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Understanding Viruses and the Common Cold

Feb 10, 2025

Lecture Notes: Understanding Viruses and the Common Cold

Introduction

  • Common cold causes sneezing, coughing, and general malaise.
  • Cannot be treated with antibiotics; caused by a virus.

What is a Virus?

  • Definition: Viruses are not cells and are not classified as living things.
  • Debate exists whether they are considered nonliving.
  • Comparison:
    • Antibiotics target bacteria (e.g., E. coli), which are living cells.
    • Anti-fungal medications target fungi (e.g., athlete’s foot).

Structure of Viruses

  • Size: Much smaller than cells, require an electron microscope to see.
  • Shapes: Varied forms; bacteriophage is a common example that attacks bacteria.
  • Components:
    • Genetic material (DNA or RNA).
    • Protein coat (capsid) that protects the genetic material.
    • Some viruses have additional structures (enzymes, outer envelope).

Viral Replication

  • Viruses require a host to replicate.

Lytic Cycle

  1. Virus attaches to a host cell.
  2. Injects DNA/RNA into the cell (or is taken in).
  3. Host cell uses its resources to make copies of the virus.
  4. Host cell membrane ruptures (lysis), releasing new viruses to infect other cells.
  5. Result: Host cell death.

Lysogenic Cycle

  • Overview: Longer, sneaky process.
  1. Virus injects genetic material, which integrates into host's genetic material.
  2. Host cell replicates its own and viral genetic material during cell division.
  3. Trigger (chemical, lack of food) can activate the lytic cycle later.

Example: The Common Cold

  • Typically runs its course; immune system usually handles it.

Example: HIV

  • Specificity: Binds to CD4 glycoprotein on Helper T cells, crucial for the immune system.
  • Consequence: Makes individuals vulnerable to infections.
  • Treatments: Medications developed to slow HIV replication; ongoing research for prevention strategies.
  • Challenge: Viral mutations make treatments potentially ineffective.

Positive Aspects of Viruses

  1. Gene Therapy: Viruses can play a useful role.
  2. Pest Control: Some viruses target pest insects, potentially serving as alternatives to chemical pesticides (e.g., Nuclear Polyhedrosis Virus).
  3. Ecological Considerations: Any pesticide (chemical or viral) can have ecosystem consequences.

Conclusion

  • Always stay curious about viruses and their roles!

Full transcript