Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

12. Gene Regulation in Prokaryotes

Lac Operon

Genetics

12. Gene Regulation in Prokaryotes

Lac Operon

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2:44 minutes

Problem 16a

Textbook Question

In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?
Mutation of consensus sequence in the lac promoter

Verified step by step guidance

Understand the role of the lac operon: The lac operon is a set of genes in E. coli that are involved in lactose metabolism. It is regulated by the promoter, operator, and regulatory proteins. The promoter is the site where RNA polymerase binds to initiate transcription.

Define the consensus sequence: The consensus sequence in the lac promoter is a specific DNA sequence that RNA polymerase recognizes and binds to. Mutations in this sequence can affect the binding efficiency of RNA polymerase.

Analyze the effect of the mutation: A mutation in the consensus sequence of the lac promoter is likely to reduce or eliminate the ability of RNA polymerase to bind to the promoter. This would decrease or prevent transcription of the operon genes (lacZ, lacY, and lacA).

Consider the impact on gene expression: If RNA polymerase cannot bind effectively, the operon genes will not be transcribed, even in the presence of lactose. This means the enzymes required for lactose metabolism will not be produced.

Summarize the outcome: The mutation in the consensus sequence of the lac promoter would likely result in a significant reduction or complete loss of operon gene transcription, leading to an inability of the cell to metabolize lactose efficiently.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Lac Operon Structure

The lac operon is a set of genes in E. coli that are involved in the metabolism of lactose. It consists of three structural genes (lacZ, lacY, and lacA) and regulatory elements, including a promoter and an operator. The operon is activated in the presence of lactose and repressed when glucose is available, illustrating the principles of gene regulation in prokaryotes.

Promoter Consensus Sequence

The promoter consensus sequence is a specific DNA sequence recognized by RNA polymerase and transcription factors to initiate transcription. Mutations in this sequence can significantly affect the binding efficiency of RNA polymerase, leading to altered levels of gene expression. In the context of the lac operon, changes in the promoter can disrupt the transcription of the operon genes.

Transcription Regulation

Transcription regulation refers to the mechanisms that control the rate of gene transcription. In the lac operon, this regulation is achieved through the binding of repressor proteins and the availability of inducers like allolactose. Mutations affecting the promoter can lead to either increased or decreased transcription, depending on how they influence the binding of regulatory proteins and RNA polymerase.

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In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?

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In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?

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In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?

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Textbook Question

In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?

Mutation of the repressor binding site on the operator sequence

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Textbook Question

Identify which of the following lac operon haploid genotypes transcribe operon genes inducibly and which transcribe genes constitutively. Indicate whether the strain is lac⁺ (able to grow on lactose-only medium) or lac⁻ (cannot grow on lactose medium).

I⁺ P⁺ Oᶜ Z⁺ Y⁺

I⁺ P⁺ Oᶜ Z⁺ Y⁻

I⁺ P⁺ O⁺ Z⁻ Y⁺