Chapter 28, Problem 1P

(a)

Summary Introduction

To explain:

The changes in tryptophan synthase activity when the $\text{trp}\text{mRNA}$ is stable.

Introduction:

A group of prokaryotic genes with related functions that are regulated as a single unit, along with the control sequence that performs this regulation, is called an operon. Trp-operon have structural gene E, D, C, B and A that are repressed or inactive in the presence of tryptophan.

Explanation of Solution

Explanation:

There are one or more regulatory gene outside of the operon that produce trans acting factor such as repressor or activators. The trp operon is a repressible operon, which repress the expression of structural gene in the presences of tryptophan.

The $\text{trp}\text{mRNA}$ is stable in bacterial cell, even when the tryptophan is present in a medium, producing tryptophan synthase, thus the level of tryptophan synthase enzyme will remain high.

Conclusion

Conclusion:

The level of tryptophan synthase activity will remain high in the bacterial cell, when the $trp\text{mRNA}$ is stable

(b)

Summary Introduction

To explain:

The changes in tryptophan synthase activity when the $trp\text{mRNA}$ is degraded rapidly, but tryptophan synthase is stable.

Introduction:

A group of prokaryotic genes with related functions that are regulated as a single unit, along with the control sequence that performs this regulation, is called an operon. Trp-operon have structural gene E, D, C, B and A that are repressed or inactive in the presence of tryptophan.

Explanation of Solution

Explanation:

The $trpA$ and $trpB$ genes encodes the enzyme tryptophan synthase, in absence of tryptophan in the growth medium. If the $trp\text{mRNA}$ is degraded but the tryptophan synthase is stable, the activity of the enzyme will remain high, even in the presence of tryptophan.

(c)

Summary Introduction

To explain:

The changes in tryptophan synthase activity when the $trp\text{mRNA}$ and tryptophan synthase both are degraded rapidly.

Introduction:

A group of prokaryotic genes with related functions that are regulated as a single unit, along with the control sequence that performs this regulation, is called an operon. Trp-operon have structural gene E, D, C, B and A that are repressed or inactive in the presence of tryptophan.

Explanation of Solution

Explanation:

An operator is a DNA segment that turns the gene on and off. Its interaction with proteins increases or decrease the rate of transcription from occurring thus make an operon inducible or repressible.

Trp operon is a repressible operon which, repress the transcription of structural gene in the presence of tryptophan. The $\text{trp}\text{A}$ and $trpB$ genes encodes the $trp\text{mRNA}$ which produce enzyme tryptophan synthase. When the $trp\text{mRNA}$ and tryptophan synthase both are degraded rapidly it prevent the transcription of structural gene by decreasing the enzymatic activity.

Conclusion

Conclusion:

The tryptophan synthase activity will decrease when the $trp\text{mRNA}$ and tryptophan synthase are both degraded rapidly.