NExt microbiology: bacteriophage Life cycle
The lambda (λ) phase of a bacteriophage refers to the lysogenic phase in the life cycle of the bacteriophage lambda. Bacteriophage lambda, also known as λ phage, is a type of virus that infects Escherichia coli (E. coli) bacteria. The lambda phage can follow two distinct life cycles: the lysogenic cycle and the lytic cycle. The lambda phase corresponds to the lysogenic cycle of the λ phage.
**Key Points about the Lambda Phase (Lysogenic Cycle):**
1. **Lysogenic Cycle:** During the lambda phase, the bacteriophage lambda enters a lysogenic cycle. In this cycle, the phage DNA becomes integrated into the bacterial host's chromosome.
2. **Prophage Formation:** The phage DNA integrated into the bacterial chromosome is called a prophage. The bacterial host containing the integrated phage DNA is referred to as a lysogen.
3. **Repressor Protein:** Once integrated, the prophage produces a repressor protein that prevents the expression of viral genes. This helps maintain a dormant state, allowing the bacterial host to replicate and divide normally.
4. **Cell Division:** As the bacterial host divides, the integrated prophage is also replicated and passed on to daughter cells. This is achieved through the replication of the host chromosome, including the integrated phage DNA.
5. **Induction:** Under certain conditions, such as DNA damage or stress, the prophage can be induced to leave the bacterial chromosome and enter the lytic cycle. This transition from the lysogenic cycle to the lytic cycle is called induction.
6. **Lytic Cycle Activation:** Upon induction, the repressor protein is inactivated or degraded. This leads to the expression of viral genes and the initiation of the lytic cycle, during which new phage particles are produced and released from the bacterial cell through lysis.
7. **Impact:** The lysogenic cycle allows the bacteriophage lambda to persist within the bacterial host over extended periods without causing immediate cell death. This can contribute to horizontal gene transfer and the spread of phage DNA in bacterial populations.
The lambda phase of the bacteriophage lambda is an example of how viruses can establish a stable relationship with their host by integrating their genetic material into the host's genome. This integration enables the virus to replicate along with the host, while also having the potential to switch to the lytic cycle under appropriate conditions.
Certainly, here are 10 multiple-choice questions (MCQs) related to the lambda phase of the bacteriophage and its lysogenic cycle, along with their answers:
1. **Q: The lambda phase of a bacteriophage refers to:**
- A) The lytic phase
- B) The dormant phase
- C) The prophage formation phase
- D) The replication phase
- **Answer: C) The prophage formation phase**
2. **Q: What is the term for the integrated phage DNA within the bacterial host's chromosome during the lambda phase?**
- A) Repressor
- B) Lytic DNA
- C) Prophage
- D) Inducer
- **Answer: C) Prophage**
3. **Q: During the lambda phase, the phage DNA becomes integrated into the:**
- A) Bacterial cell wall
- B) Bacterial cytoplasm
- C) Bacterial ribosome
- D) Bacterial chromosome
- **Answer: D) Bacterial chromosome**
4. **Q: Which protein prevents the expression of viral genes and maintains a dormant state during the lambda phase?**
- A) Repressor protein
- B) Inducer protein
- C) Lysozyme protein
- D) Capsid protein
- **Answer: A) Repressor protein**
5. **Q: What is the term for a bacterial host containing the integrated phage DNA during the lambda phase?**
- A) Lysogen
- B) Lytic cell
- C) Prophage cell
- D) Repressor cell
- **Answer: A) Lysogen**
6. **Q: Under what conditions is the prophage induced to leave the bacterial chromosome and enter the lytic cycle?**
- A) When the bacterial cell divides
- B) During normal growth and replication
- C) In response to nutrient availability
- D) Under DNA damage or stress conditions
- **Answer: D) Under DNA damage or stress conditions**
7. **Q: What occurs during induction in the lambda life cycle?**
- A) Repressor protein is synthesized
- B) Prophage DNA integrates into the host chromosome
- C) Lysis of bacterial cells
- D) Prophage leaves the bacterial chromosome
- **Answer: D) Prophage leaves the bacterial chromosome**
8. **Q: The lambda phase is associated with which type of cycle in the bacteriophage lambda life cycle?**
- A) Lytic cycle
- B) Replication cycle
- C) Lysogenic cycle
- D) Metabolic cycle
- **Answer: C) Lysogenic cycle**
9. **Q: The repressor protein produced during the lambda phase directly interacts with:**
- A) Bacterial ribosomes
- B) Phage DNA
- C) Capsid proteins
- D) Inducer molecules
- **Answer: B) Phage DNA**
10. **Q: What is the main advantage of the lambda phase for the bacteriophage lambda?**
- A) Rapid host cell lysis
- B) Enhanced viral replication
- C) Horizontal gene transfer and persistence
- D) Prevention of bacterial cell division
- **Answer: C) Horizontal gene transfer and persistence**
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