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Viruses Overview and Classification
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Viruses Overview and Classification

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@FoolproofLemur

Questions and Answers

Which of the following statements concerning viruses is FALSE?

  • Viruses enter a cell to complete the replication they have begun extracellularly. (correct)
  • Viruses never contain both DNA and RNA.
  • Tobacco mosaic virus was the first virus to be discovered and characterized.
  • Viral capsids can assume one of three basic shapes.
  • Some viruses have an outer membrane called an envelope.

    • The outermost layer of a virion fulfills which of the following functions of the virus?

  • Protection
  • Recognition and replication
  • Replication
  • Protection and recognition (correct)
  • Recognition

    • During the intracellular state, a virus exists as:

  • Both a lipid and a nucleic acid.
  • Both a protein and a nucleic acid.
  • A protein.
  • A lipid.
  • A nucleic acid. (correct)

    • Viruses are primarily classified according to their:

    <p>Type of nucleic acid.</p> Signup and view all the answers

    Host specificity of a virus is due to:

    <p>Interactions between viral and cellular surface molecules.</p> Signup and view all the answers

    Who was the first person to demonstrate the existence of viruses?

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

    How are fungal viruses different from viruses that infect other organisms?

    <p>They have no extracellular state.</p> Signup and view all the answers

    Which of the following infectious particles do NOT have protein in their structure?

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

    Which of the following would NOT be found as a component of a bacteriophage?

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

    Which of the following statements regarding virus taxonomy is true?

    <p>Some virus family names are derived from the name of an important member of the family.</p> Signup and view all the answers

    Which of the following statements comparing virus classification and taxonomy of organisms is true?

    <p>Genus and specific epithet are used in both classification systems.</p> Signup and view all the answers

    Put the following stages of a lytic replication cycle in order, from earliest to latest stages:

    <p>III, V, I, II, IV</p> Signup and view all the answers

    Which of the following is associated with the attachment of a bacteriophage to a bacterial cell?

    <p>Random collisions, chemical attractions, and receptor specificity</p> Signup and view all the answers

    The enzyme lysozyme is critical for which of the stages of a bacteriophage T4 infection cycle?

    <p>Entry and release</p> Signup and view all the answers

    The phenomenon of transduction is associated with which of the stages of a bacteriophage infection cycle?

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

    Which of the following events occurs in the lytic cycle of bacteriophage T4 infection but NOT in the lysogenic cycle?

    <p>Digestion of host DNA</p> Signup and view all the answers

    Why is lysogeny advantageous to a bacteriophage?

    <p>The genetic material of the bacteriophage can be passed on to future generations of cells.</p> Signup and view all the answers

    Which of the following agents is capable of inducing conversion of a prophage back to a lytic phage?

    <p>UV light and X rays</p> Signup and view all the answers

    Zones of clearing in cell cultures that are the result of virus infection are called plaques. What type of viral infection might cause cloudy plaques?

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

    Which of the following is matched INCORRECTLY?

    <p>Adenovirus — membrane fusion</p> Signup and view all the answers

    Reverse transcriptase is associated with which of the following?

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

    The genome of which of the following types of animal virus can act directly as mRNA?

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

    Which of the following types of animal virus requires RNA-dependent RNA transcriptase to be replicated?

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

    In contrast to most dsDNA animal viruses, the poxviruses replicate solely in the cytoplasm of the host cell. This fact implies that the viral genome may encode:

    <p>A DNA polymerase.</p> Signup and view all the answers

    Which of the following membranes can give rise to a viral envelope?

    <p>The nuclear and cytoplasmic membranes and the endoplasmic reticulum</p> Signup and view all the answers

    The majority of cases of infant diarrhea are caused by what kind of virus?

    <p>dsRNA viruses</p> Signup and view all the answers

    How is the HIV provirus different from a lambda phage prophage?

    <p>The HIV provirus is integrated permanently into the host cell's DNA.</p> Signup and view all the answers

    Which of the following individuals discovered prions?

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

    One mechanism by which viruses may cause cancer is to interrupt the genetic regulatory sequences of repressor proteins. Which of the following types of viruses is most likely to be involved in causing cancer by this mechanism?

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

    Tumors invade other organs and tissues in a process called:

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

    Plaque assays are used for:

    <p>Estimating the number of phages in a culture.</p> Signup and view all the answers

    Diploid cell cultures and continuous cell cultures differ in which of the following ways?

    <p>Longevity and source of cells</p> Signup and view all the answers

    Viroids infect:

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

    How are prions different from all other known infectious agents?

    <p>They lack nucleic acid.</p> Signup and view all the answers

    The infectious particles of fungi have RNA genomes and lack a capsid. They are therefore similar to:

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

    A lipid membrane is present in:

    <p>In both cells and viruses.</p> Signup and view all the answers

    Double-stranded DNA genomes are found in:

    <p>In both cells and viruses.</p> Signup and view all the answers

    Double-stranded RNA genomes can be found:

    <p>Only in viruses.</p> Signup and view all the answers

    Cytoplasm is a characteristic of:

    <p>Cells only.</p> Signup and view all the answers

    Proteins are present in:

    <p>Both cells and viruses.</p> Signup and view all the answers

    Viruses are shed slowly and steadily during:

    <p>Persistent infection.</p> Signup and view all the answers

    During __________, viruses remain dormant in a cell.

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

    Virus replication results in the death of the cell in a(n) __________ infection.

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

    Virus infection results in cancer in the process of __________.

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

    Is a mechanism of release for enveloped viruses.

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

    Viruses cause most human cancers.

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

    Most viruses cannot be seen by light microscopy.

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

    Protozoa are susceptible to viral attack.

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

    Many diseases of plants are caused by infectious RNA molecules lacking capsids.

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

    Bacteriophages are cheaper and easier to culture than animal viruses.

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

    Assembly of new viruses is a process that usually requires the direction of a variety of viral and cellular enzymes.

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

    Bacteriophage release is a gradual process in which small numbers are released at a time.

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

    Poxvirus is assembled in the cytoplasm of the cell instead of in the nucleus, as is the case for the majority of dsDNA viruses.

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

    Transcription of RNA from RNA does not occur in uninfected cells.

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

    Virus vaccines are always cultured in embryonated chicken eggs.

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

    Study Notes

    Viruses Overview

    • Viruses never contain both DNA and RNA; they either have one or the other.
    • Host specificity arises from interactions between viral surface molecules and cellular receptors.
    • Viruses are primarily classified by their type of nucleic acid: DNA or RNA.

    Virus Structure and Replication

    • The outer layer of a virion (virus particle) provides both protection and recognition functions.
    • The intracellular state of a virus is typically solely as nucleic acid, not as a protein or lipid.
    • Viral genomes, such as double-stranded DNA (dsDNA) and double-stranded RNA (dsRNA), are found in both viruses and cells.

    Virus Classification and Taxonomy

    • Virus family names may derive from significant members of the family rather than the host taxonomy.
    • The classification of viruses involves genus and species epithet, similar to organisms.

    Infection Mechanisms

    • Attachment of bacteriophages to bacterial cells involves random collisions, chemical attraction, and receptor specificity.
    • Bacteriophage infection leads to the lytic cycle, which involves stages: attachment, entry, synthesis, assembly, and release.

    Unique Viral Properties

    • Viroids lack protein and have RNA as their genetic material, differing from classical viruses.
    • Prions are unique infectious agents that consist solely of protein with no nucleic acids, causing neurological diseases.

    Cancer and Viral Infection

    • Certain viruses, notably retroviruses, can induce cancer by altering genetic regulatory sequences in host cells.
    • The process where tumors invade other tissues is termed metastasis.

    Viral Types and Their Effects

    • Positive-sense single-stranded RNA (+ssRNA) viruses can act directly as mRNA.
    • Negative-sense single-stranded RNA (-ssRNA) viruses require RNA-dependent RNA transcriptase for replication.

    Viral Lifecycle and Effects on Host Cells

    • Lytic infections result in cell death, while latent infections allow viruses to remain dormant.
    • Persistent infections involve slow and steady release of viruses over time, without immediate cell death.

    Methods of Study and Cultivation

    • Plaque assays are utilized to estimate the number of phages in a culture by observing zones of clearing.
    • Bacteriophages are more cost-effective and simpler to culture compared to animal viruses.

    Vaccination and Immune Response

    • Vaccines may be cultured in embryonated chicken eggs, although not exclusively.
    • Understanding the mechanism of virus assembly provides insights into potential therapeutic strategies.

    Additional Key Points

    • Most human cancers stem from viruses, highlighting the role of viral infections in oncology.
    • Many plant diseases are caused by RNA molecules that are infectious but lack protective capsids.

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    Description

    Explore the fascinating world of viruses, including their structure, replication, and classification. This quiz covers key concepts such as nucleic acid types, host specificity, and viral taxonomy. Test your knowledge of how viruses interact with host cells and their mechanisms of infection.

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