		E)	five

2	In the absence of tryptophan, the trp repressor is

		A)	active and can bind to the operator.
		B)	active and cannot bind to the operator.
		C)	inactive and cannot bind to the promoter.
		D)	inactive and can bind to the operator.
		E)	inactive and cannot bind to the operator.

3	In the presence of tryptophan, tryptophan binds to the

		A)	operator.
		B)	promoter.
		C)	RNA polymerase.
		D)	trp genes.
		E)	trp repressor.

4	In the presence of tryptophan, transcription of the trp operon is on.

		A)	True
		B)	False

5	An operon is a group of genes that is under the control of a singe operator site.

		A)	True
		B)	False

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