Questions and Answers
What type of symmetry do most viruses possess when they have an elongated shape?
Which virus is an example of one with a complex capsid structure?
Which function is NOT typically associated with the viral capsid?
What characteristic defines an icosahedral virus structure?
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Which type of capsid is described as having rod-shaped capsomers that coil around a hollow center?
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What is the primary function of the viral capsid?
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Which statement accurately describes the virion?
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How are viruses classified into families?
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What does the suffix '-viridae' indicate in virus naming?
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Which component of a virus is not always present?
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Which of the following is a reason for how viruses are named?
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What is a nucleocapsid?
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What constitutes the basic building blocks of a viral coat?
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What defines viruses as obligate intracellular parasites?
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Which component is found in viruses but not in bacteria or other cells?
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Which of the following statements about viruses is true?
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How does the genetic material of a virus typically function upon entering a host cell?
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What is a defining characteristic of a defective virus?
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What distinguishes enveloped viruses from non-enveloped viruses?
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What size range do most viruses fall into?
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Which of the following properties is NOT characteristic of viruses?
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What is the defining feature of an icosahedral virus?
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Which virus is categorized as an enveloped icosahedral virus?
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What distinguishes complex viruses from other types of viruses?
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Which of the following viruses is NOT classified as an icosahedral virus?
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What type of genetic material can a bacteriophage carry?
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Which of the following viruses has a helical symmetry?
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Which statement best describes capsomers?
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Which virus is known to lack a normal capsid?
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Study Notes
General Properties of Viruses
- Viruses are the smallest infectious agents, capable of infecting animals, plants, and bacteria.
- Obligate intracellular parasites; they require living host cells for replication.
- Inert life forms, consisting of nucleoprotein and are filterable.
- Size ranges from 10 nm to 300 nm, significantly smaller than other microorganisms.
- Viral genome can be either DNA or RNA, protected by a protein coat and sometimes a lipid membrane.
- Viruses lack metabolic activity outside host cells, do not have ribosomes, and rely on host cellular machinery for replication.
Virus vs. Cells
- Viruses contain either DNA or RNA, while cells contain both.
- Viruses have a limited number of proteins; cells have many.
- Lipoprotein membranes are present in some viruses; all cells have a cell membrane.
- Viruses lack ribosomes and mitochondria, while cells contain both.
- Viruses do not replicate by binary fission, unlike most cells which do.
Terms & Definitions in Virology
- Capsid: Protein shell enclosing the viral genome.
- Capsomeres: Units forming the capsid, visible in electron microscopy.
- Defective Virus: Replication-deficient virus particle.
- Envelope: Lipid membrane that surrounds some viruses, obtained through cellular budding.
- Nucleocapsid: Combined structure of the protein coat and nucleic acid.
- Virion: Complete virus particle, containing the nucleocapsid and possibly an envelope.
Viral Structure
- Basic virus structure includes a core of nucleic acid within a protein coat, protecting the genome from environmental factors.
- Three types of capsid symmetry:
- Cubic: Icosahedral structure with 20 equilateral triangular faces; e.g. adenovirus.
- Helical: Protein coils around RNA or DNA forming a spiral; e.g. coronaviruses.
- Complex: Viruses that do not conform to either symmetry; e.g. poxvirus.
Function of Virion Structure
- Protects genetic material during transmission.
- Assists in viral entry into host cells.
- Packages enzymes needed for early infection stages.
Capsid Morphological Types
- Helical Capsid: Rod-shaped capsomers that coil around nucleic acid; examples include influenza and rabies viruses.
- Icosahedral Capsid: 20-sided with 12 corners; varies in capsomer number and composition, includes enveloped variants.
Classification of Viruses
- Viruses are classified based on structural properties, size, nucleic acid type, host species, and target cells.
- Family names end in -viridae, subfamily in -virinae, and genus in -virus.
- Example: Herpesviridae family includes Herpes Simplex Virus (HSV-I), known for causing cold sores.
Naming of Viruses
- Names derived from diseases caused (e.g., poliovirus), types of diseases (e.g., murine leukemia virus), geographic locations (e.g., Sendai virus), and discoverers (e.g., Epstein-Barr virus).
Complex Viruses
- Possess additional structures that deviate from typical capsid forms.
- Example includes poxviruses, which lack a traditional capsid and have layers of lipoproteins.
Bacteriophages
- Specific viruses that infect bacteria by injecting genetic material through an outer protein capsid.
- Can contain ssRNA, dsRNA, ssDNA, or dsDNA, and feature a polyhedral head, helical tail, and attachment fibers.
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Description
Explore the fundamental characteristics that define viruses as the smallest infectious agents. This quiz delves into their unique properties, including their nature as obligate intracellular parasites and their interactions with various forms of life. Test your knowledge of medical virology and the distinctions between viruses and other microorganisms.
