Virus Lecture Notes Flashcards

Virus Introduction and Structure

• What is a virus?
  A virus is a microscopic infectious agent that requires a living host cell to replicate and propagate its genetic material. It is composed of genetic material encased in a protein coat and, in some cases, a lipid envelope.

• Viruses are nonliving:

  • Viruses do not exhibit characteristics of living organisms, such as metabolism or cellular organization.
  • They cannot reproduce independently; they must infect a host cell and hijack its machinery for replication.

• Examples of viral diseases:

  • Influenza, HIV/AIDS, Hepatitis B and C, measles, and COVID-19.

• Suspected origin of viruses:
  Viruses may have originated from genetic material that escaped from cells and began to replicate independently. It is theorized that they evolved alongside cells or even from them.

• Ranking sizes:

  1. Virus
  2. Prokaryotic cell
  3. Eukaryotic cell

• Outer layer of a virus:

  • The outer layer is called the capsid, made of protein subunits (capsomers). Inside, there is nucleic acid, which can be either DNA or RNA, but never both.

Viral Infection

• Define bacteriophage:
  A bacteriophage is a type of virus that infects bacteria. They attach to bacterial cells and inject their genetic material, leading to the bacteria's destruction or malfunction.

• Reproductive requirement for a virus:
  A virus requires a host cell to reproduce, utilizing the cell’s metabolic machinery for its replication.

• Lytic cycle:

  1. The virus attaches to the host cell and injects its DNA.
  2. The host's cellular machinery is reprogrammed to replicate the viral components.
  3. New viruses are assembled and eventually cause the host cell to burst (lyse), releasing the new viruses.
  • Lyse:
    The process in which a cell breaks down and releases new virions.
  • Active virus examples:
    Influenza, adenoviruses.

• Lysogenic cycle:

  1. The virus integrates its DNA into the host cell’s genome and remains dormant.
  2. The viral DNA can be replicated along with the host’s DNA during cell division without causing symptoms.
  • Latent virus examples:
    Herpes simplex virus, HIV.

• Lytic vs. Lysogenic cycle:

  • The lytic infection cycle is relatively short, with symptoms appearing in 1-4 days.
  • The lysogenic infection cycle is longer, as the virus can remain dormant for extended periods.

Connection Between Lytic and Lysogenic Cycles

• Both cycles are methods of viral reproduction, but differ in their effects on the host cell and timing of symptoms.
• The lysogenic cycle can transition to the lytic cycle under certain conditions, leading to active symptoms.

Retroviruses

• Define retrovirus: A retrovirus is a type of virus that uses reverse transcription to convert its RNA into DNA after entering a host cell. This DNA integrates into the host's genome.
  • Common examples:
    Human Immunodeficiency Virus (HIV), Human T-Lymphotropic Virus (HTLV).

Miscellaneous Info

• Define pathogen:
  A pathogen is any organism that can cause disease, including viruses, bacteria, fungi, and parasites.

• What is a vaccine?
  A vaccine is a biological preparation that provides active acquired immunity to a particular infectious disease. It contains antigens that stimulate the immune system.

• Immunity through vaccinations:
  Vaccinations introduce harmless components or weakened forms of a pathogen, stimulating the immune response to build antibodies and memory cells without causing disease.

• Diseases with vaccines:
  Measles, mumps, rubella, polio, hepatitis, influenza, and COVID-19.