Introduction to Virology
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Questions and Answers

What is the primary function of the capsid in a virus?

  • To facilitate the entry of the virus into the host cell
  • To store energy for the virus
  • To enclose and protect the nucleic acid genome (correct)
  • To assist in the replication of the viral genome

    • Which of the following accurately describes enveloped viruses?

  • They have a lipid bilayer surrounding the capsid (correct)
  • They can only infect bacteria
  • They always exist in a lytic cycle
  • They lack a capsid structure

    • Which type of viral genome consists of both single-stranded and double-stranded forms?

  • Viruses with complex structures
  • Both DNA and RNA viruses (correct)
  • DNA viruses only
  • RNA viruses only

    • What differentiates a naked virus from an enveloped virus?

    <p>Naked viruses lack a lipid membrane surrounding the capsid</p> Signup and view all the answers

    During which cycle does a virus integrate its genome into the host's DNA and remain latent?

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

    What does the term 'obligate intracellular parasites' indicate about viruses?

    <p>They require host cells to replicate</p> Signup and view all the answers

    Which method of viral entry involves the virus tricking the host cell into engulfing it?

    <p>Receptor-Mediated Endocytosis</p> Signup and view all the answers

    Which type of viral capsid structure is characterized by 20 equilateral triangles?

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

    What is a common characteristic of all viruses?

    <p>They are made of nucleic acid and protein</p> Signup and view all the answers

    What role do glycoproteins fulfill in enveloped viruses?

    <p>They enable binding to host cells</p> Signup and view all the answers

    What is a defining characteristic of viruses that distinguishes them from living cells?

    <p>They require a host cell for replication.</p> Signup and view all the answers

    What component of a virus protects its genetic material?

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

    Which type of viral genome is characterized by having a single strand of nucleic acid?

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

    What distinguishes an enveloped virus from a naked virus?

    <p>Presence of a lipid bilayer</p> Signup and view all the answers

    In which viral replication cycle does the viral DNA remain dormant within the host cell?

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

    Which viral entry mechanism is characterized by the virus fusing with the host cell membrane?

    <p>Direct fusion</p> Signup and view all the answers

    What term describes the exchange of genetic material between two different viruses within a host cell?

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

    What type of virus structure involves viral proteins arranged in a way that forms a 20-sided shape?

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

    What best describes a bacteriophage's method of injecting genetic material into a host cell?

    <p>Injection by tail</p> Signup and view all the answers

    What is the purpose of glycoproteins found on the surface of some viruses?

    <p>To facilitate binding to host cell receptors</p> Signup and view all the answers

    What component is unique to enveloped viruses and absent in naked viruses?

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

    Which type of viral genome consists of either DNA or RNA but never both?

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

    What structure protects the viral genetic material and helps it survive outside the host cell?

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

    Which type of viral entry mechanism involves the use of host cell receptors for virus uptake?

    <p>Receptor-mediated endocytosis</p> Signup and view all the answers

    In which viral replication cycle do viruses proliferate and ultimately cause the host cell to lyse?

    <p>Lytic cycle</p> Signup and view all the answers

    What is the process by which segmented viruses exchange genetic material?

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

    Which capsid structure is specifically arranged helically to form a tube-like appearance?

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

    What type of viral genetic material is characterized by its double-stranded form?

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

    Which step is key in the transition from a lysogenic cycle to a lytic cycle?

    <p>Virus dormancy activation</p> Signup and view all the answers

    Which classification of viruses infects bacterial cells specifically?

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

    What is the primary feature that distinguishes a complex capsid structure from other types?

    <p>It combines both helical and icosahedral shapes.</p> Signup and view all the answers

    Which of the following accurately describes naked viruses?

    <p>They lack a lipid bilayer envelope.</p> Signup and view all the answers

    What characterizes the lytic cycle of viral replication?

    <p>New viral particles are produced, leading to host cell lysis.</p> Signup and view all the answers

    Which factor is NOT used to classify viruses?

    <p>Size of the virus</p> Signup and view all the answers

    Which type of viral genome is defined as containing circular forms?

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

    What distinguishes enveloped viruses from naked viruses in terms of structure?

    <p>Enveloped viruses have a lipid membrane.</p> Signup and view all the answers

    In viral entry, which mechanism involves exploiting host cell receptors?

    <p>Receptor-mediated endocytosis</p> Signup and view all the answers

    During which cycle does a virus replicate without killing the host cell?

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

    What is a common method by which bacteriophages inject their genetic material into host cells?

    <p>Tail injection</p> Signup and view all the answers

    Which of the following statements about glycoproteins in viruses is TRUE?

    <p>They assist with host cell attachment.</p> Signup and view all the answers

    What is the structure that consists of a viral genome protected by a protein coat?

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

    Which of the following best describes the lytic cycle?

    <p>Virus replicates to produce particles until the cell bursts</p> Signup and view all the answers

    What main factor is NOT used in the classification of viruses?

    <p>Geographical location of discovery</p> Signup and view all the answers

    Which type of viruses contain a lipid bilayer membrane?

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

    What is a common characteristic of segmented viral genomes?

    <p>Involved in reassortment</p> Signup and view all the answers

    What occurs during the lysogenic cycle of a virus?

    <p>Viral gene remains inactive within host DNA</p> Signup and view all the answers

    Which characteristic defines helical viruses?

    <p>Capsomeres in a tube-like arrangement</p> Signup and view all the answers

    Which method does a naked virus use to enter a host cell?

    <p>Receptor-mediated endocytosis</p> Signup and view all the answers

    What describes the role of glycoproteins within the viral envelope?

    <p>Facilitates recognition and binding to host cells</p> Signup and view all the answers

    What mechanism is primarily responsible for genetic exchange between viruses?

    <p>Recombination and reassortment</p> Signup and view all the answers

    What best describes the structure of a virus?

    <p>A protein coat surrounding either DNA or RNA.</p> Signup and view all the answers

    In which type of capsid structure are proteins arranged in a helical formation?

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

    What characteristic describes a virus with a lipid envelop?

    <p>It is known as an enveloped virus.</p> Signup and view all the answers

    Which viral infection method is common for enveloped viruses?

    <p>Direct fusion with the host cell membrane</p> Signup and view all the answers

    What type of virus specifically targets bacteria?

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

    Which term describes the phase where a virus replicates and causes the host cell to burst?

    <p>Lytic cycle</p> Signup and view all the answers

    What components are found in the nucleocapsid of a virus?

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

    What method do viruses commonly use to enter host cells?

    <p>Receptor-mediated endocytosis</p> Signup and view all the answers

    What is NOT a criterion used for classifying viruses?

    <p>Presence of wings</p> Signup and view all the answers

    What best defines the viral genome?

    <p>It can have either DNA or RNA but never both.</p> Signup and view all the answers

    What defines viruses as obligate intracellular parasites?

    <p>They can replicate only when infecting a host cell.</p> Signup and view all the answers

    Which best describes the composition of a virus's nucleocapsid?

    <p>The nucleic acid genome combined with the protein coat.</p> Signup and view all the answers

    What is a distinguishing feature of RNA viruses compared to DNA viruses?

    <p>They exclusively contain RNA as their genetic material.</p> Signup and view all the answers

    What feature differentiates complex viruses from helical and icosahedral viruses?

    <p>Complex viruses exhibit a combination of geometries.</p> Signup and view all the answers

    Which method of viral entry involves interaction with specific receptors on the host cell's surface?

    <p>Receptor-mediated endocytosis.</p> Signup and view all the answers

    During which viral cycle does the host cell eventually burst to release new virions?

    <p>Lytic cycle.</p> Signup and view all the answers

    What primary factor classifies viruses when considering their genome composition?

    <p>The type of nucleic acid and its strands.</p> Signup and view all the answers

    What characterizes enveloped viruses compared to naked viruses?

    <p>Enveloped viruses possess a lipid bilayer membrane.</p> Signup and view all the answers

    Which of the following best describes glycoproteins found on enveloped viruses?

    <p>They help the virus adhere to host cell receptors.</p> Signup and view all the answers

    Which viral attribute is essential for identifying the type of host a virus can infect?

    <p>Genome composition.</p> Signup and view all the answers

    Which mechanism of genetic exchange involves the combination of genetic material from segmented viruses?

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

    What is complementation in the context of viral interactions?

    <p>A functional virus providing components to a defective one</p> Signup and view all the answers

    What is NOT a characteristic of the lytic cycle?

    <p>Host cell remains intact during the cycle</p> Signup and view all the answers

    Which of the following best describes phenotypic mixing?

    <p>Exchange of protein capsids between two functional viruses</p> Signup and view all the answers

    What role does recombination play in viral genetics?

    <p>It involves exchange of genetic material between viruses</p> Signup and view all the answers

    Which best describes the condition of a dormant virus in the lysogenic cycle?

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

    What is the potential impact of reassortment in viruses?

    <p>It can lead to pandemics or epidemics</p> Signup and view all the answers

    What distinguishes lytic viruses from lysogenic viruses?

    <p>Lytic viruses replicate and lyse the host cell</p> Signup and view all the answers

    What is an example of a virus that utilizes complementation?

    <p>Hepatitis B assisting Hepatitis D</p> Signup and view all the answers

    What is the primary function of the viral nucleocapsid?

    <p>Protecting the genome from damage</p> Signup and view all the answers

    Which of the following correctly describes the characteristics of naked viruses?

    <p>They do not have an envelope</p> Signup and view all the answers

    What type of host do bacteriophages specifically infect?

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

    What is a key characteristic of the lytic cycle in viral multiplication?

    <p>Destruction of the host cell to release new viruses</p> Signup and view all the answers

    Which method allows enveloped viruses to enter host cells?

    <p>Endocytosis or direct membrane fusion</p> Signup and view all the answers

    What aspect of viral classification does genome geometry refer to?

    <p>The shape and arrangement of the genome</p> Signup and view all the answers

    Which viral feature aids in binding to receptor sites on host cells?

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

    What distinguishes a complex virus from helical and icosahedral viruses?

    <p>Unique combination of structural features</p> Signup and view all the answers

    Which statement accurately reflects the replication process of viruses?

    <p>Viruses require the host's cellular machinery to replicate</p> Signup and view all the answers

    What describes the process by which some viruses can remain dormant in host cells?

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

    What mechanism involves the exchange of segments of a viral genome between two virions?

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

    Which method allows a defective virus to gain missing components from a functional virus?

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

    What is the purpose of phenotypic mixing in viruses?

    <p>To swap capsid proteins between viruses</p> Signup and view all the answers

    Which characteristic about viruses is true regarding their classification?

    <p>Classification can include their structure and genome type.</p> Signup and view all the answers

    What does recombination in viruses refer to?

    <p>The exchange of genetic material from two viruses</p> Signup and view all the answers

    What is a major distinction between lytic and lysogenic cycles in viruses?

    <p>Lytic cycles always kill the host immediately.</p> Signup and view all the answers

    Which viral exchange mechanism does not involve the direct exchange of genetic material?

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

    What type of viruses use reassortment as a mechanism for genetic exchange?

    <p>Segmented genome viruses</p> Signup and view all the answers

    What role does capsid protein exchange play in phenotypic mixing?

    <p>It modifies host cell interactions.</p> Signup and view all the answers

    Which of the following statements is NOT true about viruses?

    <p>They can exist independently in nature.</p> Signup and view all the answers

    What defines the primary structure of a virus?

    <p>A nucleic acid genome and protein coat</p> Signup and view all the answers

    Which of the following accurately describes the lytic cycle of viral replication?

    <p>The host cell is ultimately destroyed after viral replication</p> Signup and view all the answers

    How are viruses classified based on their genome composition?

    <p>By type of nucleic acid and number of strands</p> Signup and view all the answers

    What is a key characteristic of naked viruses?

    <p>They lack an envelope surrounding the capsid</p> Signup and view all the answers

    What mechanism do envelope viruses primarily use to enter host cells?

    <p>Membrane fusion</p> Signup and view all the answers

    Which viral structure is described as having proteins arranged in a tube-like form?

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

    What occurs during the process of recombination in viruses?

    <p>Two viruses exchange genetic material within a host</p> Signup and view all the answers

    What distinguishes a icosahedral virus from a helical virus?

    <p>Icosahedral viruses form a spherical shape with triangular facets</p> Signup and view all the answers

    What is the primary consequence of a virus using the lytic cycle?

    <p>The host cell is lysed, releasing new viral particles</p> Signup and view all the answers

    In which replication cycle does viral genetic material integrate into the host's genome?

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

    Study Notes

    Introduction to Virology

    • Viruses are considered obligate intracellular parasites: they require a host cell to replicate.
    • They blur the line between living and non-living entities: they are not cells, but they can replicate and make proteins once inside a host cell.
    • Viruses are essentially genome packages made up of:
      • Nucleic acid genome: either DNA or RNA, but never both.
      • Protein coat (capsid): encloses the genome and protects it.
      • Nucleocapsid: capsid and genetic material together.
      • Envelope (optional): a lipid membrane surrounding the capsid.
      • Glycoproteins: on the envelope, used for binding to host cells.

    Virus Classification

    • Genome Composition:
      • Type of Nucleic Acid: DNA viruses or RNA viruses.
      • Number of Strands: Single-stranded or double-stranded DNA or RNA (but only one type at a time).
      • Genome Geometry: Linear or circular.
    • Capsid Structure:
      • Helical: Capsomers (proteins) arranged in a helical structure, forming a tube-like shape. Example: Tobacco mosaic virus.
      • Icosahedral: Capsomers form 20 equilateral triangles, creating a 20-sided diamond shape. Example: Poliovirus.
      • Complex: Combination of helical and icosahedral structures.
    • Presence of an Envelope:
      • Naked viruses: Lack an envelope.
      • Enveloped viruses: Possess a lipid bilayer envelope surrounding the capsid. Example: Influenza.
    • Type of Host:
      • Viruses can infect various organisms. Example: Bacteriophages (viruses that infect bacteria).
    • Method of Action: This can influence how a virus enters its host cell:
      • Tail Injection: Some viruses, particularly bacteriophages, have tail structures that inject their genetic material into a cell.
      • Direct Fusion: Enveloped viruses can fuse their lipid bilayer with the host cell membrane.
      • Receptor-Mediated Endocytosis: Naked or enveloped viruses can enter through host cell receptors, tricking the cell into engulfing them.

    Viral Replication Cycles

    • Lytic Cycle:
      • The virus uses the host cell's machinery to replicate and produce new viral particles.
      • Eventually, the host cell bursts (lyses) and releases the newly formed viruses.
    • Lysogenic Cycle:
      • The viral genome integrates into the host cell's genome and remains dormant (latent).
      • The host replicates its own genetic material, including the viral genome, producing more infected cells.
      • Under certain triggers, the latent viral genome can enter the lytic cycle, leading to virus production.

    Viral Genetic Exchange

    • Recombination: Two viruses exchange genetic material within a host cell.
    • Reassortment: Only in viruses with segmented genomes (e.g., influenza, bunyaviruses, orthomyxoviruses, arenaviruses, reoviruses), different segments of genetic material are exchanged between two viruses. This can lead to pandemics and epidemics.
    • Complementation: A functional virus provides missing components to a defective virus. Example: Hepatitis B providing an antigen to Hepatitis D.
    • Phenotypic Mixing: Two functional viruses exchange protein capsids, allowing for the transfer of viral characteristics even if the genetic material remains unchanged.

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    Description

    Explore the fascinating world of viruses in this quiz that covers their characteristics, replication, classification, and structure. Understand the differences between DNA and RNA viruses, as well as their complex architectures. Challenge your knowledge about how these obligate intracellular parasites interact with host cells.

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