Virus Structures and Life Cycles

Virus Structures and Life Cycles

• Definition of Viruses:

  • Viruses are nonliving particles requiring a host for reproduction. They do not fulfill all life characteristics.
  • Lack organelles for nutrient absorption and energy use.
  • Cannot replicate independently or synthesize proteins.
  • Some viruses infect and harm various living organisms.

• Virus Structure Components:

  • Capsid: The protective protein coat surrounding the virus.
  • Genetic Material: Can be DNA or RNA; serves as the instruction manual for the virus.

• Classification from Smallest to Largest:

  • General order from smallest to largest: Prion < Viroid < Virus < Prokaryotic Cell < Eukaryotic Cell.

• Virus Replication Process:

  • A virus must enter a host cell to replicate.
  • Attachment to the host cell results in the entry of genetic material into the cytoplasm.
  • Sometimes, the entire virus enters the cell, leading to the breakdown of the capsid.

• Viral Life Cycles:

  • Lytic Cycle:
  • Virus binds to host cell and injects genetic material.
  • Host cellular machinery is used to produce viral components.
  • New viruses assemble and cause the cell to lyse (burst), releasing new viruses.
  • Lead time for symptoms: Rapid onset.
  • Lysogenic Cycle:
  • Viral DNA integrates into host DNA (becomes a prophage).
  • Viral DNA is replicated along with host DNA during cell division.
  • Can switch to the lytic cycle under certain triggers.
  • Lead time for symptoms: Symptoms may take time to appear (latent).

• Bacteriophage:

  • A type of virus that specifically infects bacteria.
  • Mechanism of attack involves injecting genetic material into the host bacterium.

• Retrovirus Overview:

  • Retrovirus is defined by the presence of RNA and the enzyme reverse transcriptase which enables the conversion of RNA to DNA.
  • Human Immunodeficiency Virus (HIV):
  • Causes Acquired Immunodeficiency Syndrome (AIDS).
  • Targets CD4+ T cells, which play a vital role in the immune response.

• Key Components of HIV:

  • Capsid: Protects viral RNA.
  • RNA: Carries the virus's genetic information.
  • Glycoproteins: Help virus attach and enter host cells.
  • Viral Envelope: Surrounds capsid and aids in entry into the host cell.
  • Reverse Transcriptase: Converts viral RNA into DNA for integration into the host genome.

• Understanding Vaccines:

  • The virus in a vaccine is weaker than the actual pathogen.
  • Upon exposure to a pathogen, the body produces antibodies to fight it and remember it for future encounters.
  • Antibodies recognize surface antigens on the virus.
  • True/False: Antibodies and antigens have specific shapes that match each other (True).
  • No vaccine exists for the bacteria causing strep throat because treatment requires antibiotics, not vaccination.