Free Science Lessons: Human Immunodeficiency Virus (HIV) and Acquired Immunodeficiency Syndrome (AIDS)

Objectives

• Describe the structure of the Human Immunodeficiency Virus (HIV).
• Explain how HIV replicates.
• Understand how HIV causes the symptoms of AIDS.
• Understand why viruses cannot be treated using antibiotics.

Structure of HIV

• Type: RNA virus
  • Contains two RNA strands.
• Capsid: Protein shell housing the RNA strands.
• Enzymes: Includes reverse transcriptase.
• Lipid Envelope: Surrounds the virus externally.
• Attachment Proteins: Located on the envelope to attach to host cells.
• Matrix Proteins: Located just inside the lipid envelope to maintain virus structure.

Replication of HIV

1. Infection: HIV particles circulate the bloodstream in an infected person (HIV positive).
2. Target Cell: Main target is helper T cells.
   • Attachment protein binds to CD4 molecules on helper T cells.
3. Fusion and Entry: Lipid envelope fuses with cell membrane, allowing capsid entry.
4. Conversion:
   • Reverse transcriptase converts viral RNA to double-stranded DNA.
   • The viral DNA integrates with host DNA in the nucleus.
5. Dormancy: Viral DNA may remain dormant for years.
6. Activation:
   • Viral DNA becomes active, producing RNA.
   • Messenger RNA encodes viral proteins and RNA genome.
7. Protein Production: RNA moves to cytoplasm, where ribosomes translate it into proteins.
8. Assembly and Release:
   • Virus particles assemble and bud from helper T cell.
   • Forms lipid envelope from cell membrane.

• HIV as Retrovirus: Converts RNA to DNA using reverse transcriptase.

HIV and AIDS

• Helper T Cells Death: Leads to decreased immune function.
• Immune System Failure:
  • Reduced antibody production by B lymphocytes.
  • Less effective cell-mediated immune response.
• AIDS:
  • Increased vulnerability to opportunistic infections (e.g., tuberculosis).
  • Higher risk of cancers; these are causes of death in AIDS patients.

Antibiotics vs. Antiviral Drugs

• Antibiotics:
  • Target bacterial structures or metabolism.
  • Example: Penicillin prevents bacterial cell wall synthesis, causing cell lysis.
• Viruses: Lack cellular structure and use host cell metabolism.
  • Cannot be treated with antibiotics.
• Antiviral Drugs:
  • Used to treat viral infections.
  • Example: HIV antiviral drugs inhibit reverse transcriptase and other enzymes.

Conclusion

• Understanding HIV structure and replication is crucial for comprehending how it leads to AIDS and why specific treatments are necessary.