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

13. Gene Regulation in Eukaryotes

GAL Regulation

Genetics

13. Gene Regulation in Eukaryotes

GAL Regulation

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0:58 minutes

Problem 25c

Textbook Question

Regulation of the lac operon in E. coli and regulation of the GAL system in yeast are analogous in that they both serve to adapt cells to growth on different carbon sources. However, the transcriptional changes are accomplished very differently. Consider the conceptual similarities and differences as you address the following.
Compare and contrast how these two systems are negatively regulated such that they are downregulated in the presence of glucose.

Verified step by step guidance

Step 1: Begin by defining the lac operon and the GAL system, emphasizing that both are gene regulatory systems that enable cells to utilize alternative carbon sources when glucose is scarce.

Step 2: Explain negative regulation in the lac operon, focusing on the role of the lac repressor protein, which binds to the operator region to block transcription in the absence of lactose, and how glucose presence leads to catabolite repression via low cAMP levels, reducing activation by CAP-cAMP complex.

Step 3: Describe negative regulation in the GAL system, highlighting the role of the Gal80 protein as a repressor that inhibits the activator Gal4 in the absence of galactose, and how glucose presence represses GAL gene expression through a different mechanism involving Mig1, a glucose-responsive repressor that binds to the promoters of GAL genes to inhibit transcription.

Step 4: Compare the two systems by noting that both use repressors to downregulate gene expression in the presence of glucose, but the lac operon primarily uses catabolite repression affecting activator binding, while the GAL system uses a dedicated glucose-responsive repressor protein (Mig1) to directly inhibit transcription.

Step 5: Summarize the conceptual difference that the lac operon repression is largely indirect via modulation of activator availability (CAP-cAMP), whereas the GAL system repression involves direct binding of a glucose-activated repressor to the DNA, illustrating different molecular strategies to achieve similar regulatory outcomes.

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Key Concepts

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

Negative Regulation of the lac Operon

The lac operon in E. coli is negatively regulated by the lac repressor protein, which binds to the operator region to block transcription when lactose is absent. In the presence of glucose, catabolite repression occurs via low cAMP levels, preventing activation by CAP, thus downregulating the operon. This dual control ensures the operon is off when glucose is available, prioritizing its use over lactose.

Negative Regulation of the GAL System in Yeast

The GAL system in yeast is negatively regulated primarily by the Gal80 protein, which inhibits the activator Gal4 in the absence of galactose. When glucose is present, repression occurs through Mig1, a glucose-responsive repressor that binds to the GAL gene promoters, recruiting corepressors to inhibit transcription. This mechanism ensures GAL genes are repressed when glucose is the preferred carbon source.

Conceptual Similarities and Differences in Glucose-Mediated Repression

Both systems downregulate gene expression in the presence of glucose to prioritize its metabolism, demonstrating catabolite repression. However, the lac operon uses a combination of repressor binding and activator absence (via cAMP-CAP), while the GAL system employs a dedicated glucose-responsive repressor (Mig1). Thus, both achieve similar outcomes through distinct molecular mechanisms.

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Textbook Question

Explain how the following mutations would affect transcription of the yeast GAL1 gene in the presence of galactose.

A mutation within the GAL80 gene that blocks the ability of Gal80 protein to interact with Gal3p.

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Textbook Question

Explain how the following mutations would affect transcription of the yeast GAL1 gene in the presence of galactose.

A point mutation in the GAL1 core promoter that alters the sequence of the TATA box.

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Textbook Question

Explain how the following mutations would affect transcription of the yeast GAL1 gene in the presence of galactose.

A deletion within the GAL4 gene that removes the region encoding amino acids 1 to 100.

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Textbook Question

Explain how the following mutations would affect transcription of the yeast GAL1 gene in the presence of galactose.

A deletion of the entire GAL3 gene.

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Textbook Question

Regulation of the lac operon in E. coli and regulation of the GAL system in yeast are analogous in that they both serve to adapt cells to growth on different carbon sources. However, the transcriptional changes are accomplished very differently. Consider the conceptual similarities and differences as you address the following.

Compare and contrast the cis-regulatory elements of the lac operon and GAL gene system.

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Textbook Question

Regulation of the lac operon in E. coli and regulation of the GAL system in yeast are analogous in that they both serve to adapt cells to growth on different carbon sources. However, the transcriptional changes are accomplished very differently. Consider the conceptual similarities and differences as you address the following.

Compare and contrast the roles of the lac operon inducer in bacteria and Gal3p in eukaryotes in the regulation of their respective systems.

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Multiple Choice

Which of the following statements is accurate regarding the regulation of gal genes in yeast?

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Multiple Choice

Which of the following is the purpose of the GAL gene system?