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Chapter 14: Problem 22

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?

Short Answer

Expert verified
Both lac and trp repressors bind to their respective operator sites and prevent transcription under certain conditions. However, lac repressor binds when lactose is absent while trp repressor binds when tryptophan is abundant. Small effector molecules like allolactose and tryptophan influence the binding dynamics of these repressors respectively.

Step by step solution

01

Lac Repressor and Operator Site Binding

The lac repressor protein binds to the lac operator site when lactose is not present in the cell, preventing the transcription of the lac operon.
02

Trp Repressor and Operator Site Binding

The trp repressor protein, on the other hand, binds to the trp operator site when tryptophan, an amino acid, is abundant in the cell, preventing the transcription of the trp operon.
03

Lac Repressor and Transcription

In terms of effects on transcription, when lactose is present in the cell, it binds to the lac repressor protein, causing the protein to detach from the operator site, enabling the lac operon's transcription.
04

Trp Repressor and Transcription

In the case of the trp repressor, when tryptophan levels in the cell are low, the trp repressor detaches from the operator site, allowing the transcription of the trp operon.
05

Lac Repressor and Small Effector Molecules

Small effector molecules, specifically an isomer of lactose called allolactose, influences the lac repressor by binding to it when lactose is present, causing it to change shape and consequently detach from the operator site.
06

Trp Repressor and Small Effector Molecules

In the case of trp repressor, tryptophan itself acts as a small effector molecule that, when abundant, binds to the trp repressor protein causing it to change shape and bind to the operator site, preventing transcription.

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Most popular questions from this chapter

Transcriptional regulation often involves a regulatory protein that binds to a segment of DNA and a small effector molecule that binds to the regulatory protein. Do each of the following terms apply to a regulatory protein, a segment of DNA, or a small effector molecule? A. Repressor B. Inducer C. Operator site D. Corepressor E. Activator F. Attenuator G. Inhibitor

Transcriptional repressor proteins (e.g., lac repressor), antisense RNA, and feedback inhibition are three different mechanisms that turn off the expression of genes and gene products. Which of these three mechanisms will be most effective in each of the following situations? A. Shutting down the synthesis of a polypeptide B. Shutting down the synthesis of mRNA C. Shutting off the function of a protein For your answers to parts \(\mathrm{A}-\mathrm{C}\) that list more than one mechanism, which mechanism will be the fastest or the most efficient?

Translational control is usually aimed at preventing the initiation of translation. With regard to cellular efficiency, why do you think this is the case?

If an abnormal repressor protein could still bind allolactose but the binding of allolactose did not alter the conformation of the repressor protein, how would the expression of the lac operon be affected?

Some mutations have a cis-effect, whereas others have a transeffect. Explain the molecular differences between cis- and transmutations. Which type of mutation (cis or trans) can be complemented in a merozygote experiment?
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