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

Lambda Bacteriophage and Life Cycle Regulation

Genetics

12. Gene Regulation in Prokaryotes

Lambda Bacteriophage and Life Cycle Regulation

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2:55 minutes

Problem 26b

Textbook Question

Suppose that base substitution mutations sufficient to eliminate the function of the operator regions listed below were to occur. For each case, describe how transcription or life cycle would be affected.
O_R1 mutation in λ phage

Verified step by step guidance

Understand the context: The λ phage is a bacteriophage that can switch between the lytic and lysogenic life cycles. The operator regions (OR1, OR2, OR3) are DNA sequences where regulatory proteins bind to control transcription of genes involved in these life cycles.

Identify the role of OR1: OR1 is a binding site for the λ repressor protein (CI). When CI binds to OR1, it represses the transcription of the cro gene, which is essential for the lytic cycle. This helps maintain the lysogenic state.

Analyze the mutation: A mutation in OR1 that eliminates its function would prevent the λ repressor protein from binding to this site. Without CI binding to OR1, the cro gene would not be repressed.

Predict the effect on transcription: Since the cro gene is not repressed, its transcription would increase. The Cro protein promotes the lytic cycle by repressing the synthesis of the λ repressor (CI), leading to a shift toward the lytic life cycle.

Summarize the life cycle impact: The mutation in OR1 would disrupt the balance between the lytic and lysogenic cycles, favoring the lytic cycle. This means the phage would likely enter the lytic cycle, leading to the destruction of the host cell and the production of new phage particles.

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Key Concepts

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

Operator Regions

Operator regions are specific DNA sequences where regulatory proteins bind to control the transcription of adjacent genes. In the context of phages like λ phage, these regions play a crucial role in determining whether the phage enters a lytic or lysogenic cycle, influencing gene expression and viral replication.

Transcription Regulation

Transcription regulation refers to the mechanisms that control the rate and timing of gene expression. In λ phage, the operator region interacts with repressor proteins, which can inhibit or promote transcription based on environmental signals, thus affecting the phage's life cycle and its ability to produce new virions.

Lytic vs. Lysogenic Cycle

The lytic and lysogenic cycles are two distinct pathways that a bacteriophage can follow after infecting a host. In the lytic cycle, the phage replicates rapidly, leading to cell lysis and release of new phage particles, while in the lysogenic cycle, the phage integrates its DNA into the host genome, remaining dormant until conditions trigger its reactivation.

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Related Practice

Multiple Choice

The N protein is an anti-terminator. What does this mean?

Which of the following proteins is mainly responsible for entering the bacteriophage into the lysogenic cycle?

Describe the difference between the bacteriophage lytic cycle and lysogenic cycle.

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Textbook Question

Describe the lytic and lysogenic life cycles of λ bacteriophage. What roles do λ repressor and Cro protein play in controlling transcription from P_R and P_RM, and how are these roles linked to lysis and lysogeny?

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Textbook Question

Suppose that base substitution mutations sufficient to eliminate the function of the operator regions listed below were to occur. For each case, describe how transcription or life cycle would be affected.

O_R3 mutation in λ phage

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Textbook Question

Two different mutations affect P_RE. Mutant 1 decreases transcription from the promoter to 10% of normal. Mutant 2 increases transcription from the promoter to 10 times greater than the wild type. How will each mutation affect the determination of the lytic or lysogenic life cycle in mutant λ phage strains? Explain your answers.

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Textbook Question

How would mutations that inactivate each of the following genes affect the determination of the lytic or lysogenic life cycle in mutated λ phage strains? Explain your answers.

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Textbook Question

How would mutations that inactivate each of the following genes affect the determination of the lytic or lysogenic life cycle in mutated λ phage strains? Explain your answers.

cII and cro

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