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Chapter 14: Problem 8

In the lac operon, how would gene expression be affected if each one of the following segments was missing? A. lac operon promoter B. Operator site C. lacA gene

Short Answer

Expert verified
Gene expression would be significantly affected if any of these segments were missing: absence of the lac operon promoter would stop the transcription of the lac operon; absence of the operator site would lead to continual, unrestricted expression of the lac operon genes; absence of the lacA gene would slightly reduce the efficiency of lactose metabolism but have a minimal effect on gene regulation within the lac operon system.

Step by step solution

01

Understanding the lac operon system

The lac operon system, composed of the lac promoter, operator site, three structural genes (lacZ, lacY, and lacA), and a repressor gene, is a fundamental model in genetics for understanding gene regulation. The promoter region is where RNA polymerase binds to start transcription. The operator site is a DNA region where the repressor protein binds to prevent RNA polymerase from starting transcription. The lacA gene is one of the three structural genes and encodes the enzyme thiogalactoside transacetylase.
02

Assessing the effect of missing lac operon promoter

A missing lac operon promoter would halt the binding of RNA polymerase to the DNA, as the promoter region is crucial for transcription initiation. Consequently, transcription would not occur, leading to no expression of the lac operon genes.
03

Assessing the effect of missing operator site

If the operator site is missing, the lac repressor protein would have nowhere to bind, which would prevent it from blocking RNA polymerase. This could result in continuous transcription and expression of the lac operon genes, even when unneeded, as the mechanism to prevent unnecessary gene expression (i.e., the repressor protein binding to the operator site) would be gone.
04

Assessing the effect of missing lacA gene

A missing lacA gene would result in the loss of thiogalactoside transacetylase. Although this enzyme is not as crucial for lactose metabolism as the other two enzymes encoded by the lac operon (尾-galactosidase and lactose permease), its absence might still affect the efficiency of lactose metabolism. However, the precise impact on gene expression would likely be minimal, as the lacA gene is not involved in the regulation of the lac operon system.

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Most popular questions from this chapter

An operon is repressible-a small effector molecule turns off its transcription. Which combination(s) of small effector molecule and regulatory protein could be involved in this process? A. An inducer plus a repressor B. A corepressor plus a repressor C. An inhibitor plus an activator D. An inducer plus an activator

How are the actions of lac repressor and trp repressor similar and how are they different with regard to their binding to operator sites, their effects on transcription, and the influences of small effector molecules?

As described in Chapter 13, enzymes known as aminoacyl-tRNA synthetases are responsible for attaching amino acids to tRNAs. Let's suppose that in a mutant bacterium tryptophanyl-tRNA synthetase has a reduced ability to attach tryptophan to tRNA: its activity is only \(10 \%\) of that found in a normal bacterium. How would attenuation of the \(\operatorname{trp}\) operon be affected? Would the operon be more or less likely to be attenuated? Explain your answer.

A species of bacteria can synthesize the amino acid histidine, so they do not require histidine in their growth medium. A key enzyme, which we will call histidine synthetase, is necessary for histidine biosynthesis. When these bacteria are given histidine in their growth medium, they stop synthesizing histidine intracellularly. Based on this observation alone, propose three different regulatory mechanisms to explain why histidine biosynthesis ceases when histidine is in the growth medium. To explore this phenomenon further, you measure the amount of intracellular histidine synthetase protein when cells are grown in the presence and absence of histidine. In both conditions, the amount of this protein is identical. Which mechanism of regulation is consistent with this observation?

What is diauxic growth? Explain the roles of cAMP and CAP in this process.
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