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Questions and Answers
What is the name for the complete, infective form of a virus outside of a host cell?
What is the name for the complete, infective form of a virus outside of a host cell?
Virion
What are the two types of nucleic acid a viral genome can contain?
What are the two types of nucleic acid a viral genome can contain?
RNA or DNA
Viruses can synthesize their own proteins.
Viruses can synthesize their own proteins.
False
What is the function of the protein coat surrounding the nucleic acid genome of a virus?
What is the function of the protein coat surrounding the nucleic acid genome of a virus?
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Match the following viral families with their respective nucleic acid types.
Match the following viral families with their respective nucleic acid types.
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Which of these is NOT a characteristic of enveloped viruses?
Which of these is NOT a characteristic of enveloped viruses?
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Which of the following is a major site of viral disease?
Which of the following is a major site of viral disease?
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The ability of a virus to infect a particular cell, tissue, or host species is known as ______.
The ability of a virus to infect a particular cell, tissue, or host species is known as ______.
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What is the name of the protein that allows the Influenza A virus to attach to host cells?
What is the name of the protein that allows the Influenza A virus to attach to host cells?
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What are the six steps involved in the viral replication cycle?
What are the six steps involved in the viral replication cycle?
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What are the two types of viral infection based on the presence or absence of symptoms?
What are the two types of viral infection based on the presence or absence of symptoms?
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What are the four types of symptomatic viral infections?
What are the four types of symptomatic viral infections?
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DNA viruses typically replicate in the cytoplasm of the host cell.
DNA viruses typically replicate in the cytoplasm of the host cell.
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What is the name of the enzyme used by viruses that have their own polymerases?
What is the name of the enzyme used by viruses that have their own polymerases?
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Which family of viruses has their enzymes located in their nucleocapsids?
Which family of viruses has their enzymes located in their nucleocapsids?
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The (+) sense RNA viral genome can directly act as mRNA.
The (+) sense RNA viral genome can directly act as mRNA.
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The (-) sense RNA viral genome can directly act as mRNA.
The (-) sense RNA viral genome can directly act as mRNA.
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Influenza viruses replicate their (-) sense RNA in the nucleus.
Influenza viruses replicate their (-) sense RNA in the nucleus.
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Which of these viruses are considered (+) sense RNA viruses?
Which of these viruses are considered (+) sense RNA viruses?
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Which of these viruses are considered (-) sense RNA viruses?
Which of these viruses are considered (-) sense RNA viruses?
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The HIV virus genome is segmented.
The HIV virus genome is segmented.
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The Paramyxoviridae family of viruses is segmented.
The Paramyxoviridae family of viruses is segmented.
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Which of these is NOT a type of viral capsid symmetry?
Which of these is NOT a type of viral capsid symmetry?
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What are the three main types of viral capsid symmetry?
What are the three main types of viral capsid symmetry?
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Which of the following is not a step in the viral replication cycle?
Which of the following is not a step in the viral replication cycle?
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What is the name of the protein that plays a crucial role in viral attachment and is commonly targeted by antiviral drugs?
What is the name of the protein that plays a crucial role in viral attachment and is commonly targeted by antiviral drugs?
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Give the name of three viruses that use the following viral attachment proteins to attach to host cells:
a) Rhinovirus:
b) Adenovirus:
c) Rotavirus:
Give the name of three viruses that use the following viral attachment proteins to attach to host cells:
a) Rhinovirus: b) Adenovirus: c) Rotavirus:
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Viral tropism only refers to the ability of a virus to infect a specific species.
Viral tropism only refers to the ability of a virus to infect a specific species.
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Viral replication occurs independently of the host cell.
Viral replication occurs independently of the host cell.
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What are the two major factors that influence the intensity of viral infection and the resulting symptoms?
What are the two major factors that influence the intensity of viral infection and the resulting symptoms?
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Study Notes
Viruses
- Smallest infectious agents (18-600 nm)
- Filterable agents
- Cannot be seen by ordinary microscopes
- Rhinovirus 30nm
- HIV 120nm
- T4 bacteriophage 200nm
- Hepatitis B 42nm across
- Mimivirus 500-700nm across
- Mycoplasma pneumoniae 100nm wide, 1,000nm long
- E. coli bacterium 2,000nm long
- Human red blood cell 8,000nm diameter
Viral Characteristics
- Cannot synthesize their own proteins, so cannot form their own energy
- Obligate intracellular parasite (needs a host)
- Non-living infectious agents
- Viral genome can be RNA or DNA (but not both)
Virus Taxonomy
- Classification by ICTV (International Committee on Taxonomy of Viruses)
- Order – virales (suffix)
- Family – viridae
- Subfamily – virinae
- Genus – virus
- Species - (trivial name preserved)
Virus Nomenclature
- Structure: size, morphology, and nucleic acid (e.g., picornavirus (small RNA), togavirus)
- Biochemical characteristics: structure and mode of replication
- Disease: encephalitis and hepatitis viruses (examples)
- Means of transmission: arbovirus spread by insects (example)
- Host cell (host range): animal (human, mouse, bird), plant, bacteria
- Tissue or organ (tropism): adenovirus and enterovirus
Virus Structure
-
Virion: the complete, infective form of a virus outside a host cell
-
Enveloped virus
- Envelope protein
- Envelope
- Viral genome
- Nucleocapsid
- Viral tegument
-
Naked virus
- Nucleocapsid
- Viral genome
- Capsomeres
-
Nucleic acid genome (single- or double-stranded RNA or DNA)
-
Protein coat (capsid) made up of capsomeres
-
Nucleocapsid: the nucleic acid genome plus the protective protein coat
-
Envelope: viruses obtain their envelope by budding through a host cell membrane. (internal cell membranes like those of the Golgi body or the nucleus. Composed of lipids, protein and glycoproteins (may/may not have))
-
Viral attachment protein (VAP): surface structures of the envelope and the capsid
Virus Classification
- A. Viral structure: Naked or enveloped?
- B. Genome structure: DNA or RNA, Single-stranded or double-stranded, Segmented or non-segmented
- C. Capsid Symmetry: Icosahedral/cubic/spherical, Helical/pleomorphic, Complex
Naked Viruses
- Resistant to environmental conditions (heat, acid, proteases, detergents, dryness)
- Easily transmitted (object and surfaces, hand-to-hand transmission)
- Many can be transmitted via fecal-oral route
Enveloped Viruses
- Cannot withstand conditions that naked viruses are resistant to; are fragile
- Usually labile to treatment with acid and detergents
- Precludes transmission by the fecal-oral route
- Must remain wet and spread via respiratory droplets, blood, mucus, saliva and semen; by injection or organ transplants
Viral Genome
- DNA or RNA, single or double-stranded
- Segmented or non-segmented
RNA Viruses
- dsRNA (double-stranded RNA)
- ssRNA (single-stranded RNA)
- (+) sense: can directly act as mRNA, binds to ribosomes, used directly in protein synthesis, sufficient to start infection
- (-) sense: are not sufficient. A polymerase must be carried into the cell with the genome; A full-length (+) strand RNA must be produced by the viral polymerase to act as a template
- ssRNA (RT): single-stranded RNA (reverse transcriptase)
Medically Important Viruses
- Specific examples of DNA and RNA viruses mentioned in the slides
Viral Replication Steps
- Detection of the target cell
- Attachment
- Penetration
- Uncoating
- Macromolecule synthesis
- Viral assembly
- Release
- Budding (for enveloped viruses)
Viral Attachment Proteins
- Specific proteins for different viruses, playing a role in infection
- Examples for several viruses
Major Sites of Viral Disease
- Respiratory system
- Gastrointestinal system
- Skin, mouth, and genital (epithelial) mucosal sites
- Lymphoid tissues
- Liver
- Central Nervous System
Viral Infection Types
- Asymptomatic (subclinical) infections
- Latent infections
- Symptomatic infections
- Acute
- Subacute
- Chronic
- Persistent
Viral Diseases
- Intensity depends on host-related factors and viral factors
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Description
This quiz covers essential aspects of viruses, including their characteristics, classification, and nomenclature. You will learn about different types of viruses, their sizes, and their vital roles as obligate intracellular parasites. Test your knowledge on the taxonomy of viruses according to the ICTV guidelines.
