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Questions and Answers
What is the primary function of the viral envelope in enveloped viruses?
What is the primary function of the viral envelope in enveloped viruses?
- To facilitate the degradation of the viral genome
- To protect the virus from the host's immune system
- To provide structural support to the virus
- To interact with the host cell membrane during entry (correct)
Which of the following is a component of the viral capsid in naked viruses?
Which of the following is a component of the viral capsid in naked viruses?
- Viral glycoproteins
- Viral envelope
- Viral enzymes (correct)
- Host-derived lipid bilayer
What is a characteristic of the viral genome in unenveloped viruses?
What is a characteristic of the viral genome in unenveloped viruses?
- It is highly diverse in structure
- It is always segmented
- It is always double-stranded
- It is often circular (correct)
Which of the following viral families has a circular genome?
Which of the following viral families has a circular genome?
What is the primary difference between the structure of enveloped and unenveloped viruses?
What is the primary difference between the structure of enveloped and unenveloped viruses?
Which of the following viruses has a helical capsid and is enveloped?
Which of the following viruses has a helical capsid and is enveloped?
What is the purpose of the spikes formed by viral glycoproteins on the surface of enveloped viruses?
What is the purpose of the spikes formed by viral glycoproteins on the surface of enveloped viruses?
What is the typical size range of viruses, as measured by electron microscopy?
What is the typical size range of viruses, as measured by electron microscopy?
Why are enveloped viruses more fragile than unenveloped viruses?
Why are enveloped viruses more fragile than unenveloped viruses?
What is the primary characteristic that distinguishes enveloped viruses from non-enveloped viruses?
What is the primary characteristic that distinguishes enveloped viruses from non-enveloped viruses?
What is the term for the obligate intracellular parasite that lacks organelles and requires a host cell to replicate?
What is the term for the obligate intracellular parasite that lacks organelles and requires a host cell to replicate?
Which of the following is a characteristic of unenveloped viruses?
Which of the following is a characteristic of unenveloped viruses?
Match the following units
Match the following units
Most viruses with DNA genome is double stranded
Most viruses with DNA genome is double stranded
Icosahedral capsids must be composed of penton capsomers and hexon capsomers.
Icosahedral capsids must be composed of penton capsomers and hexon capsomers.
Penton capsomers have 5 individual proteins
Penton capsomers have 5 individual proteins
Which of the following is not a function of virus capsid proteins?
Which of the following is not a function of virus capsid proteins?
Viral Matrix protein are structural proteins of the virus found in enveloped viruses.
Viral Matrix protein are structural proteins of the virus found in enveloped viruses.
Match the properties of RNA viruses with the correct reasoning
Match the properties of RNA viruses with the correct reasoning
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Study Notes
Virus Structure
- A virus is an obligate intracellular parasite that needs a host cell to replicate, lacks organelles, and is extremely small (filterable agents) ranging from 18-230 nm in size.
Genome Composition
- Viral genomes can be composed of DNA or RNA, and may be single-stranded (ss) or double-stranded (ds).
- Some DNA viruses have circular genomes (e.g., Poxviridae, Asfarviridae, Herpesviridae, Papillomaviridae, Adenoviridae, Papovaviridae).
- Some ds and ss RNA viruses have segmented genomes, which reduces the chances of degradation.
- Parvoviridae and Circoviridae have circular genomes that are mostly double-stranded.
Capsid Structure
- Naked viruses have an icosahedral capsid (e.g., Adenovirus).
- Enveloped viruses have a helical capsid (e.g., Measles virus) or a complex capsid (e.g., Poxvirus).
Properties of Enveloped and Non-Enveloped Viruses
- Enveloped viruses are more pleomorphic (irregularly shaped) and have a viral envelope containing host-derived lipid bilayer and embedded viral glycoproteins.
- Enveloped viruses acquire their envelope by budding through the host cell membrane (except for Poxvirus, which exits by direct fusion).
- Enveloped viruses are more fragile and easily destroyed by detergents, disinfectants, and outside environmental factors.
- Unenveloped viruses are released by lysis of the infected cell and are more environmentally stable.
Biological Properties of Enveloped Viruses
- Enveloped viruses are more easily destroyed by heat, drying, and pH changes.
- Destruction of the envelope destroys the receptors needed for entry, making the virus non-infectious.
- Enveloped viruses are less likely to survive in the gastrointestinal tract.
Biological Properties of Unenveloped Viruses
- Unenveloped viruses are environmentally stable and can survive adverse conditions in the gut.
- They can dry out and retain infectivity, making them more easily spread.
- Unenveloped viruses are more resistant to detergents.
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