BIOL212 W6-1
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Questions and Answers

What is the size range difference between the smallest and largest viral genomes?

  • 100-fold
  • 50-fold
  • 1000-fold (correct)
  • 2000-fold

    • What is the typical size characteristic of RNA viral genomes compared to DNA viral genomes?

  • Variable and unpredictable compared to DNA viruses
  • Typically smaller than DNA viruses (correct)
  • Approximately the same size as DNA viruses
  • Typically larger than DNA viruses

    • What is the size of the smallest known circovirus genome?

  • ~3800 nucleotides
  • ~1700 nucleotides
  • ~1.75 kilobases (correct)
  • ~2 megabases

    • Which organism is known to harbor both bacteria and viruses, including those pathogenic to humans?

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

    Pandoravirus infects which type of organism?

    <p>Marine amoebae</p> Signup and view all the answers

    What type of genetic material do the majority of known circoviruses possess?

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

    Which of the following diseases is associated with porcine circoviruses?

    <p>Post-weaning Multisystemic Wasting Syndrome (PMWS)</p> Signup and view all the answers

    Which class of viruses primarily infects plants according to the Baltimore classification?

    <p>Class VII (dsDNA)</p> Signup and view all the answers

    What type of proteins are synthesized early during viral infection?

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

    Which statement is true regarding the phylogenetic infection capabilities of different virus classes?

    <p>Class IV viruses are devoid of prokaryotic hosts.</p> Signup and view all the answers

    What significant transition might viruses have contributed to in early biological evolution?

    <p>Transition from RNA to DNA</p> Signup and view all the answers

    Which viral class is mostly comprised of prokaryotic viruses?

    <p>Class I (dsDNA)</p> Signup and view all the answers

    What defines a Class I virus in the Baltimore scheme?

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

    Which class of viruses includes those that replicate through a DNA intermediate?

    <p>Class VI</p> Signup and view all the answers

    Which class of viruses is characterized by having a genome that functions directly as mRNA?

    <p>Class IV</p> Signup and view all the answers

    What is a requirement for single-stranded positive-strand DNA viruses to replicate?

    <p>They need a double-stranded DNA intermediate</p> Signup and view all the answers

    How do class V viruses generate their mRNA?

    <p>RNA replicase synthesizes mRNA from their RNA genome</p> Signup and view all the answers

    In the Baltimore scheme, what characterizes class III viruses?

    <p>They have double-stranded RNA</p> Signup and view all the answers

    What is the role of reverse transcriptase in retroviruses?

    <p>To convert RNA to DNA</p> Signup and view all the answers

    Which class of viruses does not have a double-stranded DNA stage in their life cycle?

    <p>Class IV</p> Signup and view all the answers

    Which class of viruses consists primarily of positive-strand single-stranded RNA?

    <p>Class IV</p> Signup and view all the answers

    What is a common feature of Class V RNA viruses?

    <p>They use a negative-strand RNA template for mRNA synthesis</p> Signup and view all the answers

    What characteristic of bacteriophage M13 allows it to cause chronic infections without cell lysis?

    <p>It can exit the cell without lysing the host.</p> Signup and view all the answers

    Which feature of bacteriophage T7 is important for its interaction with host cells?

    <p>The encoding of T7 RNA polymerase for efficient replication.</p> Signup and view all the answers

    What is the primary method of genome replication utilized by the bacteriophages mentioned?

    <p>Rolling circle replication.</p> Signup and view all the answers

    Which of the following accurately describes the structural composition of the virion of bacteriophage T7?

    <p>Made of 60 asymmetric protein units organized in a cubical structure.</p> Signup and view all the answers

    What role does the ability to inhibit peptidoglycan synthesis play in the lifecycle of bacteriophages?

    <p>It leads to cell lysis and the release of new virions.</p> Signup and view all the answers

    Which feature is unique to the ATV virus in Acidianus?

    <p>Develops without host cell contact</p> Signup and view all the answers

    What distinguishes SSV and SIFV viruses from others?

    <p>SSV has spindle-shaped virions while SIFV has helical rods</p> Signup and view all the answers

    What is the primary replication location for pox viruses?

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

    What is a notable consequence of smallpox infection?

    <p>It leads to extensive skin scarring</p> Signup and view all the answers

    Which of the following statements about vaccinia virus is true?

    <p>It is a model for studying smallpox</p> Signup and view all the answers

    What type of viruses have not been isolated but are suggested to exist through environmental genomics?

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

    What is the approximate genome size of the vaccinia virus?

    <p>~190 kbp</p> Signup and view all the answers

    What is the role of the Mu transposase in the lifecycle of Bacteriophage Mu?

    <p>It helps in the integration of the phage into the host genome.</p> Signup and view all the answers

    Which aspect distinguishes the temperate nature of Bacteriophage Mu?

    <p>It alternates between lytic and lysogenic cycles.</p> Signup and view all the answers

    Which statement is true regarding the genome of Bacteriophage Mu?

    <p>It is linear and encodes proteins for both cycles.</p> Signup and view all the answers

    What characteristic allows Bacteriophage Mu to infect specific bacterial hosts?

    <p>The type of tail fibers it possesses.</p> Signup and view all the answers

    What is the fate of the host cell during the lytic cycle of Bacteriophage Mu?

    <p>The host cell lyses and releases mature virions.</p> Signup and view all the answers

    How does integration of Bacteriophage Mu into the host genome affect bacterial genetics?

    <p>It generates mutations that can be used for genetic studies.</p> Signup and view all the answers

    Which of the following best describes the replication process of Bacteriophage Mu?

    <p>It involves repeated transposition to different sites in the host genome.</p> Signup and view all the answers

    What distinguishes the archaeal viruses discussed from those that infect bacteria?

    <p>They are primarily enveloped and single-stranded DNA viruses.</p> Signup and view all the answers

    What is a consequence of the integration of SV40 virus DNA into the host genome in nonpermissive hosts?

    <p>Loss of contact inhibition leading to malignancy</p> Signup and view all the answers

    What is the significance of the large T antigen produced by SV40 in the context of tumor suppression?

    <p>It inhibits the function of tumor suppressor proteins pRb and p53.</p> Signup and view all the answers

    Which of the following is a common characteristic of herpesviruses?

    <p>They can establish latency and reactivate under certain conditions.</p> Signup and view all the answers

    How do herpesviruses initiate infection upon attachment to a host cell?

    <p>Host cytoplasmic membrane fuses with the viral envelope.</p> Signup and view all the answers

    During herpesvirus replication, which class of mRNA is produced first and what is its primary function?

    <p>Immediate early mRNA; it encodes regulatory proteins for viral gene expression.</p> Signup and view all the answers

    What percentage of patients undergoing allogeneic transplantation develop CMV disease?

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

    What is the primary method by which the MS2 bacteriophage infects E. coli?

    <p>By attaching to the pilus</p> Signup and view all the answers

    Which characteristic is unique to the positive-strand RNA of bacteriophage MS2?

    <p>It directly functions as mRNA.</p> Signup and view all the answers

    What is the consequence of herpes simplex virus being transmitted through direct contact?

    <p>Symptoms may only develop when the immune system is weakened.</p> Signup and view all the answers

    What role does RNA replicase play in bacteriophage MS2 replication?

    <p>It converts positive RNA into negative RNA.</p> Signup and view all the answers

    What is a common health condition linked to herpes simplex virus according to recent studies?

    <p>Alzheimer's disease</p> Signup and view all the answers

    How does spontaneous assembly of bacteriophage MS2 occur during its lifecycle?

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

    What disease is primarily associated with Epstein-Barr virus (EBV)?

    <p>Infectious mononucleosis</p> Signup and view all the answers

    Which condition significantly increases the risk of developing Burkitt's lymphoma in children in Africa?

    <p>Malaria co-infection</p> Signup and view all the answers

    What is a frequent complication for organ transplant recipients regarding cytomegalovirus (CMV)?

    <p>Serological mismatch between donor and recipient</p> Signup and view all the answers

    In which cells does Epstein-Barr virus establish latency?

    <p>B-lymphocytes</p> Signup and view all the answers

    Which statement is true regarding Epstein-Barr virus transformation?

    <p>It is complex and may involve multiple viral genes.</p> Signup and view all the answers

    What is the approximate genome size of cytomegalovirus?

    <p>235 kb</p> Signup and view all the answers

    What viral disease category is most closely linked with the development of nasopharyngeal carcinoma (NPC)?

    <p>Epstein-Barr virus</p> Signup and view all the answers

    What mechanism is suggested to contribute to the oncogenic transformation of B-cells by Epstein-Barr virus in individuals with malaria?

    <p>Weakening of the immune system</p> Signup and view all the answers

    What must the rabies virus do before it can be replicated within the host cell?

    <p>It must first be transcribed by viral replicase.</p> Signup and view all the answers

    Which of the following is a consequence of the segmented genome of the influenza virus?

    <p>It enables antigenic shift through reassortment.</p> Signup and view all the answers

    Which enzyme is NOT associated with the rabies virus's replication process?

    <p>Human rabies immune globulin</p> Signup and view all the answers

    What is the immediate treatment recommended for a person exposed to rabies?

    <p>Immediate postexposure prophylaxis (PEP).</p> Signup and view all the answers

    What structural feature does the influenza virus possess?

    <p>It has an enveloped and non-uniform morphology.</p> Signup and view all the answers

    What is one purpose of the neuraminidase protein in the influenza virus?

    <p>It assists in the breakdown of host cell membrane components.</p> Signup and view all the answers

    How can rabies disease be mitigated in pets?

    <p>Through regular vaccination of pets.</p> Signup and view all the answers

    What critical role does the RNA replicase play in the lifecycle of a negative-strand RNA virus?

    <p>Converts the viral genome into mRNA.</p> Signup and view all the answers

    What is a primary consequence of the complex assembly process of viruses like rabies and influenza?

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

    What is a major factor contributing to the outbreaks caused by hybrid virions?

    <p>Absence of immunity to new forms</p> Signup and view all the answers

    Which of the following influenza viruses is associated with high fatality rates in humans?

    <p>H5N1</p> Signup and view all the answers

    Which class of viruses primarily infects a variety of organisms, including animals, plants, and fungi?

    <p>Double-Stranded RNA Viruses</p> Signup and view all the answers

    What global pandemic was caused by H1N1 influenza?

    <p>Spanish Flu</p> Signup and view all the answers

    Which genetic characteristic is unique to segmented viruses like influenza A?

    <p>Multiple distinct RNA segments</p> Signup and view all the answers

    What is a principal consequence of zoonotic influenza A viruses for human health?

    <p>They can cause sudden outbreaks due to population immunity gaps.</p> Signup and view all the answers

    Which virus is known to cause diarrhea primarily in infants aged 6-24 months?

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

    In terms of fatality, which influenza virus poses the highest risk based on recent data?

    <p>H5N1</p> Signup and view all the answers

    What is a common clinical manifestation of infections caused by dual-stranded RNA viruses?

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

    What factor makes close contact between animals and humans a concern for viral outbreaks?

    <p>Increases likelihood of zoonotic spillover</p> Signup and view all the answers

    What function does the viral tRNA serve in the retroviral replication process?

    <p>It acts as a primer for DNA synthesis.</p> Signup and view all the answers

    Which components do retroviruses incorporate into their virions?

    <p>Viral tRNA, reverse transcriptase, and the RNA genome.</p> Signup and view all the answers

    What distinguishes hepadnaviruses from retroviruses in their replication mechanism?

    <p>Hepadnaviruses employ a protein primer for DNA synthesis.</p> Signup and view all the answers

    What characteristic distinguishes PrPSc from PrPC?

    <p>PrPSc has a different conformation.</p> Signup and view all the answers

    Which mechanism allows PrPSc to cause disease in hosts?

    <p>By converting PrPC into PrPSc.</p> Signup and view all the answers

    What are long terminal repeats (LTRs) and their significance in retroviral genomes?

    <p>They assist in the integration of viral DNA into the host genome.</p> Signup and view all the answers

    In retroviral infection, which of the following could happen to the viral DNA after integration?

    <p>It can remain latent or be expressed to produce new virions.</p> Signup and view all the answers

    In what way does the accumulation of PrPSc affect the nervous system?

    <p>It leads to the destruction of brain tissue.</p> Signup and view all the answers

    Which of the following diseases is associated with prions?

    <p>Chronic wasting disease</p> Signup and view all the answers

    What is a key characteristic of the genome of hepadnaviruses?

    <p>It features a double-stranded DNA genome with overlapping genes.</p> Signup and view all the answers

    How is the host range of prion diseases primarily determined?

    <p>By the amino acid sequence of the prion protein.</p> Signup and view all the answers

    What is a significant consequence of chronic Hepatitis B Virus (HBV) infection?

    <p>Development of Hepatocellular carcinoma (HCC)</p> Signup and view all the answers

    What form does the HBV genomic DNA take after the nucleocapsid enters the host nucleus?

    <p>Double-stranded covalently closed circular DNA (cccDNA)</p> Signup and view all the answers

    Which aspect of HBV contributes to the challenge in controlling infections?

    <p>Presence of incomplete vaccination coverage</p> Signup and view all the answers

    What is the primary function of reverse transcriptase in the life cycle of HBV?

    <p>Synthesis of genomic DNA from RNA template</p> Signup and view all the answers

    Which population is most significantly affected by chronic HBV infections worldwide?

    <p>Approximately 250 million individuals globally</p> Signup and view all the answers

    What initiates RNA transcription during the HBV life cycle?

    <p>Transformation of viral DNAs into cccDNA</p> Signup and view all the answers

    What vaccine technology related to HBV was transferred to China in 1993?

    <p>Technology for recombinant HBsAg production</p> Signup and view all the answers

    What factor complicates the effectiveness of vaccination programs against HBV since the 1980s?

    <p>Inclusion of chronic carriers and incomplete vaccination coverage</p> Signup and view all the answers

    What is a primary effect of HBV on liver health?

    <p>Development of liver cirrhosis</p> Signup and view all the answers

    Which population demographic contains a significant number of people already chronically infected with HBV?

    <p>Residents in China</p> Signup and view all the answers

    Study Notes

    Viral Genome Size and Structure

    • Viral genomes vary greatly in size, ranging from ~1000-fold from smallest to largest
    • Smallest viruses are circoviruses, with genome sizes of 1.75-kilobases (kb)
    • Largest viruses are Pandoraviruses, with genomes of 2.5-megabases (Mb)
    • Pandoraviruses infect marine amoebae
    • Some RNA viruses are smaller than DNA viruses
    • Viral genomes are diverse and vary enormously in size.

    Largest Virus - Pandoravirus

    • Pandoraviruses are parasitic in amoebae found in water
    • Their micrometer-sized ovoid particles contain DNA genomes of at least 2.5 megabases
    • These genomes contain around 2500 genes

    Amoeba and Viruses

    • Amoeba are unicellular organisms that alter their shape and reside in environments like water
    • Amoeba can host bacteria that cause human disease, like Legionella

    Smallest Virus - Circovirus

    • Porcine circoviruses are the most extensively studied
    • They have single-stranded circular DNA genomes of ~1700-3800 nucleotides (nt)
    • These genomes only encode three genes
    • Porcine circoviruses can cause post-weaning multisystemic wasting syndrome (PMWS) and porcine dermatitis and nephropathy syndrome (PDNS)
    • Animal vaccines are available for these diseases.

    The Baltimore Scheme of Viruses

    • Developed by David Baltimore, recognizing the relationship between a virus's genome and its produced mRNA.
    • The scheme classifies viruses into seven classes based on the genetic materials of these viruses.
      • Class I: Double-stranded DNA viruses
      • Class II: Single-stranded DNA viruses
      • Class III: Double-stranded RNA viruses
      • Class IV: Single-stranded (+)RNA viruses
      • Class V: Single-stranded (-)RNA viruses
      • Class VI: Single-stranded (+)RNA retroviruses
      • Class VII: Double-stranded DNA viruses that replicate through a transcript of RNA
    • Different classes have different methods of replication and mRNA production. 

    Baltimore Scheme: DNA Viruses

    • Focused on the relationship of the genome to mRNA, seven classes of viruses are defined.
    • Class I: Double-stranded DNA viruses
    • Class II: Single-stranded DNA viruses (most single-stranded DNA viruses have positive-sense DNA)
    • Replicative form of a single-stranded DNA virus is a double-stranded DNA molecule

    Baltimore Scheme: RNA Viruses

    • Class IV: Single-stranded positive-sense RNA viruses; genome is directly translated into mRNA
    • Class V: Single-stranded negative-sense RNA viruses: RNA replicase converts the negative-sense RNA into positive-sense RNA to be translated into proteins
    • Class III: Double-stranded RNA viruses; replication is similar to class V
    • Class VI: Single-stranded RNA retroviruses; use reverse transcriptase to convert RNA into DNA for incorporation into the host genome
    • Class VII: Double-stranded DNA viruses; replicate via an RNA intermediate.

    Baltimore Scheme: Host

    • Specific viral classes infect particular phylogenetic lineages
    • Class I (dsDNA) primarily infect prokaryotes
    • Class IV (ss(+)RNA) primarily infect eukaryotes
    • Fungi are typically infected by classes III and IV viruses
    • Most Class I and V viruses infect animals, while some also infect plants
    • Class VI (retroviruses) infect only animals

    Viral Protein Synthesis

    • Early proteins, primarily enzymes, are produced soon after infection
    • These early proteins help shut down host processes (ex: transcription and translation)
    • Late proteins (structural and assembly proteins) are synthesized later
    • New virions are assembled and released by lysis or budding.

    Viral Evolution

    • Viruses likely emerged after cells
    • They may have arisen from cellular remnants, or as integral components of the RNA world
    • They could also be early forms of life
    • Hypothesis: Viruses arose as mechanisms to rapidly transfer genetic material

    Proteomics and Viral Appearance

    • Proteomics suggests viruses originated from ancient cells
    • These cells had segmented RNA genomes, arising before the last universal common ancestor (LUCA)
    • Evolutionary pressure to reduce cell/genome size likely led to the protein shell and host reliance
    • RNA viruses are potentially older than DNA viruses

    Viral Phylogeny

    • Phylogenetic trees of viruses are based on protein sequences and structural features
    • RNA viruses preceded DNA viruses, contributing to the three domains of life
    • Few viral groups have assembled trees from shared genes/proteins
    • Examples include nucleocytoplasmic large DNA viruses (NCLDV) like Mimivirus

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    Description

    Explore the fascinating world of viral genome sizes and structures in this quiz. Learn about the smallest and largest viruses, their genetic composition, and their relationships with amoebae. Test your knowledge on viral genome diversity and the unique characteristics of circoviruses and Pandoraviruses.

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