Chapter 20: Problem 16

Describe what occurs when bacteriophage \(\lambda\) invades an \(E .\) \(coli\) cell and establishes lysogeny. What would happen if the \(E .\) \(coli\) cell were exposed to a high dose of UV light?

Short Answer

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Answer: Upon exposure to a high dose of UV light, the E. coli cell's DNA becomes damaged, triggering its SOS response. This leads to the activation of the phage's excisionase enzyme, which frees the phage DNA from the host genome. Consequently, the lambda phage enters the lytic cycle, causing the production of new virus particles and eventually leading to the lysis of the E. coli cell.

Step by step solution

Lambda phage invasion of E. coli cell

Bacteriophage lambda (λ) is a virus that specifically infects E. coli bacteria. Infection begins when the virus attaches itself to the outer membrane of the E. coli cell using its tail fibers. It then injects its DNA into the host cell through a process called transduction.

Lysogenic and lytic pathways

Once inside the cell, the lambda phage DNA must decide whether to enter a lytic or lysogenic cycle. In the lytic cycle, the phage DNA replicates and directs the host cell to produce new virus particles, ultimately leading to cell lysis and the release of new phage particles. In the lysogenic cycle, the phage DNA integrates into the host cell's chromosome and remains dormant, allowing it to be replicated along with the host's genetic material when the cell divides.

Establishing lysogeny

Bacteriophage lambda establishes lysogeny by integrating its DNA into the E. coli chromosome at a specific attachment site, forming a prophage. The integration is mediated by lambda's integrase enzyme, which recombines the phage and host DNA. During lysogeny, most of the phage's genes are turned off, and the host cell continues to function and divide normally, carrying the prophage within its genome. The integrated lambda DNA can be stably maintained in the host for many generations without causing harm to the cell.

Induction of the lytic cycle

In response to specific environmental cues or stressors, such as exposure to UV light or certain chemicals, the lambda phage can switch from lysogeny to the lytic cycle. This process is called induction.

Exposure to UV light

If an E. coli cell containing the lambda prophage was exposed to a high dose of UV light, it would cause DNA damage, which would activate the host's SOS response - a global stress response to DNA damage. This response leads to the activation of phage's excisionase enzyme, which helps to excise the phage DNA from the host genome. Once the phage DNA is free from the host, it would enter the lytic cycle, leading to the production of new virus particles and eventual lysis of the E. coli cell.

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Describe what occurs when bacteriophage \(\lambda\) invades an \(E .\) \(coli\) cell and establishes lysogeny. What would happen if the \(E .\) \(coli\) cell were exposed to a high dose of UV light?

Short Answer

Step by step solution

Lambda phage invasion of E. coli cell

Lysogenic and lytic pathways

Establishing lysogeny

Induction of the lytic cycle

Exposure to UV light

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