W2-7 Viral replication and antiviral targets
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Questions and Answers

During the eclipse phase of the viral replication process, what is happening inside the host cell?

  • The virus has been neutralized by the host immune response
  • The virus has been lysed by the host cell
  • The virus is actively replicating and producing new viral particles
  • The virus has entered the host cell but is not yet producing new viral particles (correct)

    • What is the difference between susceptibility and permissiveness in the context of viral replication?

  • Susceptibility refers to the ability of a virus to infect a cell, while permissiveness refers to the ability of a cell to support viral replication (correct)
  • Susceptibility refers to the ability of a virus to cause disease, while permissiveness refers to the ability of a cell to resist infection
  • Susceptibility refers to the ability of a cell to support viral replication, while permissiveness refers to the ability of a virus to infect a cell
  • Susceptibility refers to the ability of a cell to be infected, while permissiveness refers to the ability of a virus to cause disease

    • Why do some viruses encode their own polymerases and cell-cycle regulators?

  • To enhance the pathogenicity of the virus
  • To evade detection by the host immune system
  • To prevent the host cell from undergoing apoptosis
  • To ensure accurate and efficient replication within the host cell (correct)

    • What characterizes immediate early proteins in viral replicative cycles?

    <p>They are expressed before early proteins and are involved in regulating host cell machinery</p> Signup and view all the answers

    Which factor influences tissue tropism, pathogenesis, and host specificity in viral replication?

    <p>The type of entry receptor on the host cell membrane</p> Signup and view all the answers

    What is a common goal of antiviral therapy?

    <p>To inhibit viral replication or reduce viral load within the host</p> Signup and view all the answers

    What is the minimum requirement for a virus to replicate?

    <p>Nucleic acid genome and a protein coating</p> Signup and view all the answers

    Which of the following accurately describes viruses?

    <p>Infectious, obligately intracellular parasites</p> Signup and view all the answers

    What differentiates viruses from other microbes?

    <p>Cannot metabolize and make energy</p> Signup and view all the answers

    What is the role of a virion?

    <p>Deliver the viral genome and lead to a productive infection</p> Signup and view all the answers

    What is a bacteriophage?

    <p>A type of virus that infects bacteria</p> Signup and view all the answers

    What does the term 'nucleoprotein' refer to?

    <p>A specific type of protein that complexes to nucleic acid</p> Signup and view all the answers

    What structure is formed by nucleoproteins complexed directly to nucleic acid?

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

    How is symmetry classified in terms of viral capsid shapes?

    <p>Helical, icosahedral, or complex</p> Signup and view all the answers

    What does an icosahedron consist of?

    <p>20 triangles arranged into pentagons and 12 vertices</p> Signup and view all the answers

    What does the term 'envelope' refer to in relation to viruses?

    <p>A lipid bilayer derived from the host cell that encompasses some viral capsids</p> Signup and view all the answers

    What is the role of a capsid in a virus?

    <p>A protein layer that encompasses and protects the genome</p> Signup and view all the answers

    What is the term for a virus that infects bacteria?

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

    What is the main function of the capsid in a virus?

    <p>To protect the nucleic acid genome and essential proteins</p> Signup and view all the answers

    Which type of virus has a lipid bilayer envelope?

    <p>Enveloped virus</p> Signup and view all the answers

    What is the role of the matrix in some viruses?

    <p>To connect the capsid and envelope</p> Signup and view all the answers

    Which structure is responsible for adhesion in naked viruses?

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

    What are lipid rafts on the host cell membrane targeted for during virus budding?

    <p>Formation of viral attachment proteins</p> Signup and view all the answers

    What can cause denaturation of a protein capsid in a virus?

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

    Which type of virus is more resistant to environmental stresses such as heat and chemicals?

    <p>Naked capsid viruses</p> Signup and view all the answers

    What is the main role of the envelope in an enveloped virus?

    <p>To fuse with the host cell membrane</p> Signup and view all the answers

    Which type of virus has a nucleocapsid or capsid wrapped in a lipid bilayer envelope?

    <p>Enveloped virus</p> Signup and view all the answers

    Which component of a virus is involved in binding to a cell receptor?

    <p>Viral attachment protein</p> Signup and view all the answers

    What is another name for a viral attachment protein?

    <p>Spike glycoprotein</p> Signup and view all the answers

    What is the variety among viruses almost endless due to?

    <p>Viral proteins and enzymes</p> Signup and view all the answers

    Which type of viruses are more likely to survive on inanimate objects?

    <p>Naked viruses</p> Signup and view all the answers

    What is the primary reason that enveloped viruses will not generally reach the intestine?

    <p>Acid sensitivity</p> Signup and view all the answers

    Which type of viruses are almost always responsible for causing diarrhea?

    <p>Naked viruses</p> Signup and view all the answers

    What is more likely to inactivate enveloped viruses than naked viruses?

    <p>Detergents and mild disinfectants</p> Signup and view all the answers

    What is one benefit of the envelope that a virus can carry?

    <p>Ability to carry more proteins on its surface (answer)</p> Signup and view all the answers

    How are viruses grouped for easier study?

    <p>Based on shared genetics and characteristics (answer)</p> Signup and view all the answers

    What suffix do viral families end in?

    <p>-viridae (answer)</p> Signup and view all the answers

    Which type of viral genomes can be segmented?

    <p>(−) RNA genomes (answer)</p> Signup and view all the answers

    Which type of capsid symmetry is associated with a tubular or helicoidal structure?

    <p>Helical symmetry (answer)</p> Signup and view all the answers

    What is the term for the time between viral entry and new progeny release?

    <p>Latent period</p> Signup and view all the answers

    What is the term for a way to visualize the presence of an infectious lytic viral particle and count them?

    <p>Plaque-forming unit (pfu)</p> Signup and view all the answers

    Which step in the viral replicative cycle involves the binding of the virion to the host cell?

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

    How do most naked viruses enter cells?

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

    What is the mechanism through which some naked viruses enter cells by transferring the complete virion through the membrane without major lysis?

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

    How do enveloped viruses enter cells by fusion of the viral envelope and the plasma membrane of the cell?

    <p>Direct fusion</p> Signup and view all the answers

    What is the term for cell surface molecules that viral attachment proteins (VAPs) may bind to during viral adhesion?

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

    What kind of forces are likely responsible for the initial contact between viral attachment proteins and cell receptors?

    <p>Electrostatic forces</p> Signup and view all the answers

    What kind of forces often lead to conformational changes that initiate the molecular cascade causing virion entry?

    <p>Hydrophobic forces</p> Signup and view all the answers

    What compensates for weak molecular specificity in the case of virion binding to a single receptor molecule?

    <p>Molecular avidity</p> Signup and view all the answers

    What is used to block virion binding and neutralize the virus, making it a common vaccine target?

    <p>VAP-specific antibodies</p> Signup and view all the answers

    For enveloped viruses, what part of the virus is the viral attachment protein (VAP)?

    <p>Membrane protein</p> Signup and view all the answers

    During which step of the viral replicative cycle does the production of nucleic acids and proteins take place?

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

    Which term refers to the ability of a host cell to recognize, follow, and complete the instructions coded within the viral genome?

    <p>Cell permissiveness</p> Signup and view all the answers

    What determines organ, tissue, and cell tropism of a virus and helps define aspects of its epidemiology and pathophysiology?

    <p>Host cell permissiveness</p> Signup and view all the answers

    What is the period between when an infecting virus has fallen apart and when the first progeny are assembled inside the cell called?

    <p>Eclipse period</p> Signup and view all the answers

    Which term refers to the range of cells that a virus is able to attach to based on possessing the needed receptor on its surface?

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

    What characterizes a susceptible cell in relation to viral attachment?

    <p>Has needed receptor on its surface</p> Signup and view all the answers

    Which step of the virus replication cycle generally involves the binding of a virion to its cognate receptor(s) on the surface of a susceptible cell?

    <p>Entry (penetration)</p> Signup and view all the answers

    What determines host specificity and helps define organ, tissue, and cell tropism in viral infectious diseases?

    <p>Host cell susceptibility</p> Signup and view all the answers

    What term is used to describe the period between when an infecting virus has fallen apart and when the first progeny are assembled inside the cell?

    <p>Eclipse period</p> Signup and view all the answers

    What factor determines whether a virus will be able to replicate inside a host cell?

    <p>Cell permissiveness</p> Signup and view all the answers

    What characterizes a permissive host cell that allows for infective viral particles to be produced?

    <p>Allows replication</p> Signup and view all the answers

    What term refers to the range of cells that a virus is able to attach to based on possessing the needed receptor on its surface?

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

    How do viruses achieve movement toward deeper compartments of the cell, such as the nucleus?

    <p>Microtubule-dependent transport</p> Signup and view all the answers

    What is the primary mechanism of peripheral movement of viruses within a cell?

    <p>Actin filament transport</p> Signup and view all the answers

    When does uncoating of viruses typically begin?

    <p>During viral entry</p> Signup and view all the answers

    Where does replication in the cytoplasm usually occur for some viruses?

    <p>In the cytosol</p> Signup and view all the answers

    Which type of movement is mediated by actin filament transport?

    <p>Short-distance movement</p> Signup and view all the answers

    What is the primary mechanism for movement toward deeper compartments of the cell, such as the nucleus?

    <p>Dynein/dynactin/kinesin-dependent transport</p> Signup and view all the answers

    Which event can trigger uncoating of enveloped viruses?

    <p>Endosome acidification</p> Signup and view all the answers

    How do most DNA viruses gain access to the nucleus for replication?

    <p>Via the nuclear pore complex</p> Signup and view all the answers

    What process allows infection of non-dividing, terminally differentiated cells by viruses?

    <p>Lingering in the cytosol or nucleus</p> Signup and view all the answers

    What is the role of immediate-early proteins in viral replicative cycles?

    <p>Gene transcription regulation</p> Signup and view all the answers

    What is the primary role of viral mRNA in DNA virus replication?

    <p>Serving as a template for protein synthesis</p> Signup and view all the answers

    Which enzyme is typically used by most DNA viruses to replicate their DNA?

    <p>Viral DNA-dependent DNA polymerase</p> Signup and view all the answers

    What is the main strategy for protein production in DNA viruses?

    <p>Splicing viral mRNA</p> Signup and view all the answers

    How do viruses that require the host’s DNA polymerase solve the problem of enzyme accessibility?

    <p>Inducing cell cycling for enzyme activation</p> Signup and view all the answers

    What is amplified by cellular DNA-dependent DNA polymerase in the nucleus?

    <p>Viral dsDNA</p> Signup and view all the answers

    What happens to some of the dsDNA in DNA viruses after transcription into mRNA by cellular RNA polymerase?

    <p>Packaged into newly formed capsids</p> Signup and view all the answers

    What is the main location for protein synthesis using viral mRNA in DNA viruses?

    <p>Endoplasmic reticulum (ER)</p> Signup and view all the answers

    What type of replication scheme can retroviruses fall into based on their nucleic acid replication?

    <p>RNA viruses</p> Signup and view all the answers

    What is the process of enveloped viruses acquiring an external membrane layer?

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

    What is the term for the process of incorporating genomic nucleic acid into the protective capsid of the virus?

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

    How do naked viruses typically exit cells?

    <p>Cell lysis</p> Signup and view all the answers

    Which type of assembly starts with individual structural proteins assembling into more complex protomers?

    <p>Sequential assembly</p> Signup and view all the answers

    What is the term for the process of viruses exiting cells by budding?

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

    How do enveloped viruses generally exit cells?

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

    What is the term for the process whereby some enveloped viruses enter cells by transferring the complete virion through the membrane without major lysis?

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

    What is the primary method of virus release for enveloped viruses?

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

    What is the term for the mechanism through which some enveloped viruses enter cells by fusing their envelope with the plasma membrane?

    <p>Membrane fusion</p> Signup and view all the answers

    What is the process through which some enveloped viruses cause cells to fuse together?

    <p>Membrane fusion</p> Signup and view all the answers

    What is the term for cell destruction and death caused by releasing naked viruses?

    <p>Cell lysis</p> Signup and view all the answers

    What is the term for the period during which an infecting virus has fallen apart and new progeny are assembled inside the cell?

    <p>Nucleoprotein formation</p> Signup and view all the answers

    During which phase of the viral replication cycle does the production of nucleic acids and proteins take place?

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

    What event frequently triggers uncoating of the viral genome?

    <p>Endosome maturation</p> Signup and view all the answers

    Which virus would most likely cause lysis of the host cell?

    <p>Hepatitis A virus</p> Signup and view all the answers

    Which stage of the viral replication cycle is most likely affected by an antiviral drug that inhibits the herpesvirus fusion protein?

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

    What is one unique trait of all viruses?

    <p>Inability to live independently without a host</p> Signup and view all the answers

    What does an enveloped virus finish after exiting the cell?

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

    Which virus uses sialic acid as a receptor for attachment?

    <p>(+)ssRNA virus</p> Signup and view all the answers

    What is required by many viruses to pass from a non-infectious form to infectious virions?

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

    What represents the end of the eclipse phase in the viral replication cycle?

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

    Which event involves modification of both virus and host cell in the case of many enveloped viruses such as influenza virus?

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

    Which polymerase is responsible for retrovirus DNA production?

    <p>Viral RNA-dependent DNA polymerase (answer)</p> Signup and view all the answers

    What is the main reason that RNA viruses are more likely to mutate more quickly than DNA viruses?

    <p>RNA-dependent RNA polymerase lacks proofreading capability</p> Signup and view all the answers

    Why do positive-polarity ssRNA viruses not need to carry their own polymerase upon penetration of the host cell?

    <p>Their RNA-dependent RNA polymerase is translated directly from the viral RNA</p> Signup and view all the answers

    What is the immediate product of reverse transcription in retroviruses?

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

    Why do negative-polarity ssRNA viruses absolutely must carry their RNA-dependent RNA polymerase enzyme when they penetrate the host cell?

    <p>(-) ssRNA is unusable by ribosomes and cells lack RNA-dependent RNA polymerase</p> Signup and view all the answers

    What is the role of an integrase in retroviral replication?

    <p>Integrates the viral DNA into the host's genome</p> Signup and view all the answers

    Why do double-stranded RNA viruses follow the (-) ssRNA replication strategy?

    <p>(+) strand of dsRNA is unusable by ribosomes and requires denaturation by a polymerase</p> Signup and view all the answers

    What is the immediate result of reverse transcription in retroviruses?

    <p>Integration of viral DNA into host genome</p> Signup and view all the answers

    What allows positive-polarity ssRNA viruses to immediately initiate protein synthesis upon penetration of the host cell?

    <p>(+) ssRNA is recognized by ribosomes and can be directly translated</p> Signup and view all the answers

    Why do cells not possess enzymes like RNA-dependent RNA polymerase for viral replication?

    <p>Cells lack the ability to synthesize such enzymes</p> Signup and view all the answers

    What allows retroviruses to integrate their DNA into the host's genome?

    <p>'Integrase' enzyme carried by retroviruses</p> Signup and view all the answers

    Which enzyme is responsible for synthesizing the complementary strand of incoming viral ssDNA in single-stranded DNA (ssDNA) viruses?

    <p>DNA-dependent DNA polymerase</p> Signup and view all the answers

    Which virus is responsible for erythema infectiosum, also called fifth disease or slapped-cheek disease?

    <p>Parvovirus B19</p> Signup and view all the answers

    What is the odd replication strategy employed by gapped (partial) dsDNA viruses like the Hepatitis B virus (Hepadnaviridae)?

    <p>The need for repair of the partially dsDNA to create an entire dsDNA</p> Signup and view all the answers

    What is the function of virus-specific reverse transcriptase synthesized in gapped (partial) dsDNA viruses like the Hepatitis B virus?

    <p>Polymerization of gapped dsDNA from pre-genomic mRNA</p> Signup and view all the answers

    What is the role of RNA-dependent RNA polymerase in RNA viruses?

    <p>Synthesis of complementary RNA strand from viral RNA template</p> Signup and view all the answers

    What happens when negative-polarity (-) ssRNA viruses penetrate the host cell?

    <p>(+) ssRNA gets amplified via a (-) ssRNA intermediate.</p> Signup and view all the answers

    How do positive-polarity (+) ssRNA viruses initiate protein synthesis upon penetration?

    <p>(+) ssRNA connects to ribosomes after penetration.</p> Signup and view all the answers

    What does the viral RNA polymerase of negative-sense RNA viruses result in?

    <p>Synthesis of nested set of mRNAs</p> Signup and view all the answers

    What characterizes protein production strategies in RNA viruses with a segmented genome?

    <p>(+) sense RNA encodes one protein per segment</p> Signup and view all the answers

    What initiates translation of positive-polarity (+) ssRNA viruses' genome into a polyprotein that is cleaved to mature proteins by protease enzyme?

    <p>(+) ssRNA initiates direct translation into polyprotein.</p> Signup and view all the answers

    Study Notes

    • Viruses cannot metabolize or make energy, they are obligate intracellular parasites that use host cell machinery to replicate.
    • Viruses have a nucleic acid genome and a protein coating called a capsid, all components are derived from host cells.
    • Viruses cannot be killed, they are inactivated or neutralized, rendering them unable to infect.
    • Viruses come in a variety of sizes and families, each causing different diseases.
    • A virus is made up of a genome, capsid, and other structures like an envelope.
    • The genome contains the instructions to create new viral particles.
    • Capsid is the protective shell, built from many copies of one or several proteins.
    • The capsid plays a role in delivering nucleic acid into the host cell upon infection and releasing it at the right time.
    • Viral attachment proteins or spike glycoproteins are involved in binding to a cell receptor during infection.
    • Capsids can be icosahedral, helical, or complex in symmetry and shape.
    • Naked viruses do not have a lipid bilayer envelope.
    • Viral genomes can be DNA or RNA, single or double-stranded, linear, circular, or segmented/polyploid.

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    Test your knowledge on the structure and function of viruses, including their genome, capsid, and replication process, as well as how they infect host cells. Learn about the different types of viral families and their impact on causing diseases.

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