Lab 2 Practical Virology - Page-by-Page Notes

Page 1

• Lab 2: Practical Virology
• Main topics:
  • 1) Definition of viruses
  • 2) Virions
  • 3) Shapes of viruses
  • 4) Spreading of viruses

Page 2

• Virus definition:

  • A virus is a small infectious agent that replicates only inside the living cells of other organisms. Viruses can infect all types of life from animals and plants to microorganisms including bacteria and archaea. Viruses are found in almost every ecosystem on earth. The study of viruses is called virology, a sub-specialty of microbiology.

• Virion definition:

  • A virion is the complete virus particle, consisting of:
    1) The genetic material made from either DNA or RNA (a long molecule that carries genetic information).
    2) A protein called the capsid which surrounds and protects the genetic material.
    3) An envelope of lipids that surrounds the protein coat when the virion is outside the cell.

• Virus shapes (intro):

  • 1) Simple helical: capsid shaped into a filamentous or rod structure; has a central cavity that encloses its nucleic acid; some of these viruses are short, others are long. Example: Tobacco mosaic virus (TMV) – Simple helix.

  • 2) Icosahedral form (Polyhedral): consists of identical subunits that form an icosahedron (equilateral triangular faces). Because the protein subunits are identical, the virus conserves energy and genetic economy by not encoding many different kinds of capsid proteins. Example: adenovirus.

• Quick note on terminology:

  • Simple helical and Icosahedral are two canonical symmetry types used to describe viral capsids. Other forms exist (see Page 3).

• Key concept: genetic economy

  • Because capsid proteins are encoded by identical subunits, viruses minimize genome size while maintaining protective structure.

• Example reference:

  • Adenovirus as an example of an icosahedral, polyhedral capsid.

• Spreading of viruses (overview, leading into Page 3):

  • Plant viruses are often transmitted from plants by insects that feed on plant sap (e.g., aphids).
  • Animal viruses can be carried by blood-sucking organisms that serve as vectors (e.g., West Nile virus); influenza can spread by coughing and sneezing.
  • Binal form: A combination of spiral and icosahedral symmetry (examples include some T bacteriophages).
  • Complex form: Not purely icosahedral or helical; features extra structures such as a polyhedral “head” and a helical “sheath” with legs/fibers that attach to the cell membrane to transfer the viral genome.

Page 3

• More on virus shapes:

  • 2) Icosahedral form (Polyhedral) [continued]
  • Consists of identical subunits that form equilateral triangles.
  • The use of identical subunits leads to genetic economy and energy conservation, since fewer distinct proteins are needed to build the capsid.
  • Example reaffirmed: adenovirus.

• Spreading of viruses (continued):

  • 1) Plants: transmission by insects (sap-sucking vectors) such as aphids.
  • 2) Animals: vectors are blood-sucking organisms; example West Nile virus. Additionally, respiratory viruses such as influenza spread via coughing and sneezing.
  • 3) Binal form: combination of spiral and icosahedral symmetry (example: some T‑phages).
  • 4) Complex form: head–tail morphology with additional structures (head is polyhedral, tail/sheath is helical, with fibers attaching to the cell membrane to inject the genome).

Page 4

• Example of viral gastroenteritis:

  • Norovirus and rotavirus are common causes of viral gastroenteritis and are transmitted via the fecal–oral route, passing from person to person by contact and entry through contaminated food or water.

• Prevention and treatment:

  • 1) Vaccines: A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe or its toxins.
  • 2) HIV example: HIV is transmitted through sexual contact and exposure to infected blood.

Page 5

• Biosafety requirements (risk groups): Microorganisms can be divided into 4 groups according to risk posed to individuals and the community.

  • Group 1 (no or low individual and community risk): Microorganisms unlikely to cause human or animal disease. Example given: adeno-associated virus (AAV).
  • Group 2 (moderate individual risk, low community risk): Pathogens that can cause human or animal disease but are unlikely to be hazardous to laboratory workers, livestock, or the environment. Examples given: herpes virus, foot-and-mouth disease (FMD) virus. Also mentioned: AAV (though typically described as Group 1 in standard classifications; the text lists it here as well).

• Antivirals (drug treatments):

  • Antibiotics do not work against viral infections such as the common cold or flu.
  • Antiviral drugs work by either inhibiting a virus’s ability to reproduce or by strengthening the body’s immune response to the infection.
  • There are several classes of antiviral drugs, each used for specific kinds of viral infections.

Page 6

• Biosafety risk groups (continued):

  • Group 3 (high individual risk, low community risk): Pathogens that usually cause serious disease in humans or animals but are not readily spread from one infected individual to another. Examples given: HIV, Rabies.
  • Group 4 (high individual and high community risk): Pathogens that usually cause serious human or animal disease and can be readily transmitted from one individual to another, via direct or indirect methods. Examples given: Ebola virus, HIV.

• Observations and practical implications:

  • The source text provides specific examples for each risk group, illustrating how biosafety classification informs handling, containment, and preventive measures.
  • Note that some viruses (e.g., HIV) appear in multiple contexts within the notes; real-world classifications may vary, and organizations typically assign a single risk group per agent based on standardized criteria.

• Connections to foundational principles and real-world relevance:
  • Understanding virion structure (DNA/RNA, capsid, envelope) underpins vaccine design and antiviral targets.
  • Virus shapes and symmetry relate to stability, assembly, and infection mechanisms.
  • Transmission routes (vector-borne, fecal–oral, respiratory) determine public health interventions.
  • Vaccination and antiviral strategies reflect core approaches to controlling viral infections.
  • Biosafety risk groups guide laboratory practices, containment, and ethical responsibility in research and healthcare.

• Key definitions (summary):

  • Virus: A small infectious agent that replicates only inside living cells of other organisms.
  • Virion: The complete, extrinsic virus particle with genome, capsid, and, if present, a lipid envelope.
  • Capsid: Protein shell protecting the viral genome.
  • Envelope: Lipid membrane surrounding the capsid in some viruses when outside host cells.
  • DNA, RNA: The genetic material of viruses.

• Important examples mentioned:

  • Tobacco mosaic virus (TMV) – simple helical.
  • Adenovirus – Icosahedral form.
  • Norovirus and Rotavirus – fecal–oral transmission causing gastroenteritis.
  • West Nile virus – vector-borne transmission:
  • HIV and Rabies – high-prevalence, high-impact pathogens used as examples in risk group sections.
  • Ebola virus – example of high-risk group 4 pathogen.

• Notation and terminology to remember:

  • Phases of viral spread: plant vectors (aphids), animal vectors (blood-sucking insects), respiratory spread (coughing/sneezing), and structural forms (helical, icosahedral, binal, complex).
  • Risk groups for biosafety: 1–4 with examples and containment implications.