Microorganisms: Fungi and Viruses
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Questions and Answers

Which statement correctly describes the replication of RNA viruses?

  • RNA viruses replicate in the cytoplasm, except for influenza virus. (correct)
  • RNA viruses replicate in the nucleus.
  • RNA viruses do not require a host cell.
  • RNA viruses only replicate in a laboratory environment.

    • What is the primary role of decapsidation in viral replication?

  • It is the final step before the host cell lysis.
  • It synthesizes viral proteins and mRNA.
  • It is a preliminary stage that separates the virus from its infectious element. (correct)
  • It allows the viral genome to enter the host cell.

    • Which of the following statements about the morphogenesis stage is accurate?

  • Morphogenesis happens after the release of virions.
  • Viral inclusions are formed when excess viral components accumulate. (correct)
  • Morphogenesis only occurs in helical viruses.
  • It involves the synthesis of the viral genome only.

    • How do naked viruses typically release their virions from host cells?

    <p>By host cell lysis.</p> Signup and view all the answers

    What distinguishes DNA viruses in terms of their replication location compared to RNA viruses?

    <p>DNA viruses replicate in the nucleus, except for poxviruses.</p> Signup and view all the answers

    What is the bodily structure of filamentous fungi primarily composed of?

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

    Which fungi exists in both yeast and filamentous forms?

    <p>Histoplasma capsulatum</p> Signup and view all the answers

    What do naked viruses possess that contributes to their resistance to environmental factors?

    <p>A capsid</p> Signup and view all the answers

    Which type of viral infection can reactivate after a period of dormancy?

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

    What characteristic differentiates fungal organisms from bacteria?

    <p>Heterotrophic feeding mechanism</p> Signup and view all the answers

    What is a key structural feature of viruses?

    <p>A capsid and nucleic acid</p> Signup and view all the answers

    Parasites are categorized into two main types. Which of the following is not one of these categories?

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

    What is the common role of bacteriophages in bacterial ecosystems?

    <p>Gene transfer</p> Signup and view all the answers

    What characteristic makes naked viruses more resilient compared to enveloped viruses?

    <p>Greater resistance to external environmental factors</p> Signup and view all the answers

    Which stage of viral replication occurs immediately after the virus attaches to the host cell?

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

    What is the primary function of spike glycoproteins in viruses?

    <p>Attachment to host cell receptors</p> Signup and view all the answers

    Which of the following classifications is correct for a viral family?

    <p>Suffix -viridae</p> Signup and view all the answers

    During which stage of viral replication is infectivity lost?

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

    Which of the following is NOT a criterion for viral classification?

    <p>Symptomatic effects on host</p> Signup and view all the answers

    What is the process by which naked viruses typically enter host cells?

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

    What term describes the period from the entry of the virus into the host cell until the production of progeny virions?

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

    What characterizes enveloped viruses?

    <p>They have a lipid membrane acquired by budding through cell membranes.</p> Signup and view all the answers

    Which type of viral infection can be reactivated after a dormant phase?

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

    What is a key structural feature of T-phages?

    <p>They contain a helical tail with a rigid axial tube.</p> Signup and view all the answers

    What role do efflux pumps play in bacterial cells?

    <p>Expelling harmful substances and contributing to drug resistance.</p> Signup and view all the answers

    Which statement about the resolution limitations in microscopy for certain viruses is correct?

    <p>Viruses smaller than 100 nm cannot be observed using light microscopy.</p> Signup and view all the answers

    What defines a virulent phage?

    <p>It leads to lytic infection.</p> Signup and view all the answers

    What is the function of porins in gram-negative bacteria?

    <p>Transporting nutrients like iron and vitamins.</p> Signup and view all the answers

    In what way do latent infections differ from acute infections?

    <p>Latent infections can remain hidden for extended periods.</p> Signup and view all the answers

    Which class of the Coccidia phylum is known to have severe implications during pregnancy?

    <p>Toxoplasma gondii</p> Signup and view all the answers

    What is a defining characteristic of trematodes?

    <p>Dorso-ventrally flattened body</p> Signup and view all the answers

    Which of the following is a common feature of cestodes?

    <p>Absence of a digestive system</p> Signup and view all the answers

    What is the first intermediate host in the evolutionary cycle of trematodes?

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

    Which of the following nematodes is characterized by its spindle-shaped body?

    <p>Ascaris lumbricoides</p> Signup and view all the answers

    What is unique about schistosomes compared to other trematodes?

    <p>They are non-hermaphroditic</p> Signup and view all the answers

    Which part of a cestode is responsible for attachment to the host?

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

    Which of the following roundworms can cause significant human health issues?

    <p>Trichuris trichuria</p> Signup and view all the answers

    What role do arthropods play in disease transmission?

    <p>Acting as a vector</p> Signup and view all the answers

    Which term describes the reproductive system of cestodes?

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

    Study Notes

    Filmentous Fungi

    • Multicellular microorganisms
    • Composed of hyphae: tubular filaments, septate or not
    • Include: Aspergillus spp., Microsporum spp., Trichophyton spp., Epydermophyton floccosum

    Dimorphic Fungi

    • Microorganisms that occur in two forms:
      • Yeasts in tissues of parasitized organisms or at 37°C in vitro
      • Filamentous form when grown at room temperature or 30°C on normal media
    • Example: Histoplasma capsulatum

    Viruses

    • Very small infectious particles with no protein or energy synthesis capacity
    • Obligate intracellular parasites - Depend on host cells for replication
    • Contain a single type of nucleic acid (DNA or RNA), capsid, and sometimes an envelope
    • Naked viruses are more resistant to external factors than enveloped viruses
    • Replication occurs after attachment to specific host cell receptors
    • Viral infections can be:
      • Acute infections
      • Persistent infections: Chronic or latent, latent infections can reactivate
    • Bacteriophages are viruses that parasitize bacteria and play a role in gene transfer

    Parasites

    • Unicellular (protozoa) or Multicellular (helminths, arthropods) organisms

    Fungi

    • Microscopic
    • Eukaryotic
    • Unicellular or multicellular
    • Heterotrophic bioentities
    • Contain chitin in the cell wall

    Viral Structure

    • Envelope (lipid bilayer)
      • Contains glycoproteins:
        • hemagglutinins
        • receptors for Fc and C3b (in herpesviruses)
        • Enzyme (ex hyaluronidase)
        • Fusion with the host cell membrane
        • Point of attack for neutralizing antibodies
    • Naked viruses are more resistant to external environmental factors than enveloped viruses
    • Virion: Contains genome, matrix protein, spike glycoprotein

    Viral Taxonomy

    • Family: suffix "-viridae"
    • Subfamily: suffix "-virinae"
    • Genus: suffix "-virus"
    • Classification criteria:
      • Shape and size of the virus
      • Number and arrangement of capsomeres
      • Presence or absence of the envelope
      • Genome structure
      • Site and mode of replication
      • Antigenic structure
      • Sensitivity to physical and chemical agents

    Viral Replication

    • Viruses are replicated by living cells
    • Infectivity disappears from decapsidation of the virion to the appearance of progeny virions (eclipse period)
    • Stages:
      • Adsorption: Attachment of ligands to specific cell receptors (cell tropism)
      • Penetration:
        • Naked viruses: Receptor-dependent endocytosis
        • Enveloped viruses: Fusion of envelope with cytoplasmic membrane
        • Direct translocation of cell membrane (e.g., picornaviruses, papovaviruses) for small viruses
      • Decapsidation: Dissolution of the infectious element, RNA viruses replicate in the cytoplasm (except influenza virus), DNA viruses replicate in the nucleus (except poxviruses)
      • Synthesis of viral components: Viral genome (cellular/viral polymerases), mRNA, protein synthesis (Early = enzyme in general, Late = more specific)
      • Morphogenesis: Possible hollow icosahedral caps, never for those with helical symmetry, excess accumulated viral components → viral inclusions
      • Release of virions:
        • Naked Viruses: Host cell lysis
        • Enveloped viruses: Budding through modified cell membranes (viral glycoproteins)

    Evolution of Viral Infection

    • Resolution (represents antibodies)
    • Transformation (cancer)
    • Acute infection
    • Persistent infection:
      • Chronic infection
      • Latent infection: can be reactivated

    Bacteriophages

    • Viruses that parasitize bacteria
    • Similar in structure to animal viruses
    • T-phages are well-known:
      • Head: Nucleocapsid with icosahedral symmetry, containing dsDNA
      • Tail: Helical symmetry, includes a rigid axial tube, contractile sleeve, hexagonal base plate with tail fibres
    • Replication cycle in the bacterial cell is similar to viruses of medical interest

    Phage-Bacterial Cell Relationship

    • Virulent phage: Causes lytic infection (lytic phage)
    • Temperate phage: May integrate into the bacterial chromosome (lysogenic phage)
    • Phage therapy: Potentially used to treat bacterial infections

    Protozoa

    • Unicellular eukaryotic organisms
    • Lack cell walls
    • Classified into four main groups based on their means of locomotion:
      • Mastigophora (flagellates): Trypanosoma cruzi, Giardia lamblia, Trichomonas vaginalis
      • Sarcodina (amoebas): Entamoeba histolytica
      • Sporozoa (spore-forming): Plasmodium spp., Cryptosporidium spp., Toxoplasma gondii
      • Ciliate (mobile by cilia): Balantidium coli

    Helminths

    • Metazoa (multicellular animals)
    • Two phyla:
      • Plathelmintes (flatworms)
        • Flattened dorso-ventrally
        • Two classes:
          • Trematoda (flukes): Non-segmented, Fasciola hepatica
          • Cestoda (tapeworms): Segmented, Taenia spp., Echinococcus granulosus
      • Nemathelminthes (roundworms):
        • Spindle-shaped body
        • Differentiated genera: Ascaris lumbricoides, Enterobius vermicularis, Trichuris trichuria, Trichinella spiralis

    Trematodes (Flukes)

    • Flat, dorso-ventrally flattened, leaf-shaped worms
    • Exceptions: Schistosomes (thread-like)
    • Suckers for anchoring:
      • Mouth sucker: Around mouth opening, connected to oesophagus and intestine
      • Ventral sucker
    • Body surface forms a syncytial envelope for nutrient absorption
    • Most species are hermaphroditic, except schistosomes
    • Evolutionary cycle:
      • First intermediate host: Mollusc
      • Second intermediate host for some species: Arthropods and fishes

    Cestodes (Tapeworms)

    • Body consisting of:
      • Head (scolex)
      • Neck: Non-segmented proliferation zone
      • Body segments: Chain of segments (proglottids)
    • Hermaphroditic genitals
    • No digestive system (nutrients absorbed through the cuticle)
    • Evolutionary cycle: 1 or 2 intermediate hosts
    • Larval stages (metacestodes, cysticerci) can colonize human tissues and cause damage

    Nematodes (Roundworms)

    • Spindle-shaped, unsegmented, a few mm to 1 m long
    • External integument with complex structure
    • Internal organs: Digestive tract, reproductive organs
    • Central pseudo-coelomic cavity
    • Males smaller than females, genitals with species-typical characteristics

    Arthropods

    • Jointed limbs, symmetrical and chitinous body
    • Development by metamorphosis (successive molts)
    • Act as vectors for pathogen transmission by being involved in life cycles or carrying pathogens

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    Description

    This quiz covers key concepts related to filamentous fungi, dimorphic fungi, and viruses. Explore the characteristics, life cycles, and classifications of these microorganisms to test your understanding of microbiology. Perfect for students studying microbiology or related fields.

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