In a typical lytic viral infection, which event marks the conclusion of the lytic cycle in the host cell?

Introduction / Context:
Viruses can follow different life cycles when they infect host cells. Two classic patterns described in textbooks are the lytic cycle and the lysogenic cycle. The lytic cycle is characterised by rapid replication of the virus and destruction of the host cell. This question asks you to identify the event that marks the conclusion of a typical lytic infection, that is, the final step of the lytic cycle inside a host cell.

Given Data / Assumptions:

• The topic is the lytic infection cycle of a virus, such as a bacteriophage infecting bacteria.

• Several stages of viral activity are mentioned: messenger RNA production, DNA integration, prophage formation, and host cell bursting.

• You are to select the event that specifically concludes the lytic cycle.

• The difference between lytic and lysogenic cycles is assumed knowledge.

Concept / Approach:
In the lytic cycle, a virus attaches to a host, injects its nucleic acid, takes over the host machinery to make viral components, assembles new virus particles, and finally causes the host cell to lyse, releasing many new virions. By contrast, in the lysogenic cycle the viral genome may integrate into the host DNA as a prophage and remain dormant for a time. Therefore, integration and prophage formation correspond to lysogeny, not the terminal step of lysis. The last step of a lytic infection is the bursting of the host cell, which releases the newly formed viruses to infect other cells.

Step-by-Step Solution:
Step 1: Recall that after entry into the cell, viral DNA or RNA is expressed to produce viral messenger RNA. Step 2: This viral messenger RNA directs synthesis of viral proteins and replication of viral nucleic acid. Step 3: Newly synthesized viral components are assembled into complete virus particles inside the host cell. Step 4: In the purely lytic pathway, the virus does not integrate permanently into the host DNA; instead, it proceeds to lyse the cell. Step 5: The final hallmark of a lytic infection is the bursting or lysis of the host cell, which releases many new virions into the surrounding environment. Step 6: Production of a prophage and embedding of viral DNA into host DNA are key features of a lysogenic cycle, not the terminal step of a lytic cycle. Step 7: Therefore, the concluding event of a lytic infection is host cell lysis with release of new viral particles.

Verification / Alternative check:
Diagrams of the bacteriophage life cycle in microbiology textbooks show a sequence of steps labelled adsorption, penetration, biosynthesis, maturation, and lysis. The last panel typically illustrates the host cell bursting, with many phage particles emerging. A separate diagram for lysogeny shows viral DNA integrated as a prophage, persisting through host cell divisions without immediate lysis. These illustrations confirm that cell lysis is the endpoint of the lytic cycle, while integration and prophage formation belong to the lysogenic cycle.

Why Other Options Are Wrong:

Production of a prophage: This is a feature of the lysogenic cycle where viral DNA integrates into the host genome and remains latent.

Production of viral messenger RNA: This is an early step in both lytic and lysogenic infections but not the final step of the lytic cycle.

Embedding of viral DNA into host DNA: Again, this is characteristic of lysogeny, not the endpoint of a lytic infection.

Transformation back into a normal cell: This does not describe viral replication; lytic infection ends in destruction, not healing.

Common Pitfalls:
A common mistake is confusing the lysogenic and lytic cycles, especially when similar terms like prophage and viral DNA are used. Students may also think that DNA integration is always part of viral infection, forgetting that some viruses follow a purely lytic route. Another pitfall is ignoring the sequence of events and focusing only on individual terms. To avoid these errors, always link the word lytic with lysis, which literally means breaking or bursting of the cell.

Final Answer:
A lytic infection concludes with the bursting (lysis) of the host cell and the release of many new viral particles.