Understanding Viral Infection Sequence in Macrophages

This question asks us to arrange the events that occur when a virus infects macrophages in the correct order. The events described involve viral entry, processing of genetic material using reverse transcriptase, integration into the host genome, and production of new viruses. This sequence is characteristic of retroviruses, such as HIV, which are known to infect macrophages.

Analyzing the Stages of Viral Infection

Let's break down the given events and determine their logical order in the context of a viral infection:

• (A) Virus infects macrophages: This is the very first step. The virus must first attach to and enter the macrophage cell.
• (D) Viral RNA is introduced into macrophages: Once the virus has entered the cell, its genetic material is released into the cytoplasm. For many viruses, especially retroviruses which use reverse transcriptase, this genetic material is RNA. This step happens inside the cell after entry.
• (B) Viral DNA is produced by reverse transcriptase: Retroviruses carry an enzyme called reverse transcriptase. After the viral RNA is released into the cytoplasm, this enzyme uses the viral RNA as a template to synthesize a complementary strand of DNA, and then a second strand to form double-stranded viral DNA. This step occurs after the RNA is introduced.
• (C) Viral DNA incorporates into the host genome: The double-stranded viral DNA produced by reverse transcriptase then moves into the cell's nucleus. Here, another viral enzyme, integrase, helps the viral DNA insert itself into the host cell's own DNA (genome). This integrated viral DNA is called a provirus. This step happens after the viral DNA is created.
• (E) New viruses are produced: Once the viral DNA is integrated into the host genome, the host cell's machinery is used to transcribe the provirus into viral RNA and translate it into viral proteins. These components are then assembled into new virus particles, which can bud off from the cell membrane to infect other cells. This is the final stage of the replication cycle.

Sequencing the Viral Infection Steps

Based on the analysis above, the events occur in the following order:

1. The virus infects the macrophage (A).
2. Viral RNA is introduced into the macrophage (D).
3. Viral DNA is produced from the RNA using reverse transcriptase (B).
4. The viral DNA incorporates into the host cell's genome (C).
5. New viruses are produced and released (E).

This gives us the sequence: (A), (D), (B), (C), (E).

Summary Table of Viral Infection Sequence

Comparing this sequence to the given options, we find that the sequence (A), (D), (B), (C), (E) matches one of the choices.

Revision Table: Key Concepts in Viral Infection

Additional Information: Retroviral Life Cycle Details

The sequence described in the question is typical of the retroviral life cycle. After integration, the provirus can remain dormant for a period, or it can be transcribed by the host cell's machinery to produce new viral RNA and proteins. This new viral RNA serves two purposes: some are packaged as genomes for new virions, and others are translated into viral proteins (like enzymes and structural proteins).

Macrophages are important target cells for certain retroviruses, such as HIV. They act as reservoirs for the virus and can transport it to different parts of the body. Understanding this specific sequence of events is crucial for developing treatments and therapies against such viral infections.