Chapter 15, Problem 1TYU

If a particular operon encodes enzymes for making an essential amino acid and is regulated like the trp operon, then

1. A.    the amino acid inactivates the repressor.
2. B.     the repressor is active in the absence of the amino acid.
3. C.     the amino acid acts as a corepressor.
4. D.    the amino acid turns on transcription of the operon.

Summary Introduction

Introduction:

Operon refers to the functional unit of the DNA (genomic). It consist of various genes that controls operon’s regulation. There are two types of operons; lac (lactose) and Trp (tryptophan).

Answer to Problem 1TYU

Correct answer:

If a particular operon encodes certain enzymes for forming an amino acid and is regulated as Trp operon, then the amino acid will be acting like a corepressor molecule. Therefore, option (C) is correct.

Explanation of Solution

Reason for the correct statement:

A Trp operon is a group of genes, which encodes certain enzymes (biosynthetic) for tryptophan. This is expressed when the levels of tryptophan is low. An operon that encodes certain enzymes for the formation of amino acids and acts like a Trp operon, then, the amino acids will act like a corepressor. A corepressor is a small molecule that cooperates with the repressor protein for switching the operon off.

Option (C) is given as “the amino acid acts as a corepressor”.

“If a particular operon encodes certain enzymes for forming an amino acid and is regulated as Trp operon, then the amino acid will be acting like a corepressor molecule”, it is the right answer.

Hence, the option (C) is correct.

Reasons for the incorrect statements:

Option (A) is given as “the amino acid inactivates the repressor”.

The amino acid will be acting like a corepressor, hence it will not inactivate the repressor, and however it will react with the repressor. So, it is a wrong answer.

Option (B) is given as “the repressor is active in the absence amino acid”.

If the operon has to be kept ON, then the repressor will be inactive in the absence of amino acid. So, it is a wrong answer.

Option (D) is given as “the amino acid turns on the transcription of operon”.

The amino acid is not responsible for turning the transcription ON. So, it is a wrong answer.

Hence, options (A), (B), and (D) are incorrect.

Conclusion

The amino acid will be acting like a corepressor molecule as if a particular operon encodes certain enzymes for forming an amino acid and is regulated as the Trp operon.