19 Questions
What is the primary function of the viral envelope in enveloped viruses?
To interact with the host cell membrane during entry
Which of the following is a component of the viral capsid in naked viruses?
Viral enzymes
What is a characteristic of the viral genome in unenveloped viruses?
It is often circular
Which of the following viral families has a circular genome?
Papovaviridae
What is the primary difference between the structure of enveloped and unenveloped viruses?
The presence or absence of a viral envelope
Which of the following viruses has a helical capsid and is enveloped?
Rhabdoviridae
What is the purpose of the spikes formed by viral glycoproteins on the surface of enveloped viruses?
To interact with the host cell membrane during entry
What is the typical size range of viruses, as measured by electron microscopy?
18-230 nm
Why are enveloped viruses more fragile than unenveloped viruses?
Because their envelope is susceptible to environmental stresses
What is the primary characteristic that distinguishes enveloped viruses from non-enveloped viruses?
Presence of a lipid bilayer membrane
What is the term for the obligate intracellular parasite that lacks organelles and requires a host cell to replicate?
Virus
Which of the following is a characteristic of unenveloped viruses?
Environmentally stable
Match the following units
1mm = 10^(-3) cm 1 um = 10^(-6) cm 1nm = 10^(-9)cm 10nm = 10^(-8) cm
Most viruses with DNA genome is double stranded
True
Icosahedral capsids must be composed of penton capsomers and hexon capsomers.
False
Penton capsomers have 5 individual proteins
True
Which of the following is not a function of virus capsid proteins?
Replicate viral genome
Viral Matrix protein are structural proteins of the virus found in enveloped viruses.
False
Match the properties of RNA viruses with the correct reasoning
Some can reassort or swap genes = because they are segmented variable = replicated using RNA polymerase which is error prone as it had no proof reading mechanism adapt easily to new environments = can evolve rapidly if needed often zoonotic = variable and new genes can be introduced
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.
Test your knowledge on the structure of viruses, including naked and enveloped viruses, viral nucleic acid, capsid, viral enzymes, and lipid bilayer. Learn about the key components of viruses and how they interact with each other. This quiz covers the basics of virus structure and its importance in virology.
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