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Chapter 16: Q. 1 (page 414)

In E. coli, the trp operon is on by default, while the lac operon is off. Why do you think that this is the case?

Short Answer

Expert verified

If there is already an abundance of tryptophan, producing more would be inefficient, and the trp receptor's expression would be suppressed. The lac operon is only activated when lactose is present since it makes no sense to produce the enzymes required to digest an energy source that is not there.

Step by step solution

01

Introduction

Amino acids are necessary for bacteria like E. coli to live. One of these amino acids that E. coli can take in from the environment is tryptophan. Tryptophan can also be produced by E. coli using enzymes that are expressed by five different genes. Next to these five genes are in what is called the tryptophan (trp) operon

02

The explanation for the answer

The cell must constantly have tryptophan on hand because it is an amino acid that is necessary for the creation of proteins. However, if there is already an abundance of tryptophan, producing more would be inefficient, and the trp receptor's expression would be suppressed. Lactose, a milk sugar, is not always accessible. The lac operon is only activated when lactose is present since it makes no sense to produce the enzymes required to digest an energy source that is not there.

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