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Questions and Answers
Which type of viral structure is characterized by a flexible filament and contains a helical tube around the genome?
Which type of viral structure is characterized by a flexible filament and contains a helical tube around the genome?
- Amorphous virus
- Filamentous virus (correct)
- Complex-tailed bacteriophage
- Icosahedral virus
What is a defining characteristic of complex-tailed bacteriophages?
What is a defining characteristic of complex-tailed bacteriophages?
- Their genetic material is only RNA.
- They are amorphous with spike proteins.
- They have no envelope.
- They inject genetic material into host cells. (correct)
Which virus is known for its ability to rapidly mutate, leading to new strains that evade immune recognition?
Which virus is known for its ability to rapidly mutate, leading to new strains that evade immune recognition?
- Ebola virus
- Smallpox virus
- Herpes simplex virus
- Influenza virus (correct)
Which statement about viral genome size is accurate?
Which statement about viral genome size is accurate?
What is the role of spike proteins in enveloped viruses?
What is the role of spike proteins in enveloped viruses?
What type of viruses lack a symmetrical form and typically have a flexible core structure?
What type of viruses lack a symmetrical form and typically have a flexible core structure?
What distinguishes the Baltimore Classification system of viruses?
What distinguishes the Baltimore Classification system of viruses?
Which of the following structures is NOT part of the virus structure summary?
Which of the following structures is NOT part of the virus structure summary?
Which category of viruses specifically targets bacterial cells?
Which category of viruses specifically targets bacterial cells?
What component may be present in some viruses and is involved in reverse transcription?
What component may be present in some viruses and is involved in reverse transcription?
What is the primary factor that largely determines a virus's host range and tissue tropism?
What is the primary factor that largely determines a virus's host range and tissue tropism?
Which characteristic does NOT describe the Baltimore classification model of viruses?
Which characteristic does NOT describe the Baltimore classification model of viruses?
What is one reason why antiviral agents are hard to discover?
What is one reason why antiviral agents are hard to discover?
Which of the following best describes the role of the capsid in a virus?
Which of the following best describes the role of the capsid in a virus?
What type of symmetry is exhibited by viruses with an icosahedral capsid?
What type of symmetry is exhibited by viruses with an icosahedral capsid?
What is a significant distinction between DNA and RNA viral genomes?
What is a significant distinction between DNA and RNA viral genomes?
Which subtype of viruses is classified based on the presence or absence of an envelope?
Which subtype of viruses is classified based on the presence or absence of an envelope?
Which type of virus structure is characterized by having 20 identical triangular faces?
Which type of virus structure is characterized by having 20 identical triangular faces?
What can be said about the evolution rate of viruses compared to bacteria?
What can be said about the evolution rate of viruses compared to bacteria?
What is NOT a function of the viral envelope structure?
What is NOT a function of the viral envelope structure?
What distinguishes viruses from living cells?
What distinguishes viruses from living cells?
Which class of viral genomes is known for being made up entirely of RNA?
Which class of viral genomes is known for being made up entirely of RNA?
What is the term used to describe the range of hosts a virus can infect?
What is the term used to describe the range of hosts a virus can infect?
Which of the following accurately describes the Virus-First Model of virus origin?
Which of the following accurately describes the Virus-First Model of virus origin?
Which characteristic is NOT typically associated with viruses?
Which characteristic is NOT typically associated with viruses?
What is tissue tropism in relation to viruses?
What is tissue tropism in relation to viruses?
In the Reduction Model of virus origin, viruses are thought to have:
In the Reduction Model of virus origin, viruses are thought to have:
Which component is a major structural element of all virions?
Which component is a major structural element of all virions?
Viruses are known to infect which of the following groups of organisms?
Viruses are known to infect which of the following groups of organisms?
What is the primary distinction between the Escape Model and the Reduction Model regarding virus origin?
What is the primary distinction between the Escape Model and the Reduction Model regarding virus origin?
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Study Notes
Viruses and Their Nature
- Viruses are ubiquitous, infecting all forms of life, including bacteria, archaea, and eukaryotes.
- They cause significant diseases in humans, such as influenza and the common cold.
- Viruses are obligate intracellular parasites, meaning they can only replicate within a host cell.
- They are distinct from cells as they lack ribosomes and other components necessary for independent life.
- Viral infection leads to viral replication, which can result in host cell death or debilitating effects.
Viral Genomic Diversity
- Viral genomes are composed of either DNA or RNA, which can be single- or double-stranded.
- The Baltimore classification system groups viruses based on their genome type, strand, and replication strategy.
- The capsid protects the viral genome outside of the host cell.
- Some viruses also have an envelope derived from the host membrane, studded with viral envelope proteins.
Viral Structure and Diversity
- Viral structure varies, with three main categories: icosahedral, filamentous, and complex.
- Icosahedral capsids have radial symmetry, forming a polyhedron with 20 identical triangular faces (e.g., herpes simplex virus).
- Filamentous viruses have helical symmetry, generating a flexible filament (e.g., Ebola virus).
- Complex viruses have a complex structure not easily categorized, often with a flexible "core wall" containing genetic material and a viral envelope with spike proteins (e.g., smallpox virus).
Viral Genome Size and Evolution
- RNA viruses generally have smaller genomes compared to DNA viruses.
- Some viruses, like retroviruses, have RNA genomes, while others like herpes simplex virus have large DNA genomes.
- Viruses evolve quickly due to antigenic drift, where rapid mutations lead to new strains that are not recognized by existing antibodies.
- This constant evolution necessitates repeated immunizations for viruses like influenza.
The International Committee on Taxonomy of Viruses (ICTV)
- Classifies viruses based on multiple factors, including:
- Capsid form (icosahedral or filamentous).
- Envelope (present or absent).
- Host range.
Host Range and Tissue Tropism
- Host range refers to the species a virus can infect.
- Tissue tropism describes the specific tissues a virus can infect within a host.
- Both factors are determined by the availability of suitable receptor molecules on the host cell surface.
Challenges in Antiviral Drug Discovery
- Antiviral drug discovery is complex and challenging due to:
- The requirement for specific virus-encoded proteins to commandeer host metabolism.
- The difficulty in targeting viral proteins without causing harm to the host.
- The rapid mutation rate of viral genomes, making drug resistance a constant threat.
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