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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2:46 minutes

Problem 9

Textbook Question

What role does cAMP play in transcription of lac operon genes? What role does CAP play in transcription of lac operon genes?

Verified step by step guidance

Understand the lac operon: The lac operon is a set of genes in E. coli that are involved in the metabolism of lactose. It is regulated by the presence or absence of lactose and glucose in the environment.

Explain the role of cAMP: Cyclic AMP (cAMP) is a signaling molecule that accumulates in the cell when glucose levels are low. It acts as a signal to indicate that the cell needs to utilize alternative energy sources, such as lactose.

Describe the interaction between cAMP and CAP: cAMP binds to the Catabolite Activator Protein (CAP), forming a cAMP-CAP complex. This complex is essential for the activation of the lac operon.

Explain the role of CAP: CAP, when bound to cAMP, binds to a specific site near the promoter of the lac operon. This binding enhances the ability of RNA polymerase to attach to the promoter, thereby increasing the transcription of the lac operon genes.

Summarize the relationship: In summary, cAMP signals low glucose levels, and the cAMP-CAP complex facilitates the transcription of the lac operon genes by enhancing RNA polymerase binding. This ensures that the cell can metabolize lactose when glucose is scarce.

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Key Concepts

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

cAMP (cyclic Adenosine Monophosphate)

cAMP is a secondary messenger important in cellular signaling. In the context of the lac operon, cAMP levels increase when glucose is scarce, leading to the activation of the transcription of genes responsible for lactose metabolism. It binds to the CAP protein, facilitating the recruitment of RNA polymerase to the promoter region of the lac operon.

CAP (Catabolite Activator Protein)

CAP is a transcriptional activator that enhances the expression of the lac operon in the presence of cAMP. When cAMP binds to CAP, the complex binds to the promoter region of the lac operon, promoting the binding of RNA polymerase and thus increasing transcription of the operon genes. This mechanism ensures that the cell efficiently utilizes available energy sources.

lac Operon

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 is regulated by the presence of lactose and glucose. The operon is an example of gene regulation, where the presence of lactose induces transcription, while glucose availability inhibits it through catabolite repression.

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Related Practice

Textbook Question

For the genotypes and conditions (lactose present or absent) shown in the following table, predict whether functional enzymes, nonfunctional enzymes, or no enzymes are made.

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Textbook Question

The locations of numerous lacI⁻ and lacIˢ mutations have been determined within the DNA sequence of the lacI gene. Among these, lacI⁻ mutations were found to occur in the 5′-upstream region of the gene, while lacIˢ mutations were found to occur farther downstream in the gene. Are the locations of the two types of mutations within the gene consistent with what is known about the function of the repressor that is the product of the lacI gene?

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Textbook Question

The CAP binding site in the lac promoter is the location of positive regulation of gene expression for the operon. Identify what binds at this site to produce positive regulation, under what circumstances binding occurs, and how binding exerts a positive effect.

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Textbook Question

Describe the experimental rationale that allowed the lac repressor to be isolated.

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Textbook Question

What properties demonstrate that the lac repressor is a protein? Describe the evidence that it indeed serves as a repressor within the operon system.

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Textbook Question

How would a cap⁻ mutation that produces an inactive CAP protein affect transcriptional control of the lac operon?

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Textbook Question

Predict the effect on the inducibility of the lac operon of a mutation that disrupts the function of:

(a) The CRP gene, which encodes the CAP protein

(b) The CAP-binding site within the promoter.

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Textbook Question

Erythritol, a natural sugar abundant in fruits and fermenting foods, is about 65 percent as sweet as table sugar and has about 95 percent fewer calories. It is 'tooth friendly' and generally devoid of negative side effects as a human consumable product. Pathogenic Brucella strains that catabolize erythritol contain four closely spaced genes, all involved in erythritol metabolism. One of the four genes (eryD) encodes a product that represses the expression of the other three genes. Erythritol catabolism is stimulated by erythritol. Present a simple regulatory model to account for the regulation of erythritol catabolism in Brucella. Does this system appear to be under inducible or repressible control?

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