Viral Biology Overview

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Questions and Answers

Which type of viral structure is characterized by a flexible filament and contains a helical tube around the genome?

  • Amorphous virus
  • Filamentous virus (correct)
  • Complex-tailed bacteriophage
  • Icosahedral virus

What is a defining characteristic of complex-tailed bacteriophages?

  • Their genetic material is only RNA.
  • They are amorphous with spike proteins.
  • They have no envelope.
  • They inject genetic material into host cells. (correct)

Which virus is known for its ability to rapidly mutate, leading to new strains that evade immune recognition?

  • Ebola virus
  • Smallpox virus
  • Herpes simplex virus
  • Influenza virus (correct)

Which statement about viral genome size is accurate?

<p>Retroviruses classify under small RNA genomes. (C)</p> Signup and view all the answers

What is the role of spike proteins in enveloped viruses?

<p>To interact with host cell receptors. (A)</p> Signup and view all the answers

What type of viruses lack a symmetrical form and typically have a flexible core structure?

<p>Amorphous viruses (C)</p> Signup and view all the answers

What distinguishes the Baltimore Classification system of viruses?

<p>It groups viruses based on their method of replication. (B)</p> Signup and view all the answers

Which of the following structures is NOT part of the virus structure summary?

<p>Genetic scaffolding (B)</p> Signup and view all the answers

Which category of viruses specifically targets bacterial cells?

<p>Bacteriophages (C)</p> Signup and view all the answers

What component may be present in some viruses and is involved in reverse transcription?

<p>Reverse transcriptase (A)</p> Signup and view all the answers

What is the primary factor that largely determines a virus's host range and tissue tropism?

<p>Surface receptor molecules on the host (C)</p> Signup and view all the answers

Which characteristic does NOT describe the Baltimore classification model of viruses?

<p>Classification based on capsid form (B)</p> Signup and view all the answers

What is one reason why antiviral agents are hard to discover?

<p>Viral genomes mutate more rapidly than bacterial genomes (D)</p> Signup and view all the answers

Which of the following best describes the role of the capsid in a virus?

<p>It keeps the viral genome intact outside the host (C)</p> Signup and view all the answers

What type of symmetry is exhibited by viruses with an icosahedral capsid?

<p>Radial symmetry (A)</p> Signup and view all the answers

What is a significant distinction between DNA and RNA viral genomes?

<p>RNA viruses require synthesis of a complement to encode proteins (A)</p> Signup and view all the answers

Which subtype of viruses is classified based on the presence or absence of an envelope?

<p>Baltimore classification (D)</p> Signup and view all the answers

Which type of virus structure is characterized by having 20 identical triangular faces?

<p>Icosahedral (B)</p> Signup and view all the answers

What can be said about the evolution rate of viruses compared to bacteria?

<p>Viruses evolve faster than bacteria (B)</p> Signup and view all the answers

What is NOT a function of the viral envelope structure?

<p>Energy provision for viral metabolism (B)</p> Signup and view all the answers

What distinguishes viruses from living cells?

<p>Viruses are considered obligate intracellular parasites. (D)</p> Signup and view all the answers

Which class of viral genomes is known for being made up entirely of RNA?

<p>Retroviruses (C)</p> Signup and view all the answers

What is the term used to describe the range of hosts a virus can infect?

<p>Host range (A)</p> Signup and view all the answers

Which of the following accurately describes the Virus-First Model of virus origin?

<p>Viruses co-evolved alongside cellular life. (A)</p> Signup and view all the answers

Which characteristic is NOT typically associated with viruses?

<p>Ability to replicate in vitro (A)</p> Signup and view all the answers

What is tissue tropism in relation to viruses?

<p>The preference of a virus for specific types of cells. (B)</p> Signup and view all the answers

In the Reduction Model of virus origin, viruses are thought to have:

<p>Regressed from free-living organisms. (D)</p> Signup and view all the answers

Which component is a major structural element of all virions?

<p>Capsid (D)</p> Signup and view all the answers

Viruses are known to infect which of the following groups of organisms?

<p>Bacteria, eukaryotes, and archaea (B)</p> Signup and view all the answers

What is the primary distinction between the Escape Model and the Reduction Model regarding virus origin?

<p>The Escape Model involves genetic elements escaping from cells. (C)</p> Signup and view all the answers

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Study Notes

Viruses and Their Nature

  • Viruses are ubiquitous, infecting all forms of life, including bacteria, archaea, and eukaryotes.
  • They cause significant diseases in humans, such as influenza and the common cold.
  • Viruses are obligate intracellular parasites, meaning they can only replicate within a host cell.
  • They are distinct from cells as they lack ribosomes and other components necessary for independent life.
  • Viral infection leads to viral replication, which can result in host cell death or debilitating effects.

Viral Genomic Diversity

  • Viral genomes are composed of either DNA or RNA, which can be single- or double-stranded.
  • The Baltimore classification system groups viruses based on their genome type, strand, and replication strategy.
  • The capsid protects the viral genome outside of the host cell.
  • Some viruses also have an envelope derived from the host membrane, studded with viral envelope proteins.

Viral Structure and Diversity

  • Viral structure varies, with three main categories: icosahedral, filamentous, and complex.
  • Icosahedral capsids have radial symmetry, forming a polyhedron with 20 identical triangular faces (e.g., herpes simplex virus).
  • Filamentous viruses have helical symmetry, generating a flexible filament (e.g., Ebola virus).
  • Complex viruses have a complex structure not easily categorized, often with a flexible "core wall" containing genetic material and a viral envelope with spike proteins (e.g., smallpox virus).

Viral Genome Size and Evolution

  • RNA viruses generally have smaller genomes compared to DNA viruses.
  • Some viruses, like retroviruses, have RNA genomes, while others like herpes simplex virus have large DNA genomes.
  • Viruses evolve quickly due to antigenic drift, where rapid mutations lead to new strains that are not recognized by existing antibodies.
  • This constant evolution necessitates repeated immunizations for viruses like influenza.

The International Committee on Taxonomy of Viruses (ICTV)

  • Classifies viruses based on multiple factors, including:
    • Capsid form (icosahedral or filamentous).
    • Envelope (present or absent).
    • Host range.

Host Range and Tissue Tropism

  • Host range refers to the species a virus can infect.
  • Tissue tropism describes the specific tissues a virus can infect within a host.
  • Both factors are determined by the availability of suitable receptor molecules on the host cell surface.

Challenges in Antiviral Drug Discovery

  • Antiviral drug discovery is complex and challenging due to:
    • The requirement for specific virus-encoded proteins to commandeer host metabolism.
    • The difficulty in targeting viral proteins without causing harm to the host.
    • The rapid mutation rate of viral genomes, making drug resistance a constant threat.

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