Chapter 6 Viruses Overview
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Questions and Answers

What defines the host range of a virus?

  • The size and shape of the virus particles
  • The variety of organisms a virus can infect (correct)
  • The specific type of cells a virus can attach to
  • The temperature range in which a virus is active

    • What characterizes a bacteriophage?

  • It is composed solely of DNA
  • It can infect human cells directly
  • It infects and replicates within a bacterial cell (correct)
  • It can infect both plant and animal cells

    • What is the primary function of +ssRNA during viral replication?

  • It assists in the assembly of new virus particles
  • It serves as a template for new viral proteins
  • It provides the genetic code for protein synthesis (correct)
  • It aids in the lysis of host cells

    • What is the main difference between virulent and temperate phages?

    <p>Virulent phages undergo the lytic cycle, while temperate phages can enter a lysogenic cycle</p> Signup and view all the answers

    What process describes the entry of the entire virus into a host cell?

    <p>Penetration</p> Signup and view all the answers

    Which statement accurately describes the maturation phase in bacteriophage replication?

    <p>New phage particles are assembled</p> Signup and view all the answers

    How do enveloped viruses penetrate host cells?

    <p>By fusing with the plasma membrane</p> Signup and view all the answers

    What initiates the switch of a temperate phage from the lysogenic cycle to the lytic cycle?

    <p>Environmental stressors affecting the host</p> Signup and view all the answers

    What distinguishes the capsid forms of viruses?

    <p>Their structural organization, such as helical or icosahedral</p> Signup and view all the answers

    What role does -ssRNA play in the replication process of viruses?

    <p>It serves as a template for synthesizing +ssRNA</p> Signup and view all the answers

    What role does reverse transcriptase play in retroviruses?

    <p>It produces DNA from RNA.</p> Signup and view all the answers

    What is one method used to cultivate animal viruses?

    <p>Fertilized chicken eggs.</p> Signup and view all the answers

    What is a plaque in the context of bacteriophage cultivation?

    <p>A clear zone in a bacterial lawn.</p> Signup and view all the answers

    What distinguishes virusoids from viroids?

    <p>Virusoids require a helper virus to replicate.</p> Signup and view all the answers

    What is the purpose of antiviral drugs that block penetration or uncoating?

    <p>To inhibit the virus from entering the host cell.</p> Signup and view all the answers

    What characterizes prion proteins associated with disease?

    <p>They are misfolded proteins causing normal proteins to misfold.</p> Signup and view all the answers

    What is the term for the maximum number of virions produced per bacterium in a viral growth curve?

    <p>Burst size.</p> Signup and view all the answers

    Which characteristics define primary cell cultures?

    <p>Isolated from animal tissues and have a limited lifespan.</p> Signup and view all the answers

    What is NOT a method that scientists use to detect viruses?

    <p>Blood tests for antibodies.</p> Signup and view all the answers

    What outcome is expected from the interaction between PrPC and PrPSc?

    <p>PrPC converts to PrPSc and accumulates.</p> Signup and view all the answers

    Study Notes

    Acellular Pathogens: Viruses

    • Definition: Viruses are submicroscopic, infectious, parasitic, non-living agents. They consist of nucleic acid (DNA or RNA, single or double-stranded, circular or linear) surrounded by a protein coat (capsid).

    Capsid Structures

    • Forms: Capsids have three basic shapes: helical, icosahedral, and complex (a combination of the first two).

    Host Range and Specificity

    • Host range: The range of organisms a virus can infect.
    • Tissue specificity: Within a host organism, viruses infect specific tissues or organs.
    • Bacteriophages: Infect specific bacterial species.
    • Smallpox: Infects only humans.
    • Classification criteria: Host organism, morphology (capsid structure), and genome type (DNA or RNA).

    Viral RNA Types

    • +ssRNA: Contains the code for protein synthesis and can be directly translated by ribosomes.
    • -ssRNA: Requires an intermediate step; it serves as a template to create +ssRNA, which is then used for protein synthesis.

    Bacteriophages

    • Definition: A bacteriophage is a virus that infects and replicates within a bacterial cell.
    • Replication steps:
      • Attachment: Phage attaches to the bacterial host cell.
      • Penetration: Viral DNA enters the host cell (but the capsid does not enter the cytoplasm).
      • Biosynthesis: Phage DNA is replicated and phage proteins are produced, hijacking the host cell's machinery.
      • Maturation: New phage particles are assembled.
      • Lysis: The host cell is broken open, releasing newly formed phages.

    Phage Types

    • Virulent phages: Undergo the lytic cycle, resulting in the death of the host cell.

    • Temperate phages: Undergo the lysogenic cycle, integrating their DNA into the host cell's genome, replicating with the host until stress triggers the lytic cycle.

    • Lytic cycle trigger: Stress induces temperate phages to switch to the lytic cycle.

    Animal Virus Replication

    • Differences from bacteriophages: Replicates differently inside animal host cells compared to bacteria.
    • Uncoating: The process where the viral nucleic acid is released from the capsid.

    Viral Penetration

    • Enveloped viruses: Fusing with the host cell's plasma membrane, releasing the nucleocapsid into the cytoplasm.
    • Non-enveloped viruses: Entering the cell by endocytosis (engulfment).

    Viral RNA Replication

    +ssRNA - Codes for protein synthesis directly on its own.

    • ssRNA - Creates a +ssRNA template to provide the code for protein synthesis.

    Viral Release

    • Enveloped viruses: Release by pushing through the host cell membrane, acquiring an envelope in the process, or budding (fusing with the plasma membrane and releasing the virus).

    Retroviruses

    • Definition: An RNA virus.
    • Key enzyme: Reverse transcriptase - converts their RNA into DNA.

    Viral Growth Curve

    • Steps: Includes Inoculation, Eclipse, Burst phases and defining Burst size - maximum virions per bacterium.

    Animal Virus Cultivation

    • Techniques:
      • Fertilized chicken eggs: Used for growing animal viruses (amniotic cavity, chorioallantoic membrane, yolk sac).
      • Cell cultures:
        • Primary cell cultures: Isolated from animal tissues, limited lifespan due to contact inhibition.
        • Secondary cell cultures: Derived from primary cultures, increased lifespan.
        • Continuous cell lines: Derived from transformed cells/tumors, unlimited growth potential, unresponsive to contact inhibition.

    Bacteriophage Cultivation

    • Method: Cultivation on a 'bacterial lawn'.

    Plaque Formation

    • Definition: Clear zones on a bacterial lawn indicating areas where bacteriophages have lysed bacterial cells.

    Virus Detection

    • Methods: Observing cytopathic effects (structural changes) under a microscope (e.g. syncytia, cell inclusions).

    Viroids

    • Definition: Non-infectious, single-stranded RNA molecules causing disease in plants.
    • Characteristics: Need a host cell to replicate, do not encode proteins.
    • Examples: Potato spindle tuber viroid (PSTV), tomato planta macho viroid (TPMVD), Avocado sunblotch viroid (ASBVD)

    Virusoids

    • Definition: Infectious, single-stranded RNA molecules, needing a helper virus to replicate.
    • Characteristics: Do not encode proteins
    • Examples: Subterranean clover mottle virus, Hepatitis B virus

    Prions

    • Definition: Infectious, self-replicating proteins causing diseases.

    • Mechanism: Caused by genetic mutation or spontaneous conversion.

    • Types of prion proteins:

    • PrPc: Normal cellular prion protein.

    • PrPsc: Abnormal, misfolded prion protein; causes prion diseases.

    • Transmission: PrPSC converts normal PrPc to abnormal PrPsc through the formation of heterodimers. The abnormal proteins accumulate causing disease.

    Antiviral Drugs

    • Targets: Various stages of viral replication, including penetration/uncoating, genome replication, and virion maturation/release.
    • Examples of antiviral drugs : (listed by function, not by drug name)
    • Blocking Penetration/Uncoating: Amantadine, Rimantadine, Pleconaril, Envufirtide, Maraviroc
    • Inhibition of Genome Replication: Acyclovir, Ganciclovir, Ribavirin, AZT, Vidarabine , Idoxuridine, Trifluridine, Dideoxycytidine, Dideoxyinosine, Foscarnet, Nevirapine, Delavirdine, Raltegravir
    • Inhibition of Virion Maturation/Release: Indinavir, Ritonavir, Saquinavir, Oseltamivir, Zanamivir

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    Description

    Explore the fascinating world of viruses, including their structures, host range, and classification. This quiz covers the essential aspects of viral morphology, RNA types, and their specificity. Test your knowledge of these acellular pathogens and their roles in infections.

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