HIV Replication Cycle
எச்.ஐ.வி பெருக்க சுழற்சி
HIV is not just a virus; it is a master of genetic subversion. It forces the host cell to rewrite its own DNA to serve the pathogen. If you think this is simple infection, you are failing the NEET biology section.
The idea
HIV enters the macrophage and its RNA genome is converted into viral DNA by the enzyme reverse transcriptase. This viral DNA integrates into the host cell's genome, directing the cell to produce viral components. The macrophage continues to replicate the virus, effectively functioning as an HIV factory. Eventually, the virus spreads to helper T-lymphocytes, causing a massive decline in immunity.
Why it matters
Retroviruses use this mechanism to integrate their genetic material into the host genome, ensuring the virus persists and replicates indefinitely within the host.
NEET lens
NEET focuses on the enzyme 'reverse transcriptase' and the role of macrophages as the first factory. Do not confuse the sequence: RNA to DNA (Reverse Transcription) is the critical step. Remember, the virus replicates inside the macrophage, but the clinical crisis peaks when T-lymphocytes are destroyed. Expect questions on the order of viral replication steps.
Clinical significance
The destruction of helper T-lymphocytes leads to Acquired Immuno Deficiency Syndrome (AIDS). Without these cells, the body loses its ability to fight even minor opportunistic infections like Mycobacterium or Toxoplasma. The immune system effectively collapses.
Introduction
HIV (human immunodeficiency virus) is a retrovirus with an RNA genome. Inside human cells it copies its RNA into DNA, inserts it into the host's DNA and makes new viruses.
Core concept
Steps (NCERT): (1) HIV enters the body and first into macrophages. (2) Its RNA genome replicates to form viral DNA with the help of the enzyme reverse transcriptase. (3) The viral DNA gets incorporated into the host cell's DNA and directs the infected cell to produce virus particles; macrophages continue producing virus and act like an HIV factory. (4) HIV enters helper T-lymphocytes (TH), replicates and produces progeny viruses. (5) Progeny viruses released into blood attack other helper T cells. (6) This is repeated, leading to a progressive decrease in TH cells. There is always a time lag between infection and appearance of AIDS symptoms — from a few months to many years (usually 5-10 years). Symptoms show when the number of helper T cells falls sharply and the person develops bouts of fever, diarrhoea, weight loss and opportunistic infections.
Go deeper
Diagnosis uses ELISA. Treatment with anti-retroviral drugs is only partially effective: they can prolong life but cannot prevent death from AIDS.
From Class 10
HIV hides its genes inside our own cells and uses them as factories to make more viruses, slowly destroying the immune system.