Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 15: Problem 3

Describe which enzymes are required for lactose and tryptophan metabolism in bacteria when lactose and tryptophan, respectively, are (a) present and (b) absent.

Short Answer

Expert verified
Answer: (a) In the presence of lactose, beta-galactosidase is produced, and in the presence of tryptophan, tryptophanase production is inhibited. (b) In the absence of lactose, beta-galactosidase production is inhibited, while in the absence of tryptophan, production of tryptophanase occurs, allowing for tryptophan metabolism.

Step by step solution

01

Lactose Metabolism Enzymes and Regulation

Bacteria, such as Escherichia coli (E. coli), metabolize lactose using the enzyme beta-galactosidase, which is encoded by the lacZ gene. The expression of this enzyme is regulated by the lac operon, a set of genes that are controlled by the lac repressor protein and catabolite activator protein (CAP).
02

Lactose Metabolism in the Presence of Lactose

When lactose is present, the lac repressor protein releases from the lac operon, allowing the transcription of lacZ, lacY, and lacA. This leads to the production of beta-galactosidase (from lacZ), which is crucial for lactose metabolism, as it breaks lactose into glucose and galactose.
03

Lactose Metabolism in the Absence of Lactose

When lactose is absent, the lac repressor protein binds to the lac operon and prevents the transcription of lacZ, lacY, and lacA. This means that beta-galactosidase is not produced due to the lack of lactose. As a result, there's no lactose metabolism.
04

Tryptophan Metabolism Enzymes and Regulation

The metabolism of tryptophan is driven by the enzyme tryptophanase, encoded by the tna gene. The expression of tryptophanase is regulated by the tryptophanase operon (tna operon) in bacteria such as E. coli. The tna operon is controlled by the tryptophan repressor protein (TrpR) and other regulatory elements.
05

Tryptophan Metabolism in the Presence of Tryptophan

When tryptophan is present, it acts as a corepressor by binding to the TrpR protein, which then becomes capable of binding to the tna operon. This prevents the transcription of the tna gene and subsequent production of tryptophanase. As a result, tryptophan is not metabolized.
06

Tryptophan Metabolism in the Absence of Tryptophan

In the absence of tryptophan, the TrpR protein is unable to bind to the tna operon, allowing the transcription of the tna gene. This leads to the production of tryptophanase, which is responsible for the catabolism of tryptophan into indole, pyruvate, and ammonia. To summarize, the enzymatic responses to lactose and tryptophan are as follows: (a) In the presence of lactose, beta-galactosidase is produced, and in the presence of tryptophan, tryptophanase production is inhibited. (b) In the absence of lactose, beta-galactosidase production is inhibited, while in the absence of tryptophan, production of tryptophanase occurs, allowing for tryptophan metabolism.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

What is RNA-induced gene silencing in eukaryotes? How do sncRNAs affect gene regulation and how are they currently used in research and medicine?

What are the subcategories within eukaryotic promoters? How do enhancers and silencers differ from promoters?

A bacterial operon is responsible for production of the biosynthetic enzymes needed to make the theoretical amino acid tisophane (tis). The operon is regulated by a separate gene, \(R,\) deletion of which causes the loss of enzyme synthesis. In the wild-type condition, when tis is present, no enzymes are made; in the absence of tis, the enzymes are made. Mutations in the operator gene \(\left(O^{-}\right)\) result in repression regardless of the presence of tis. Is the operon under positive or negative control? Propose a model for (a) repression of the genes in the presence of tis in wild-type cells and (b) the mutations.

Both attenuation and riboswitches rely on changes in the secondary structure of the leader regions of mRNA to regulate gene expression. Compare and contrast the specific mechanisms in these two types of regulation.

Contrast positive versus negative regulation of gene expression. Describe the role of the repressor in an inducible system and in a repressible system.
See all solutions

Recommended explanations on Biology Textbooks

Microbiology

Read Explanation

Cell Cycle

Read Explanation

Biology Experiments

Read Explanation

Biological Molecules

Read Explanation

Genetic Information

Read Explanation

Ecological Levels

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free