1/29 Introduction to Virus Pg. 1-5

Introduction to Microscopy and Magnification

  • Start of the animation depicting a human hand holding a pin.

  • Explanation of magnification process.

    • Begins at no magnification (20 millimeters).

    • Zooming in 10 times to see details on the head of the pin.

Sizes of Microorganisms

  • Magnification levels:

    • 0X Magnification (20 mm): Standard view with human eye, reveals the pin.

    • 10X Magnification (2 mm): Allows visibility of a human hair and initial dust mites.

    • Dust Mites:

      • Microscopic, multicellular organisms.

      • Feeds on human dead skin; not harmful.

    • 100X Magnification (200 µm):

    • Additional visibility of dust mites and other microorganisms.

    • 1,000X Magnification (20 µm):

    • Identification of ragweed pollen (plant reproductive structure).

      • Description: "Plant sperm"; many may be allergic to it.

    • Recognition of a white blood cell (lymphocyte) and two red blood cells.

    • Identification of a yeast cell (unicellular fungi).

    • 10,000X Magnification (2 µm):

    • Begins to show bacteria (E. coli, Staphylococcus).

      • E. coli description: rod-shaped.

      • Staphylococcus description: circular; "coccus" refers to circular shape.

    • 100,000X Magnification (200 nm):

    • Visibility of viruses, such as Ebola.

    • 1,000,000X Magnification (20 nm):

    • Visibility of rhinovirus (common cold virus).

      • Discusses ease of transmission through aerosols (coughs/sneezes).

Understanding Viruses

  • Characteristics of Viruses:

    • Nucleic Acid: All viruses contain RNA or DNA.

    • Types:

      • DNA viruses (single-stranded and double-stranded).

      • RNA viruses (single-stranded and double-stranded).

    • Capsid: Protection of the nucleic acid made from proteins.

    • Shapes:

      • Icosahedral (20-sided geometric).

      • Helical (rod shape).

    • Envelope:

    • Some viruses possess an envelope (called enveloped viruses); if absent, termed naked viruses.

    • Originates from the host's cellular membrane during viral replication.

    • Contains phospholipid bilayer and spike proteins.

Mechanism of Viral Infection

  • Viral Specificity:

    • Viruses are usually specific to hosts (e.g., human vs. plant viruses).

    • New virus example: Current virus spilling over from bats to pigs to humans.

    • Fatality rate: 40% to 75% (not highly transmissible).

Viral Mutations and Reverse Transcriptase

  • Some viruses can mutate and evolve due to reverse transcriptase, an enzyme that converts RNA back to DNA.

    • High mutation rate facilitates evasion from the immune response.

    • Significance in vaccines (e.g., HIV vaccine development).

Classification of Viruses

  • Categories based on morphology:

    • Enveloped polyhedric: Examples include HIV and influenza.

    • Naked polyhedric: Example includes adenovirus common cold.

    • Spiral: Example includes the tobacco mosaic virus (plant virus).

    • Bacteriophage: Specifically infects bacteria.

Steps in Viral Infection

  1. Adsorption:

    • Virus binds to the host cell membrane via specific receptor interactions.

  2. Penetration:

    • Non-enveloped viruses are engulfed by receptor-mediated endocytosis.

    • Enveloped viruses fuse with the host membrane, entering the cell.

  3. Uncoating:

    • Capsid breakdown exposes the viral nucleic acid.

  4. Synthesis:

    • Virus commandeers host cell machinery, halting host functions.

  5. Assembly:

    • Newly synthesized viral components are assembled into complete virions.

  6. Release:

    • Non-enveloped viruses often cause cell lysis, while enveloped viruses bud from the cell, incorporating part of the host membrane.

Immune Response and Symptoms of Infection

  • Viruses may kill host cells during replication:

    • Resulting symptoms include cough, mucus, inflammation, and a weakened immune response.

  • The body’s response can lead to significant cell injury and sickness.

Specifics of Bacteriophage Activity

  • Bacteriophages target bacterial cells specifically, utilizing:

    • Tail fibers for adherence to bacterial membranes.

  • Injection of DNA into bacteria using enzymes to breach the bacterial cell wall.

  • Viral strategies: Lytic vs. Lysogenic cycles:

    • Lytic cycle: Immediate viral replication and cell destruction.

    • Lysogenic cycle: Viral DNA integrates into the host genome, remaining dormant until conditions are favorable for replication.

Summary of Processes in Viral Life Cycle

  1. Lytic Cycle Processes:

    • Attach, inject, hijack, synthesize, assemble, release.

  2. Lysogenic Cycle Processes:

    • Integrate into host genome; replicate upon favorable environmental conditions.

Conclusion and Next Steps

  • Summary of viral behaviors and characteristics.

  • Open floor for questions regarding processes and mechanisms discussed.