Viral Structure and Genome Quiz
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Questions and Answers

What is the diameter of naked icosahedral capsid of Picornaviruses?

  • ~20nm
  • ~50nm
  • ~40nm
  • ~30nm (correct)

    • How many copies of each of the three to four proteins are present in a mature Picornavirus virion?

  • 60 (correct)
  • 30
  • 50
  • 90

    • What is covalently bound to the 5’ end of the RNA in Picornaviruses?

  • Poly(A) tail
  • VP4
  • VPg (correct)
  • 5’ cap

    • What type of genome do Picornaviruses have?

    <p>'+' sense ssRNA</p> Signup and view all the answers

    What is the function of the Flavivirus E protein?

    <p>Directs receptor binding and membrane fusion</p> Signup and view all the answers

    What can antibody-dependent enhancement (ADE) cause in relation to flaviviruses?

    <p>More severe diseases like dengue hemorrhagic fever</p> Signup and view all the answers

    Where does RNA synthesis occur for Flaviviruses?

    <p>On membranes in the cytoplasm</p> Signup and view all the answers

    What is the role of the precursor membrane protein (prM) in Flaviviruses?

    <p>Associates with the E protein to form a heterodimer, protecting E from premature conformational changes</p> Signup and view all the answers

    What is the function of the NS3 protein in Flaviviruses?

    <p>Involved in polyprotein cleavage, RNA replicase component, nucleoside triphosphate, and helicase activities</p> Signup and view all the answers

    What is the mechanism of entry for Flaviviruses into cells?

    <p>Endocytosis within clathrin-coated vesicles</p> Signup and view all the answers

    What is the role of the poly(A) polymerases in viral translation?

    <p>They usually add the poly(A) tail encoded by the genome</p> Signup and view all the answers

    What is the function of the internal ribosome entry site (IRES) in the 5’ NCR?

    <p>It allows translation initiation without a 5’ cap</p> Signup and view all the answers

    What is the purpose of the pyrimidine rich track near AUG in IRES elements?

    <p>To imitate translation at the correct spot</p> Signup and view all the answers

    How does Picornavirus infection affect cap-dependent translation?

    <p>Causes proteolytic cleavage of eIF-4G, abolishing cap-dependent translation</p> Signup and view all the answers

    'Cleavage of VP0 to VP2 plus VP4' is associated with which stage of virion assembly?

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

    'Viral RNA is replicated after protein synthesis' involving what kind of complex bound to cellular vesicles?

    <p>'Complex bound to cellular vesicles'</p> Signup and view all the answers

    What is the diameter of the naked icosahedral capsid of Picornaviruses?

    <p>30nm</p> Signup and view all the answers

    What is covalently bound to the 5’ end of the RNA in Picornaviruses?

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

    What is the role of the internal ribosome entry site (IRES) in the 5’ NCR of Picornaviruses?

    <p>Facilitates cap-independent translation</p> Signup and view all the answers

    'Cleavage of VP0 to VP2 plus VP4' is associated with which stage of Picornavirus virion assembly?

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

    What is the function of the NS2B protein in Flaviviruses?

    <p>It is part of the viral proteinase that cleaves the viral polyprotein</p> Signup and view all the answers

    What is the role of the precursor membrane protein (prM) in Flaviviruses?

    <p>It associates with the E protein to form a heterodimer, protecting E from premature conformational changes</p> Signup and view all the answers

    Where does RNA synthesis occur for Flaviviruses?

    <p>In the cytoplasm on membranes</p> Signup and view all the answers

    What is antibody-dependent enhancement (ADE) capable of causing in relation to flaviviruses?

    <p>More severe diseases like dengue hemorrhagic fever, leading to organ failure and death if not treated</p> Signup and view all the answers

    'Viral RNA is replicated after protein synthesis' involving what kind of complex bound to cellular vesicles?

    <p>Active RNA replicase complexes</p> Signup and view all the answers

    What is the role of the poly(A) polymerases in viral translation?

    <p>Adding poly(A) tail to the viral genome</p> Signup and view all the answers

    What is the function of the internal ribosome entry site (IRES) in the 5’ NCR?

    <p>Allowing translation initiation without a 5’ cap</p> Signup and view all the answers

    'Cleavage of VP0 to VP2 plus VP4' is associated with which stage of virion assembly?

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

    'Picornavirus infection causes proteolytic cleavage of eIF-4G, abolishing cap-dependent translation' - How does this affect translation?

    <p>It abolishes cap-dependent translation</p> Signup and view all the answers

    'Flavivirus genome organization most resembles that of Picornaviruses' - How is the genome translated?

    <p>Into a single, long polyprotein that undergoes proteolytic processing</p> Signup and view all the answers

    'Viral RNA is replicated after protein synthesis' involving what kind of complex bound to cellular vesicles?

    <p>A multi-protein complex</p> Signup and view all the answers

    'IRES elements contain a pyrimidine rich track near AUG to imitate translation at the correct spot' - What is the purpose of this pyrimidine rich track?

    <p>To imitate translation at the correct spot</p> Signup and view all the answers

    'Entry of poliovirus RNA into the cytoplasm involves major rearrangement, forming a channel in the cell membrane' - What facilitates this entry?'

    <p>Major conformational change in viral capsid proteins</p> Signup and view all the answers

    'Virions bind to cellular receptors via ‘canyons’ or loop regions on their surface' - What is the significance of these 'canyons'?

    <p>They allow for specific binding to cellular receptors</p> Signup and view all the answers

    'Flavivirus virion contains an envelope and envelope proteins are arranged with icosahedral symmetry' - What does this arrangement facilitate?

    <p>Specific recognition by host cell receptors</p> Signup and view all the answers

    What is the role of the poly(A) tail in Picornavirus RNA?

    <p>It is encoded by the genome and normally acted upon by poly(A) polymerases</p> Signup and view all the answers

    What is the function of the internal ribosome entry site (IRES) in Picornaviruses?

    <p>Allows for translation at an internal site away from the 5’ end</p> Signup and view all the answers

    What is covalently bound to the 5’ end of the RNA in Picornaviruses?

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

    'Virions bind to cellular receptors via ‘canyons’ or loop regions on their surface' - What is the significance of these 'canyons'?

    <p>They allow for specific binding to cellular receptors</p> Signup and view all the answers

    What is the role of eIF-4G in the translation process during Picornavirus infection?

    <p>It is cleaved, abolishing cap-dependent translation in host cells</p> Signup and view all the answers

    What is the function of the 40S ribosomal subunit during Picornavirus infection?

    <p>It scans the mRNA to find the start codon (AUG)</p> Signup and view all the answers

    What facilitates the entry of poliovirus RNA into the cytoplasm?

    <p>VP4 and hydrophobic N-terminal of VP1 form a channel in the cell membrane</p> Signup and view all the answers

    What is the role of VPg in Picornavirus RNA synthesis?

    <p>It covalently binds to uridine residues, priming RNA synthesis</p> Signup and view all the answers

    What is the consequence of Picornavirus infection on host cell macromolecular functions?

    <p>Shut off host cap-dependent translation and RNA synthesis</p> Signup and view all the answers

    What is the mechanism by which newly synthesized virions are released from host cells?

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

    What is the role of VP0 during Picornavirus virion assembly?

    <p>It is cleaved into VP2 and VP4 to form mature virion</p> Signup and view all the answers

    What is the function of pentamers during Picornavirus virion assembly?

    <p>Pentamers and RNA assemble into provirion</p> Signup and view all the answers

    What is primed by VPg covalently bound to uridine residues during Picornavirus RNA synthesis?

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

    What facilitates capsid dissociation after endosomal acidification during Picornavirus infection?

    <p>VP1-4 folding into a jelly roll composed of an 8-stranded beta-barrel</p> Signup and view all the answers

    What is the diameter of naked icosahedral capsid of Picornaviruses?

    <p>~30nm</p> Signup and view all the answers

    What is covalently bound to the 5’ end of the RNA in Picornaviruses?

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

    What is the role of the internal ribosome entry site (IRES) in the 5’ NCR of Picornaviruses?

    <p>Allow initiation of translation without having a 5’ cap</p> Signup and view all the answers

    'Virions bind to cellular receptors via ‘canyons’ or loop regions on their surface' - What is the significance of these 'canyons'?

    <p>They facilitate binding to cellular receptors</p> Signup and view all the answers

    Study Notes

    Flavivirus and Togavirus Protein Structures and Functions

    • The NS3 protein is a vital serine proteinase involved in polyprotein cleavage, RNA replicase component, nucleoside triphosphate, and helicase activities, and is a non-structural protein.
    • The NS2B protein is part of the viral proteinase that cleaves the viral polyprotein.
    • The Flavivirus E protein directs receptor binding and membrane fusion, and it is a type I membrane protein found as a dimer, lying parallel to the lipid bilayer.
    • The synthesis of non-structural proteins establishes active RNA replicase complexes, and RNA synthesis occurs on membranes in the cytoplasm.
    • Flaviviruses do not have a clearly identified cellular receptor, and their entry is mediated by endocytosis within clathrin-coated vesicles.
    • Antibody-dependent enhancement (ADE) can cause more severe diseases like dengue hemorrhagic fever, leading to organ failure and death if not treated.
    • Once the genome is in the cytosol, the RNA is bound by ribosomes and translated, producing polyproteins that are cleaved to produce precursor/functional proteins.
    • The precursor membrane protein (prM) associates with the E protein in the endoplasmic reticulum (ER) to form a heterodimer, protecting E from premature conformational changes.
    • Togaviruses cause diseases in animals and humans, with symptoms ranging from rashes and high fever to joint pain and encephalitis.
    • Togaviruses have a spherical enveloped particle with a fringe of projections, with 240 heterodimers of glycoproteins E1 and E2 in the envelope and 240 copies of capsid proteins in the capsid.
    • Togaviruses have a linear '+' sense single-stranded RNA genome and four non-structural proteins translated directly from genomic RNA as a polyprotein.
    • The E glycoprotein binds to cellular receptors, such as the laminin receptor, leading to receptor-mediated endocytosis via clathrin-coated vesicles.

    Viral Translation and Replication Mechanisms

    • Poly(A) tail is encoded by the genome, but usually added by poly(A) polymerases
    • 5’ NCR contains an internal ribosome entry site (IRES) allowing translation initiation without a 5’ cap
    • IRES elements contain a pyrimidine rich track near AUG to imitate translation at the correct spot
    • Virions bind to cellular receptors via ‘canyons’ or loop regions on their surface
    • Picornavirus infection causes proteolytic cleavage of eIF-4G, abolishing cap-dependent translation
    • Picornavirus proteins are made as a single precursor polyprotein that is autocatalytically cleaved
    • Viral RNA is replicated after protein synthesis, involving a multi-protein complex bound to cellular vesicles
    • Entry of poliovirus RNA into the cytoplasm involves major rearrangement, forming a channel in the cell membrane
    • Virion assembly involves cleavage of VP0 to VP2 plus VP4, assembling into protomers and provirion
    • Picornavirus infection inhibits host cell functions, inducing cytoplasmic vesicles and altering intracellular transport pathways
    • Flavivirus virion contains an envelope and envelope proteins are arranged with icosahedral symmetry
    • Flavivirus genome organization most resembles that of Picornaviruses, translated into a single, long polyprotein that undergoes proteolytic processing

    Viral Translation and Replication Mechanisms

    • Poly(A) tail is encoded by the genome, but usually added by poly(A) polymerases
    • 5’ NCR contains an internal ribosome entry site (IRES) allowing translation initiation without a 5’ cap
    • IRES elements contain a pyrimidine rich track near AUG to imitate translation at the correct spot
    • Virions bind to cellular receptors via ‘canyons’ or loop regions on their surface
    • Picornavirus infection causes proteolytic cleavage of eIF-4G, abolishing cap-dependent translation
    • Picornavirus proteins are made as a single precursor polyprotein that is autocatalytically cleaved
    • Viral RNA is replicated after protein synthesis, involving a multi-protein complex bound to cellular vesicles
    • Entry of poliovirus RNA into the cytoplasm involves major rearrangement, forming a channel in the cell membrane
    • Virion assembly involves cleavage of VP0 to VP2 plus VP4, assembling into protomers and provirion
    • Picornavirus infection inhibits host cell functions, inducing cytoplasmic vesicles and altering intracellular transport pathways
    • Flavivirus virion contains an envelope and envelope proteins are arranged with icosahedral symmetry
    • Flavivirus genome organization most resembles that of Picornaviruses, translated into a single, long polyprotein that undergoes proteolytic processing

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