Viruses and their Repliction (Lec 10)
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Questions and Answers

Which of the following is the correct definition of a virion?

  • A diverse structure that varies widely in size, shape, and chemical composition
  • The extracellular form of a virus (correct)
  • A structure that allows the virus to travel from one host cell to another
  • A protein shell that contains the viral genome
  • What is the role of the capsid in a virion?

  • To contain the viral genome and allow for virus to travel from one host cell to the next (correct)
  • To arrange proteins in a precise and highly repetitive pattern
  • To provide a protective protein shell
  • To carry enzymes critical to successful infection and replication
  • Which type of virus contains an outer layer of protein plus lipid?

  • Naked virus
  • Enveloped virus (correct)
  • Bacteriophage
  • Rod-shaped virus
  • What determines the length and width of a rod-shaped virus?

    <p>The size and packaging of protein subunits</p> Signup and view all the answers

    What is the simplest number of capsomeres per face in a spherical virus with icosahedral symmetry?

    <p>3</p> Signup and view all the answers

    What is the primary component of the envelope in enveloped viruses?

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

    What are the five main steps of the viral life cycle?

    <p>Attachment, entry, synthesis, assembly, release</p> Signup and view all the answers

    Which enzyme forms a small pore in the peptidoglycan of the E. coli cell wall?

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

    What happens within a minute after T4 entry into a host cell?

    <p>Host DNA and RNA synthesis ceases</p> Signup and view all the answers

    Which proteins are encoded by the T4 genome and required for DNA replication?

    <p>Early proteins</p> Signup and view all the answers

    What happens during the middle phase of T4 infection?

    <p>Additional proteins that modify RNA polymerase are synthesized</p> Signup and view all the answers

    What is the term for the period following attachment during which infectious virions cannot be detected in the growth medium?

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

    How is the titer of infectious virions determined in a plaque assay?

    <p>By measuring the number of plaques on a lawn of host cells</p> Signup and view all the answers

    What is the term for the ability of a virus to alternate between a lytic pathway and a lysogenic pathway?

    <p>Temperate phage</p> Signup and view all the answers

    Which of the following best describes a virus?

    <p>A genetic element that can replicate only inside a living cell</p> Signup and view all the answers

    What is the size range of most viruses?

    <p>0.02 to 0.3 µm</p> Signup and view all the answers

    Which of the following is NOT a type of infection caused by viruses?

    <p>Protozoan infection</p> Signup and view all the answers

    What is the role of a host cell in virus replication?

    <p>Provide energy and metabolic intermediates for the virus</p> Signup and view all the answers

    Which of the following is NOT a characteristic of viral genomes?

    <p>They contain only two genes</p> Signup and view all the answers

    What happens during a lytic infection?

    <p>The virus redirects host metabolism to support replication and cause host cell death</p> Signup and view all the answers

    What is the consequence of a latent infection in animal cells?

    <p>Viral DNA does not replicate</p> Signup and view all the answers

    What is the consequence of a persistent infection in animal cells?

    <p>Release of virions by budding</p> Signup and view all the answers

    Where is most of Earth's genetic diversity found?

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

    What is the only viral genome that is able to translate immediately upon entering the host cell?

    <p>Postitive sense RNA</p> Signup and view all the answers

    What enzyme in retrovirus allows RNA to go to DNA?

    <p>Revers Transcriptase</p> Signup and view all the answers

    In retrovirus, the flow of genetic information after infection occurs in 'reverse'; that is, is flows from:

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

    Which is not an infection caused by animal cell viruses?

    <p>Lysogenetic Infection</p> Signup and view all the answers

    The process where virions come from budding of cell membrane without the final result of lysis of animal host cell is called what infection?

    <p>Persistent Infection</p> Signup and view all the answers

    Study Notes

    Viral Structure and Composition

    • A virion is a complete and infectious virus particle that consists of a genome surrounded by a protein shell called the capsid.
    • The capsid plays a crucial role in protecting the viral genome and facilitating the attachment of the virus to its host cell.

    Enveloped Viruses

    • Enveloped viruses possess an outer layer of protein plus lipid, known as the envelope, which is acquired from the host cell membrane during budding.

    Viral Shapes and Symmetry

    • The length and width of a rod-shaped virus are determined by the alignment of its protein subunits.
    • In a spherical virus with icosahedral symmetry, the simplest number of capsomeres per face is three.

    Viral Envelope

    • The primary component of the envelope in enveloped viruses is lipid bilayer, which is derived from the host cell membrane.

    Viral Life Cycle

    • The five main steps of the viral life cycle are: attachment, penetration, uncoating, replication, and lysis.

    Bacteriophage T4

    • The enzyme lysozyme forms a small pore in the peptidoglycan of the E. coli cell wall.
    • Within a minute after T4 entry into a host cell, the host cell's translation machinery is shut down.
    • The proteins encoded by the T4 genome and required for DNA replication are the T4 polymerase and helicase.
    • During the middle phase of T4 infection, the viral DNA is replicated, and the host cell's metabolism is altered to support viral replication.
    • The period following attachment during which infectious virions cannot be detected in the growth medium is known as the eclipse phase.

    Plaque Assay

    • The titer of infectious virions is determined in a plaque assay by counting the number of plaques formed on a lawn of host cells.

    Viral Infections

    • The ability of a virus to alternate between a lytic pathway and a lysogenic pathway is known as tropism.
    • A virus is a small infectious agent that requires a host cell to replicate.
    • The size range of most viruses is between 20-400 nanometers.

    Host Cell Role

    • The role of a host cell in virus replication is to provide the necessary machinery and resources for viral replication.

    Viral Genomes

    • One characteristic of viral genomes is that they are not capable of translating their genetic material into proteins immediately upon entering the host cell, except for the positive-sense RNA viruses.

    Types of Infections

    • A lytic infection results in the lysis of the host cell, whereas a latent infection in animal cells results in the integration of the viral genome into the host cell genome, allowing the virus to establish a long-term infection.
    • A persistent infection in animal cells results in the continuous production of viral particles without killing the host cell.
    • Plant viruses are not known to cause latent or persistent infections.

    Genetic Diversity

    • Most of Earth's genetic diversity is found in viruses.

    Retroviruses

    • The only viral genome that is able to translate immediately upon entering the host cell is the positive-sense RNA genome.
    • The enzyme reverse transcriptase in retroviruses allows RNA to be converted into DNA.
    • In retroviruses, the flow of genetic information after infection occurs in 'reverse', flowing from RNA to DNA.
    • Chronic infections are not caused by animal cell viruses.
    • The process where virions come from budding of cell membrane without the final result of lysis of the animal host cell is called a persistent infection.

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    Related Documents

    Virus Lecture Notes PDF

    Description

    Test your knowledge on the T4 bacteriophage life cycle and its interactions with E. coli cells. Learn about the lysozyme-like enzyme, DNA replication, transcription, translation, and more.

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