Viruses and Their Reproduction Cycles
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Questions and Answers

What are the two main components of a virus?

  • DNA and RNA only
  • Protein subunits and lipid layers
  • Genomic sequence and metabolic machinery
  • Outer capsid and inner core (correct)
  • Which cycle results in the death of the host cell immediately after virus release?

  • Enzootic cycle
  • Lysogenic cycle
  • Epizootic cycle
  • Lytic cycle (correct)
  • What is a reservoir species in the context of viruses?

  • A living host of a virus without causing disease (correct)
  • Any organism that carries a virus
  • A host that dies from the infection
  • An organism that spreads the virus between hosts
  • What is the purpose of spikes on a virus?

    <p>To attach to the host cell</p> Signup and view all the answers

    Which characteristic makes viruses different from living organisms?

    <p>Viruses cannot reproduce without a host.</p> Signup and view all the answers

    What is the primary difference between the lytic and lysogenic cycles?

    <p>The lytic cycle is faster than the lysogenic cycle.</p> Signup and view all the answers

    What triggers a virus in the lysogenic cycle to enter the lytic cycle?

    <p>Changes in environmental conditions</p> Signup and view all the answers

    In viral classification, what complicates the process compared to living organisms?

    <p>There is no common genomic sequence shared by all viruses.</p> Signup and view all the answers

    Which type of genome is found in a virus classified as type II in the Baltimore classification system?

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

    What characterizes the capsid structure of a naked icosahedral virus?

    <p>It is made up of protein subunits</p> Signup and view all the answers

    Which of the following examples is classified as a type IV virus?

    <p>Common cold</p> Signup and view all the answers

    In the Baltimore classification, how is mRNA produced for a type V virus?

    <p>Transcribed from the RNA genome</p> Signup and view all the answers

    What is a distinguishing feature of segmented genomes in virus classification?

    <p>They consist of multiple RNA molecules</p> Signup and view all the answers

    Which virus is an example of a type III virus according to the Baltimore classification?

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

    Which classification system was first developed by David Baltimore in the early 1970s?

    <p>Baltimore viral classification</p> Signup and view all the answers

    Non-segmented genomes in viruses typically indicate what kind of replication process?

    <p>The genome can be transcribed directly into mRNA</p> Signup and view all the answers

    What is the main reason anti-viral medications are difficult to develop?

    <p>They depend on the host's cellular machinery.</p> Signup and view all the answers

    Which of the following is true regarding viroids?

    <p>They consist only of naked strands of RNA.</p> Signup and view all the answers

    What is a common characteristic of prions?

    <p>They induce misfolding of normal proteins.</p> Signup and view all the answers

    Kuru is mainly associated with which cultural practice?

    <p>Cooked and consumed dead family members.</p> Signup and view all the answers

    Which of the following diseases is NOT caused by prions?

    <p>HIV.</p> Signup and view all the answers

    What is the role of reverse transcriptase in ssRNA viruses like HIV?

    <p>Synthesizes DNA from the RNA genome.</p> Signup and view all the answers

    Which of the following statements about dsDNA viruses is correct?

    <p>Their viral DNA is replicated through an RNA intermediate.</p> Signup and view all the answers

    Animal viruses can be classified primarily based on which aspect?

    <p>The type of genetic material they contain.</p> Signup and view all the answers

    What distinguishes a bacteriophage from other types of viruses?

    <p>They specifically attack bacterial cells.</p> Signup and view all the answers

    Which of the following is an example of an emerging virus?

    <p>COVID-19.</p> Signup and view all the answers

    How can emerging viruses spread to new locations?

    <p>Through air travel.</p> Signup and view all the answers

    Which of the following is NOT a characteristic of plant viruses?

    <p>They can infect human cells.</p> Signup and view all the answers

    What is a common feature of emerging diseases?

    <p>They can infect new species.</p> Signup and view all the answers

    Study Notes

    Viruses

    • Viruses are not considered to be living organisms, and they lack a cellular structure, which means they can't perform metabolic functions on their own
    • They're obligate intracellular parasites, meaning they require a host cell to replicate
    • The main components of a virus are a protein coat called the capsid and a core containing either DNA or RNA as its genetic material
    • Some viruses also possess spikes for attaching to host cells and an outer envelope
    • Viruses have a specific host cell that they infect
    • Once inside the host cell, the viral genome exploits the host's cellular machinery to produce more viruses
    • Viruses are unable to replicate independently and rely on a host cell for their survival

    Viral Reproduction Cycles

    • Lytic Cycle: The virus commandeers the host cell immediately, leading to the destruction of the infected cell and its membrane.
    • Lysogenic Cycle: The virus remains dormant until specific conditions trigger its entry into the lytic cycle.
    • Lytic Cycle Stages:
      • Absorption: Attachment of the virus to the host cell
      • Entry: Penetration of the virus into the host cell
      • Replication: Replication of the viral genome using host cell resources
      • Assembly: Formation of new viral particles
      • Release: Release of newly formed viral particles from the host cell, often leading to host cell death
    • Lysogenic Cycle:
      • The virus integrates its genetic material into the host cell's chromosome as a prophage
      • The phage remains dormant until a trigger activates its transition to the lytic cycle, resulting in replication, assembly, and release, ultimately killing the host cell

    Viral Classification

    • Classifying viruses is more intricate than classifying living organisms due to their diverse evolutionary origins.
    • Viruses are often described as "remnants" of other organisms, making traditional genomic or protein analysis less effective.
    • Viruses lack a common universally shared genomic sequence.
    • Previous classification methods included:
      • Genome structure: DNA vs RNA, single-stranded vs double-stranded, linear vs circular, non-segmented vs segmented genomes
      • Capsid structure: Naked icosahedral, enveloped icosahedral, enveloped helical, naked helical, complex with multiple proteins
    • Baltimore Classification: This method, named after Nobel laureate David Baltimore, classifies viruses based on their mRNA production methods during their replicative cycle.
      • Group I: dsDNA - mRNA is transcribed directly from DNA
      • Group II: ssDNA - DNA is converted to dsDNA before mRNA transcription
      • Group III: dsRNA - mRNA is transcribed from the RNA genome
      • Group IV: ssRNA (+) - Genome functions as mRNA
      • Group V: ssRNA (-) - mRNA is transcribed from the RNA genome
      • Group VI: ssRNA (reverse transcriptase) - Reverse transcriptase produces DNA from RNA, which is then integrated into the host genome; mRNA is transcribed from the incorporated DNA
      • Group VII: dsDNA (reverse transcriptase) - Viral DNA replicates through an RNA intermediate; RNA can serve as direct mRNA or a template for mRNA production

    Host Domain Viral Classification

    • Viruses can be categorized based on the types of hosts they infect:
      • Animal viruses: Viruses that infect animal cells, including humans (e.g., influenza virus, rabies virus, mumps virus, poliovirus). They typically have RNA or DNA genomes.
      • Plant viruses: Viruses that infect plants. Their genetic material is usually RNA, enclosed within a protein coat. (e.g., tobacco mosaic virus, potato virus, beet yellow virus, turnip yellow virus).
      • Bacteriophages: Viruses that infect bacterial cells. They typically contain DNA as their genetic material. Each bacteriophage usually attacks only one specific species or strain of bacteria.

    Emerging Viruses

    • Emerging viruses cause diseases that have recently infected large populations.
    • Examples include: COVID-19, HIV, West Nile virus, SARS virus, Hantavirus, Ebola virus, Avian influenza (H5N1) virus, Zika Virus.
    • They emerge through various mechanisms:
      • Transportation to new locations: Often facilitated by air travel
      • Infection of new species: Ability to infect a different host species
      • New modes of transmission: Development of novel transmission pathways

    Anti-Viral Medication

    • Developing anti-viral medication is challenging because viruses use their host's cellular machinery to replicate.
    • Some drugs are structurally similar to nucleotides, interfering with viral genome synthesis.
    • Other drugs target viral enzymes like reverse transcriptase in HIV.
    • Prevention is the most effective defense:
      • Vaccinations
      • Social distancing
      • Mask wearing

    Viroids

    • Exclusively infect plants
    • Consist of naked strands of RNA, not enclosed within a capsid
    • They take over the host cell to produce more viroids
    • Responsible for about a dozen crop diseases

    Prions

    • Proteinaceous infectious particles
    • Malformed proteins that convert normal proteins into more misshaped proteins
    • Discovered as the cause of kuru
    • Also responsible for mad cow disease (bovine spongiform encephalopathy) and Creutzfeldt-Jakob disease

    Kuru

    • A deadly prion disease that affected many people in Papua New Guinea
    • The disease was spread through the traditional practice of consuming the brains of deceased family members.
    • The brain was most likely to transmit kuru.

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    Description

    This quiz covers the nature of viruses, highlighting their non-living status and essential components such as the capsid and genetic material. It also explores the lytic and lysogenic reproduction cycles, providing insights into how viruses replicate inside host cells.

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