Virus Infection and Replication Quiz
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Questions and Answers

What is the primary purpose of virus replication?

  • To create new, infectious virions (correct)
  • To eliminate host cell functions
  • To enhance viral protein stability
  • To integrate into the host genome

    • In which stage of the virus replication cycle does the capsid break down?

  • Release
  • Uncoating (correct)
  • Attachment
  • Penetration

    • Which of the following statements about virus assembly is correct?

  • Virions are replicated through cell division
  • Virion assembly occurs only after maturation
  • Virion assembly always requires a host cell nucleus
  • Virions are assembled de novo from components (correct)

    • What role do co-receptors play in the virus attachment process?

    <p>They serve as initial binding points for some viruses</p> Signup and view all the answers

    Which of the following stages is NOT required by all viruses in the replication cycle?

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

    What determines the tropism of a virus?

    <p>The specific proteins on the virus surface</p> Signup and view all the answers

    Which method is used by enveloped viruses to enter host cells?

    <p>Membrane fusion with host cell membranes</p> Signup and view all the answers

    Why are transgenic mice expressing CD155 important for studying poliovirus?

    <p>They can become infected like humans</p> Signup and view all the answers

    What is a key characteristic of viruses that can undergo cell-cell membrane fusion?

    <p>They can infect multiple cells at once</p> Signup and view all the answers

    What hinders the effectiveness of vaccines against certain viruses like HIV?

    <p>The virus hides inside cells during infection</p> Signup and view all the answers

    What is the primary function of uncoating in the virus replication cycle?

    <p>Release of the virus genome into the cell</p> Signup and view all the answers

    Which type of viruses must transport their genomes into the nucleus?

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

    Which genome type typically requires RNA polymerases for gene transcription?

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

    Which of the following viral genomes does NOT require entry into the nucleus for replication?

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

    What replication strategy does the viral genome follow?

    <p>Is dependent upon the type of nucleic acid genome it possesses</p> Signup and view all the answers

    What distinguishes dsRNA viruses from RNA viruses that reverse transcribe?

    <p>dsRNA viruses have a segmented genome</p> Signup and view all the answers

    Which of the following statements is true regarding parvoviruses?

    <p>They replicate their single-stranded DNA in a unique manner</p> Signup and view all the answers

    What type of genomes can viral genomes possess?

    <p>Both linear and circular genomes</p> Signup and view all the answers

    How do RNA viruses cope with monocistronic mRNA limitations?

    <p>By using a polyprotein that is cleaved into individual proteins</p> Signup and view all the answers

    What is the primary function of an internal ribosome entry site (IRES) in RNA viruses?

    <p>To enable cap-independent translation of multiple genes</p> Signup and view all the answers

    Why are RNA viruses more prone to mutations compared to DNA viruses?

    <p>RNA-dependent RNA polymerases lack proofreading ability</p> Signup and view all the answers

    What is the role of scaffolding proteins during the assembly of RNA viruses?

    <p>They provide a framework for the assembly of the mature capsid</p> Signup and view all the answers

    Which of the following statements correctly describes the packaging signal in RNA viruses?

    <p>It is a short RNA sequence recognized by packaging proteins</p> Signup and view all the answers

    During which stage of the viral replication cycle does the maturation of the virus occur?

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

    What distinguishes the mutation rates of RNA viruses from those of DNA viruses?

    <p>DNA replication has higher error correction capabilities</p> Signup and view all the answers

    What is the role of reverse transcriptase in retroviruses?

    <p>To transcribe viral RNA into DNA</p> Signup and view all the answers

    What is the role of the viral protease in the maturation of HIV?

    <p>To cleave the Gag polyprotein into functional proteins</p> Signup and view all the answers

    What is the primary process by which enveloped viruses escape from an infected cell?

    <p>Budding from the cell membrane</p> Signup and view all the answers

    In the context of virus replication, what does the term 'eclipse period' refer to?

    <p>The period when infectious viruses are not released from the cell</p> Signup and view all the answers

    What is the burst size in a virus growth curve?

    <p>The number of viruses released per infected cell</p> Signup and view all the answers

    Which characteristic is typically true regarding defective viral particles?

    <p>They have a higher ratio of non-infectious to infectious particles</p> Signup and view all the answers

    How does lysis of a cell differ from budding in the context of viral release?

    <p>Budding is a process where cell membranes are minimally affected</p> Signup and view all the answers

    What does the multiplicity of infection (MOI) indicate?

    <p>The ratio of infectious virions to cells</p> Signup and view all the answers

    Which factor is essential for the curving of membranes in enveloped virus release?

    <p>Presence of viral surface proteins</p> Signup and view all the answers

    Study Notes

    Virus Infection and Replication

    • Virus must replicate to create new virions for continued infection.
    • Replication involves breaking down the virion capsid, releasing the genome, and assembling new particles.
    • Virions assemble de novo, unlike the process in cell division.

    Virus Replication Cycle

    • Involves seven stages: attachment, penetration, uncoating, replication, assembly, maturation (some viruses), and release.
    • These stages may not occur in a strict order.

    Attachment

    • Involves viral binding to host cell at the plasma membrane through specific receptors.
    • Some viruses, like HIV, require co-receptors for effective binding.
    • Virus attachment specificity influences the tropism (host range) of the virus.
    • Example: Poliovirus requires CD155 for infection; transgenic mice expressing CD155 can be infected.

    Penetration

    • The virus crosses the plasma membrane using various methods.
    • Enveloped viruses typically enter through membrane fusion; some also employ cell-to-cell transmission.
    • Vaccine challenges arise as viruses can evade antibodies when hidden inside cells.

    Uncoating

    • Release of the viral genome via capsid breakdown occurs through various mechanisms.
    • Some viruses transport their genomes into the nucleus, often at the nuclear envelope.

    Replication

    • Viral genome replication varies by nucleic acid type (DNA or RNA).
    • Genome categorization: dsDNA, ssDNA, dsRNA, +ssRNA, -ssRNA, and retroviruses.
    • DNA viruses usually enter the nucleus to utilize host machinery, except poxviruses, which replicate in the cytoplasm.
    • RNA viruses utilize strategies like polyproteins and Internal Ribosome Entry Sites (IRES) for protein synthesis.
    • RNA viruses have higher mutation rates than DNA viruses due to the lack of proofreading capability in RNA-dependent RNA polymerases.

    Assembly and Maturation

    • Assembly involves the formation of a mature virion around scaffolding proteins and viral DNA.
    • Maturation includes proteolytic cleavage of viral proteins, necessary for virion infectiousness.
    • Example: HIV Gag polyprotein is cleaved post-release to form an infectious particle.

    Release

    • Nascent virions escape the infected cell, typically through budding for enveloped viruses.
    • Budding involves viral protein interactions with cellular membranes, forming the viral envelope.
    • Non-enveloped viruses generally exit via cell lysis.

    Virus Growth Curves

    • One-step growth curves track the replication cycle parameters.
    • Multiplicity of Infection (MOI) defines the number of viral particles per cell.
    • Key phases include the eclipse period (no released particles) and latent period (time with no infectious release).
    • Burst size indicates the total number of virions released from each cell.

    Defective Viral Particles

    • The ratio of non-infectious to infectious particles is typically higher than 10, indicating many released particles are non-infectious (defective).

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    Description

    Test your knowledge on the stages of virus infection and replication. This quiz covers the key processes involved, including attachment, penetration, and the overall replication cycle of viruses. Understand how viruses interact with host cells and the implications of these interactions.

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