Viral Nucleic Acid and Types
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Questions and Answers

What factor is used to classify viruses into enveloped and non-enveloped categories?

  • Presence or absence of a viral envelope (correct)
  • The morphology of the virus
  • The geographic location of the discovery
  • The type of genetic material present

    • Which of the following characteristics best describes enveloped viruses?

  • They have a rigid protein shell
  • They are derived from the host cell membrane (correct)
  • They are robust in extreme environmental conditions
  • They transmit easily through air

    • What is one reason why enveloped viruses require close contact for transmission?

  • They require host enzymes for activation
  • They can only be transmitted through vectors like mosquitoes
  • They can replicate only inside specific cells
  • Their lipid membranes are easily damaged by environmental factors (correct)

    • Which type of nucleic acid do adenoviruses and herpesviruses have?

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

    Why is the classification of viruses based on their envelope considered important?

    <p>It affects how they interact with host cells</p> Signup and view all the answers

    What type of genetic material is found in filamentous phages like M13?

    <p>Circular single stranded DNA</p> Signup and view all the answers

    Which feature is characteristic of T-even phages?

    <p>Icosahedral head and a complex tail structure</p> Signup and view all the answers

    How do filamentous phages like M13 interact with their host without killing them?

    <p>By budding from the host cell</p> Signup and view all the answers

    What size is the capsid head of lambda phages?

    <p>50-60 nm in diameter</p> Signup and view all the answers

    Which of the following statements is true about spherical phages?

    <p>They attach to the host without the aid of a tail assembly.</p> Signup and view all the answers

    Which viral class requires conversion to dsDNA before replication?

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

    Which type of RNA virus can act directly as mRNA?

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

    In which site do most dsDNA viruses replicate?

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

    Which of the following examples belongs to the -ssRNA viruses?

    <p>Rabies virus</p> Signup and view all the answers

    What characterizes ssRNA viruses that have a DNA reverse transcription step?

    <p>Integrates into the host genome</p> Signup and view all the answers

    Which viral class is distinguished by packaging RNA polymerase for transcription?

    <p>-ssRNA</p> Signup and view all the answers

    What is the primary replication site for the dsRNA viruses?

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

    How are the RNA reverse transcribing viruses classified?

    <p>RNA reverse transcribing viruses</p> Signup and view all the answers

    What type of nucleic acid do most DNA viruses possess?

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

    How do RNA viruses primarily replicate their genomes?

    <p>In the cytoplasm using their own enzymes</p> Signup and view all the answers

    What is a characteristic feature of ssRNA viruses?

    <p>Their RNA can act directly as mRNA.</p> Signup and view all the answers

    Which enzyme is typically brought by RNA viruses for replication?

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

    What occurs to the genome of the HIV virus after it enters a host cell?

    <p>It integrates into the host genome.</p> Signup and view all the answers

    Which type of viral genome requires conversion to dsDNA before replication?

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

    Where do most dsDNA viruses replicate their genome?

    <p>In the nucleus using host DNA polymerase</p> Signup and view all the answers

    What structural component is made up of protein subunits called capsomeres?

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

    Which type of virus likely requires packaging of RNA polymerase for transcription?

    <p>Negative-sense single-stranded RNA virus</p> Signup and view all the answers

    Which characteristic is typical for dsRNA viruses such as Rotavirus?

    <p>They require conversion to dsDNA before replication.</p> Signup and view all the answers

    Which of the following viruses causes highly contagious airborne respiratory illness?

    <p>Influenza virus</p> Signup and view all the answers

    Which family of viruses is characterized by having a bullet shape and includes the rabies virus?

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

    What type of RNA do paramyxoviruses have?

    <p>Linear, nonsegmented, negative-polarity RNA</p> Signup and view all the answers

    Which virus is known to cause severe hemorrhagic fevers?

    <p>Ebola virus</p> Signup and view all the answers

    What is the structure of coronaviruses?

    <p>Enveloped virus with a helical nucleocapsid and positive-polarity RNA</p> Signup and view all the answers

    Which of the following viruses is part of the lentivirus group?

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

    Which statement about filoviruses is true?

    <p>They are long threadlike viruses causing severe hemorrhagic fevers.</p> Signup and view all the answers

    What type of nucleocapsid do rhabdoviruses possess?

    <p>Helical nucleocapsid</p> Signup and view all the answers

    Study Notes

    Viral Nucleic Acid

    • Viral genomes direct the production of proteins and nucleic acids within the host cell.
    • DNA viruses utilize the host cell's replication machinery for replication.
    • RNA viruses typically bring their own enzymes, such as RNA-dependent RNA polymerase, for replication.
    • Viral nucleic acid is used to create viral mRNA, which is then translated into viral proteins by the host cell's ribosomes.
    • The replication process differs based on whether the virus contains DNA or RNA.
    • Some viruses, like HIV, integrate their genome into the host's genome.

    Types of Viral Nucleic Acid

    • Viruses are classified by their nucleic acid type.
    • DNA viruses are further categorized into single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA).
    • ssDNA viruses must be converted to dsDNA before replication.
    • dsDNA is the most common type of DNA genome found in viruses.
    • Most DNA viruses replicate their genome within the host cell nucleus using the host's DNA-dependent DNA polymerase for DNA synthesis and RNA polymerase for transcription.
    • Some larger DNA viruses, like poxviruses, replicate in the cytoplasm using their own viral enzymes.
    • RNA viruses primarily replicate in the host cell's cytoplasm.
    • RNA viruses often use their own RNA-dependent RNA polymerase because host cells lack the necessary enzymes to replicate RNA from an RNA template.

    Comparison of Viral Genome Types

    • dsDNA: Herpesviruses, Adenoviruses - Stable genomes, rely on host DNA polymerase, can establish latent infections - Replication in the nucleus (mostly)
    • ssDNA: Parvoviruses - Requires conversion to dsDNA before replication - Replication in the nucleus
    • dsRNA: Rotavirus - Requires conversion to dsDNA before replication - Replication in the cytoplasm
    • +ssRNA: Poliovirus, SARS-CoV 2 - RNA can act directly as mRNA - Replication in the cytoplasm
    • -ssRNA: Influenza, rabies virus - Must package RNA polymerase for transcription of RNA - Replication in cytoplasm and nucleus
    • ssRNA with DNA intermediate: HIV - RNA reverse transcribed into DNA, integrates into host genome - Replication in cytoplasm and nucleus
    • Reverse transcribing DNA (dsDNA and RNA intermediate): Hepatitis B virus - DNA replicates via RNA - Replication in cytoplasm and nucleus

    Capsid

    • The capsid is a vital structural component of viruses, composed of protein subunits called capsomeres.
    • The capsid protects the viral genome and helps in viral attachment to host cells.

    Classification of Viruses

    • Viruses can be classified based on:
      • The disease they cause (e.g., poliovirus, rabies virus)
      • The type of disease (e.g., murine leukemia virus)
      • Geographic location (e.g., Sendai virus, Coxsackie virus)
      • Their discoverers (e.g., Epstein-Barr virus)
      • How they were originally thought to be contracted (e.g., dengue virus, influenza virus)
      • Combinations of the above (e.g., Rous Sarcoma virus)

    Classification of Viruses Based on Presence or Absence of Envelope

    • Enveloped viruses have a lipid bilayer membrane surrounding their capsid, acquired from the host cell during budding.
      • They are sensitive to environmental conditions like heat, detergents, and desiccation due to the fragile lipid bilayer.
      • They often require close contact for transmission.
    • Non-enveloped viruses lack this membrane.
      • They are more resistant to environmental factors.

    The Baltimore Classification System

    • This system categorizes viruses based on their genetic material and replication strategies into seven classes:
      • dsDNA viruses
      • ssDNA viruses
      • dsRNA viruses
      • (+) sense ssRNA viruses (codes directly for protein)
      • (-) sense ssRNA viruses
      • RNA reverse transcribing viruses
      • DNA reverse transcribing viruses

    T-Even Phages

    • T-phages are a specific class of bacteriophages, including T4 and T7, that infect E. coli.
    • They have an icosahedral head, double-stranded DNA, and a tail with a sheath, base plate, and tail fibers.
    • Their replication cycle involves:
      • Attachment to the bacterium
      • Insertion of genetic material
      • Replication
      • Lysis of the bacterium
      • Release of new viruses

    Temperate Phages

    • Lambda phages have an icosahedral head, a flexible non-contractile tail, and a single, double-stranded DNA molecule.
    • They can integrate their genome into the host's genome, leading to lysogeny.

    Filamentous Phages

    • M13 is a filamentous bacteriophage with circular single-stranded DNA.
    • It attaches to the F pilus of E. coli and does not kill the host.
    • New viruses are released by budding.

    Spherical Phages

    • Bacteriophage phiX174 is an icosahedral phage that attaches to the host cell without a tail.
    • It has a protein coat surrounding a core containing DNA and proteins.
    • RNA phages include phages with RNA genomes, such as:
      • Human T-cell leukemia virus (HTLV)
      • Lentivirus group, including human immunodeficiency virus (HIV)

    Orthomyxoviridae

    • These are enveloped viruses with eight segments of linear, single-stranded, negative polarity RNA.
    • They cause highly contagious airborne respiratory illnesses, with influenza virus being the primary human pathogen.

    Paramyxoviridae

    • Enveloped viruses with a helical nucleocapsid.
    • Single-stranded, linear, nonsegmented, negative-polarity RNA.
    • They include measles, mumps, parainfluenza, and respiratory syncytial viruses.

    Rhabdoviridae

    • Bullet-shaped enveloped viruses with a helical nucleocapsid.
    • Single-stranded, linear, nonsegmented, negative-polarity RNA.
    • They infect mammals, reptiles, fish, insects, and plants.
    • Rhabdoviruses infecting mammals are grouped into two genera:
      • Vesiculovirus – containing vesicular stomatitis virus and related viruses like chadipura virus (arbovirus)
      • Lyssavirus – containing rabies virus and related viruses
    • Rabies virus is a significant human pathogen.

    Filoviridae

    • Long threadlike viruses with a helical nucleocapsid.
    • Single-stranded, linear, nonsegmented, negative-polarity RNA.
    • Highly pleomorphic, long filaments.
    • The two human pathogens are Ebola virus and Marburg virus, causing severe hemorrhagic fevers.

    Coronaviridae

    • Enveloped viruses with a helical nucleocapsid.
    • Single-stranded, linear, nonsegmented, positive-polarity RNA.
    • They have a prominent halo of spikes protruding from the envelope.
    • Coronaviruses cause respiratory tract infections, such as the common cold, SARS, and COVID-19.
    • Two genera found under this family:
      • Coronavirus
      • Torovirus

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    Medical Microbiology Techniques III (ML 302) Unit 2 PDF

    Description

    Explore the fascinating world of viral nucleic acids and their role in the life cycle of viruses. This quiz covers the differences in replication processes between DNA and RNA viruses, as well as the various types of viral nucleic acids. Test your understanding of how these genetic materials influence viral behavior and classification.

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