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

Previous problemNext problem

3:52 minutes

Problem 28e

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

Verified step by step guidance

Understand the context: The λ phage can enter either the lytic or lysogenic life cycle. The decision is regulated by a genetic switch involving key genes such as cII and cro. The cII gene promotes lysogeny, while the cro gene promotes the lytic cycle. Mutations in these genes can disrupt this balance.

Analyze the role of cII: The cII protein activates the transcription of genes required for lysogeny, such as the cI gene, which encodes the λ repressor. If cII is inactivated by mutation, the transcription of cI will be impaired, reducing the likelihood of lysogeny and favoring the lytic cycle.

Analyze the role of cro: The cro protein represses the transcription of the cI gene, thereby inhibiting lysogeny and promoting the lytic cycle. If cro is inactivated by mutation, the repression of cI will be lifted, allowing the λ repressor to accumulate and favor lysogeny over the lytic cycle.

Consider the combined effects: A mutation in cII would make it difficult for the phage to establish lysogeny, as the cI gene would not be activated. Conversely, a mutation in cro would make it difficult for the phage to enter the lytic cycle, as cI repression would be lost. The specific life cycle outcome depends on which gene is mutated and the environmental conditions.

Summarize the outcomes: Inactivation of cII skews the balance toward the lytic cycle, while inactivation of cro skews the balance toward lysogeny. These effects highlight the importance of the genetic switch in determining the phage's life cycle.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

Key Concepts

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

Lytic and Lysogenic Cycles

The lytic and lysogenic cycles are two distinct pathways that bacteriophages, like λ phage, can follow after infecting a host bacterium. In the lytic cycle, the phage replicates rapidly, leading to the destruction of the host cell and the release of new phage particles. In contrast, the lysogenic cycle involves the integration of the phage DNA into the host genome, allowing it to replicate along with the host cell without causing immediate harm.

cII Protein

The cII protein is a key regulatory protein in λ phage that promotes the lysogenic cycle. It activates the transcription of genes necessary for lysogeny, including the repressor protein cI, which maintains the phage in a dormant state within the host. If cII is inactivated by mutations, the phage is more likely to enter the lytic cycle due to the lack of lysogenic promotion.

cro Protein

The cro protein is another regulatory protein in λ phage that plays a crucial role in determining the lytic cycle. It represses the expression of the cI gene, thereby favoring the lytic pathway. Mutations that inactivate cro can lead to increased levels of cI, promoting lysogeny and preventing the lytic cycle, as the phage would be unable to effectively suppress the lysogenic state.

Watch next

Master Bacteriophage Life Cycle with a bite sized video explanation from Kylia

Start learning

Related Videos

Related Practice

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

393

views

Textbook Question

O_R3 mutation in λ phage

365

views

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.

305

views

Textbook Question