Virology Fundamentals
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Questions and Answers

What is the estimated number of viruses on Earth?

  • 10^31 (correct)
  • 10^21
  • 10^41
  • 10^51

    • What is unique about the replication of viruses?

  • They replicate by independent synthesis of their constituent parts (correct)
  • They can replicate outside of host cells
  • They replicate by growth and division
  • They require no host cell to replicate

    • What is a key characteristic of viruses that distinguishes them from other microorganisms?

  • Their ability to grow and divide
  • Their ability to generate metabolic energy
  • Their ability to synthesize proteins
  • Their inability to replicate outside of host cells (correct)

    • What is the role of viruses in the aquatic world?

    <p>They move organic matter from particulate to dissolved</p> Signup and view all the answers

    What is an important function of viruses in evolution?

    <p>They transfer genes between bacteria in transduction</p> Signup and view all the answers

    What is a common component of all virions?

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

    What is the size range of virions?

    <p>10-400 nm in diameter</p> Signup and view all the answers

    What is the term for the protein coat of a virus?

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

    What is the term for sub-viral infectious agents that require a helper virus to replicate?

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

    What is the primary function of helical capsids in viral structures?

    <p>To aid in the transfer of genetic material between host cells</p> Signup and view all the answers

    What is the characteristic shape of icosahedral capsids?

    <p>A regular polyhedron with 20 equilateral faces and 12 vertices</p> Signup and view all the answers

    What is the term for the ring/knob-shaped units made of 5 or 6 protomers?

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

    What is the characteristic of pox viruses and large bacteriophages?

    <p>They do not fit into the category of having helical/icosahedral capsids</p> Signup and view all the answers

    What is the origin of animal virus envelopes?

    <p>Host cells' plasma/nuclear membranes</p> Signup and view all the answers

    What is the function of envelope proteins that project from the envelope surface?

    <p>To facilitate viral attachment to host cells</p> Signup and view all the answers

    What is the composition of viral genomes?

    <p>Either DNA or RNA, single or double stranded, segmented or circular</p> Signup and view all the answers

    What is the basis of the Baltimore classification system?

    <p>Viral genome structure and replication strategy</p> Signup and view all the answers

    What is the term for the viral particles that contain enzymes?

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

    What is the primary function of promoters in viral structures?

    <p>To self-assemble into capsids</p> Signup and view all the answers

    What is the characteristic shape of helical capsids?

    <p>Hollow tubes with protein walls</p> Signup and view all the answers

    What is the primary reason why viruses are incapable of replication outside host cells?

    <p>They lack the genetic information for metabolism.</p> Signup and view all the answers

    What is the role of the nucleocapsid in a virion?

    <p>It serves as a protein coat for the virus.</p> Signup and view all the answers

    What determines the size of a capsid?

    <p>The size of the nucleic acid</p> Signup and view all the answers

    What is the function of viral enzymes in the replication process?

    <p>To aid in the transcription and translation of viral genes</p> Signup and view all the answers

    What is the function of viruses in molecular biology?

    <p>They are sources of enzymes used in molecular biology.</p> Signup and view all the answers

    Which type of viral genome is composed of single-stranded DNA?

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

    What is the characteristic of virus multiplication?

    <p>They multiply by independent synthesis of their constituent parts.</p> Signup and view all the answers

    What is the estimated number of viruses on Earth?

    <p>10^31</p> Signup and view all the answers

    What is the role of spikes/peplomers in the viral life cycle?

    <p>To aid in viral attachment to host cells</p> Signup and view all the answers

    Which type of viral genome is characterized by reverse transcription?

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

    What is the purpose of spike proteins in some viruses?

    <p>To recognize and bind to host cells.</p> Signup and view all the answers

    What is the primary function of the envelope in viral structures?

    <p>To aid in viral attachment to host cells</p> Signup and view all the answers

    What is the function of viruses in the transfer of genes between bacteria?

    <p>They facilitate the transfer of genes through transduction.</p> Signup and view all the answers

    What is the characteristic of viral genomes that distinguishes them from other microorganisms?

    <p>Their composition of nucleic acid</p> Signup and view all the answers

    What is the term for sub-viral infectious agents that require a helper virus to replicate?

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

    What is the size range of virions?

    <p>10-400 nm in diameter</p> Signup and view all the answers

    Study Notes

    Viral Diversity and Characteristics

    • Estimated Number of Viruses on Earth: Millions of viruses are estimated to exist on Earth, significantly outnumbering all other life forms.
    • Viral Genome Composition: Viral genomes are composed of either DNA or RNA, but not both.
    • Viral Replication: Viruses are obligate intracellular parasites, meaning they can only replicate inside living host cells.
    • Viroid Characteristics: Viroids are sub-viral agents that lack a protein coat and require a helper virus for replication.
    • Viroid Size: Viroids are extremely small, typically ranging from 246 to 375 nucleotides in length.

    Viral Structure and Function

    • Capsid Function: The protein coat (capsid) of a virus protects the genetic material and facilitates attachment to host cells.
    • Capsid Types: Two primary types of capsids exist: helical and icosahedral.
    • Helical Capsids: Helical capsids exhibit a cylindrical or rod-shaped structure.
    • Icosahedral Capsids: Icosahedral capsids are characterized by a 20-sided symmetrical shape.
    • Capsomeres: Capsomeres are the building blocks of capsids, forming ring-shaped structures from 5 or 6 protein subunits called protomers.
    • Envelope Function: Viral envelopes aid in attachment to host cells and can be acquired from the host cell membrane during viral budding.
    • Envelope Proteins: Envelope proteins extend from the envelope surface and play a vital role in viral attachment and entry into host cells.
    • Nucleocapsid: The nucleocapsid is the viral capsid along with the nucleic acid genome.
    • Importance of Viral Enzymes: Some viruses contain enzymes within their particles called virions. These enzymes, like reverse transcriptase or lysozyme, are critical for replication.

    Viral Replication and Evolution

    • Viral Replication: Viruses multiply inside host cells by exploiting the host's cellular machinery to produce new virions.
    • Viral Replication Steps: Viral replication involves several steps, including:
      • Attachment: Binding to host cells.
      • Entry: Penetration into the host cell.
      • Replication: Production of new viral components.
      • Assembly: Formation of new virions.
      • Release: Egress from the host cell.
    • Viral Evolution: Viruses are incredibly adaptable and can evolve rapidly.
    • Viral Influence on Evolution: Viruses play a crucial role in gene transfer between bacteria, contributing to genetic diversity.

    Viral Classification and Impact

    • Baltimore Classification: Viruses are classified based on their genomic architecture and replication strategies, as outlined by the Baltimore Classification System.
    • Reverse Transcription: Some viruses, like retroviruses, utilize reverse transcription to convert RNA into DNA.
    • Viral Impact: Viruses are responsible for a wide range of human diseases, from the common cold to more severe illnesses.

    Additional Key Points

    • Viral Sizes: Virions (virus particles) vary in size, ranging from 20 to 400 nanometers in diameter.
    • Viral Function: Viruses can have beneficial roles, such as promoting gene transfer and influencing evolutionary processes.

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    Test your knowledge of viruses, their structure, replication, and impact on disease and the environment. Learn about the importance of viruses in the aquatic world and their role in evolution.

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