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Questions and Answers
What is the term for a virus that lacks a lipid-containing membrane?
What is the term for a virus that lacks a lipid-containing membrane?
How does the structure of the nucleocapsid in enveloped viruses typically appear?
How does the structure of the nucleocapsid in enveloped viruses typically appear?
Which classification group includes enveloped viruses with double-stranded circular DNA?
Which classification group includes enveloped viruses with double-stranded circular DNA?
What type of viral genome do adenoviruses possess?
What type of viral genome do adenoviruses possess?
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Which of the following viruses is classified under Group IV?
Which of the following viruses is classified under Group IV?
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What characteristic distinguishes the papovaviruses from other virus families?
What characteristic distinguishes the papovaviruses from other virus families?
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Which of the following viruses is NOT considered a naked virus?
Which of the following viruses is NOT considered a naked virus?
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Which group of viruses does NOT include any enveloped viruses?
Which group of viruses does NOT include any enveloped viruses?
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What is the main human pathogen associated with reoviruses?
What is the main human pathogen associated with reoviruses?
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Which virus is categorized under flaviviruses?
Which virus is categorized under flaviviruses?
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What characteristic is true for retroviruses?
What characteristic is true for retroviruses?
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What distinguishes orthomyxoviruses from paramyxoviruses?
What distinguishes orthomyxoviruses from paramyxoviruses?
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Which group of viruses includes the rubella virus?
Which group of viruses includes the rubella virus?
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Which of the following statements about hepatovirus is correct?
Which of the following statements about hepatovirus is correct?
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Which virus is not associated with causing human disease?
Which virus is not associated with causing human disease?
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What two components constitute a virus?
What two components constitute a virus?
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Which virus is classified as a lentivirus?
Which virus is classified as a lentivirus?
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What is the purpose of the capsid in a virus?
What is the purpose of the capsid in a virus?
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Which of the following statements defines a complete virus particle?
Which of the following statements defines a complete virus particle?
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What are the smallest known viruses called?
What are the smallest known viruses called?
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Which structural feature is not always present in viruses?
Which structural feature is not always present in viruses?
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What type of genetic material do adenoviruses possess?
What type of genetic material do adenoviruses possess?
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What characteristics are used to categorize viruses into families?
What characteristics are used to categorize viruses into families?
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Which of the following viruses are known to cause latent infections?
Which of the following viruses are known to cause latent infections?
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How do the sizes of viruses compare to the cells they infect?
How do the sizes of viruses compare to the cells they infect?
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Which of the following is least likely to be a characteristic for defining virus families?
Which of the following is least likely to be a characteristic for defining virus families?
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What is a distinctive feature of hepadnaviruses compared to other virus families?
What is a distinctive feature of hepadnaviruses compared to other virus families?
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Which of the following is true about poxviruses?
Which of the following is true about poxviruses?
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What type of RNA do picornaviruses contain?
What type of RNA do picornaviruses contain?
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Which family of viruses causes infections related to upper and lower respiratory tracts?
Which family of viruses causes infections related to upper and lower respiratory tracts?
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Which virus is specifically mentioned as used in the smallpox vaccine?
Which virus is specifically mentioned as used in the smallpox vaccine?
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What feature is common to all families of RNA viruses mentioned?
What feature is common to all families of RNA viruses mentioned?
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What is the primary mode of transmission for MERS to humans?
What is the primary mode of transmission for MERS to humans?
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What virus strain is responsible for COVID-19?
What virus strain is responsible for COVID-19?
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What is the only important human pathogen among Rhabdoviruses?
What is the only important human pathogen among Rhabdoviruses?
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What percentage of people recover from COVID-19 without special treatment?
What percentage of people recover from COVID-19 without special treatment?
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Which viruses are responsible for causes of severe pneumonia that emerged in 2002 and 2012?
Which viruses are responsible for causes of severe pneumonia that emerged in 2002 and 2012?
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What is the polarity of the RNA found in coronaviruses?
What is the polarity of the RNA found in coronaviruses?
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Which of the following symptoms is NOT commonly associated with COVID-19?
Which of the following symptoms is NOT commonly associated with COVID-19?
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What is a common feature of Filoviruses?
What is a common feature of Filoviruses?
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What is the incubation period for COVID-19 in general?
What is the incubation period for COVID-19 in general?
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Who is more likely to develop serious illness from COVID-19?
Who is more likely to develop serious illness from COVID-19?
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Which outbreak was associated with a high fatality rate of approximately 9%?
Which outbreak was associated with a high fatality rate of approximately 9%?
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On what date did WHO declare COVID-19 as a pandemic?
On what date did WHO declare COVID-19 as a pandemic?
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What animal is considered the natural reservoir for CoV-SARS?
What animal is considered the natural reservoir for CoV-SARS?
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Which of the following statements about MERS-CoV is true?
Which of the following statements about MERS-CoV is true?
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What is the primary cause of the common cold among human viruses?
What is the primary cause of the common cold among human viruses?
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What distinguishes the shape of Rhabdoviruses from other virus families?
What distinguishes the shape of Rhabdoviruses from other virus families?
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Study Notes
Medical Important Viruses
- Viruses are infectious agents, minimally constructed of a genome (RNA or DNA, not both) and a protein-containing structure (capsid).
- Many viruses have additional features, like an envelope, a protein-containing lipid bilayer. This distinguishes different virus groups.
- A complete virus particle is called a virion.
- Viruses only produce in host cells.
- A virion can be viewed as a delivery system to surround a nucleic acid payload.
- The virus payload is the viral genome and may also contain enzymes needed for viral replication, a process that is intracellular.
Virus Structure
- Viruses are much smaller than cells (100-1000 times smaller).
- The smallest viruses have a diameter of 20 nm, while the largest are about 300 nm.
- They often pass through filters used to catch bacteria.
Viral Classification
- Viruses are categorized into families, subfamilies, genera, and species.
- Factors used in classification include: type and structure of nucleic acid, replication strategy, capsid symmetry (helical or icosahedral), and presence/absence of an envelope.
Viral Genome
- Viral genomes can be either DNA or RNA, and single-stranded or double-stranded.
- Common viral genomes are often single-stranded RNA.
- Single-stranded RNA is further subdivided into positive-polarity (mRNA sense) and negative-polarity (antisense). Positive polarity can directly be used as a template for protein synthesis.
Capsid Symmetry
- The capsid, the protein shell enclosing the genome, has either a helical or icosahedral symmetry.
- Helical symmetry is rod-shaped, while icosahedral is spherical.
- These structures are composed of multiple copies of one or more polypeptides.
Envelopes
- Many viruses have a lipid-containing membrane surrounding the nucleocapsid, which is called the envelope (a significant way to categorize viruses).
- Viruses lacking an envelope are called naked viruses.
- Envelopes are derived from the host cell's membranes and contain virus-specific proteins.
Viral Replication
- Viral replication follows steps including attachment to host cells, penetration, uncoating, gene expression, replication, assembly, and release.
- Gene expression and replication are followed by progeny virion assembly and release.
Viral Classification (Baltimore)
- Viruses are grouped into 7 categories based on their genome's structure and strategy. These are based on the nature of the nucleic acid and their strategies of replication.
DNA Viruses
- Three naked, icosahedral groups - parvoviruses, papovaviruses, adenoviruses – are categorized by size, with increasing particle size.
- Hepadnaviruses and herpesviruses are enveloped, icosahedral.
- Poxviruses have a complex internal symmetry, being among the largest.
Papovaviruses
- These are naked, icosahedral viruses with double-stranded circular supercoiled DNA.
- They include papilloma, polyoma, and simian vacuolating viruses (SV40).
- There are clinical significances of this group.
Adenoviruses
- Naked, icosahedral viruses with double-stranded linear DNA.
- They cause pharyngitis, respiratory disease, and cause sarcomas in animals.
Hepadnaviruses
- These are enveloped viruses with icosahedral nucleocapsids, a double-stranded DNA, which is unusual since its other strand is missing ~25% of its length.
- Hepatitis B is the human pathogen associated with this family.
Herpesviruses
- These are enveloped viruses with an icosahedral nucleocapsid and double-stranded DNA; the envelope has a unique shape.
- They include herpes simplex virus types 1 and 2, varicella-zoster virus, cytomegalovirus, and Epstein-Barr virus.
Poxviruses
- Large, brick-shaped enveloped viruses with complex symmetry composed of double-stranded DNA.
- Some causes of skin pox include smallpox (vaccinia virus is used for vaccine)
RNA Viruses (General)
- Reoviruses, a group of RNA viruses, have a double-stranded RNA genome.
- Many other RNA virus families share single-stranded RNA as their genome, with some linear, some circular in arrangement.
Picornaviruses
- Smallest of the RNA viruses with a single-stranded, positive-polarity RNA, non-segmented genome.
- Naked, icosahedral capsid.
- Major human pathogens are enteroviruses (polio) and rhinoviruses (common cold).
Caliciviruses
- Naked, icosahedral RNA viruses with single-stranded, positive-polarity RNA.
- Cause diarrhea among various human lineages (Norwalk virus).
Reoviruses
- RNA viruses, have a double-stranded RNA genome with 10 segments, linear.
- Respiratory enteric orphan virus, primarily causes diarrhea (Rotavirus)
Flaviviruses
- Enveloped, icosahedral RNA Viruses with single-stranded positive-polarity RNA, causing yellow fever, dengue virus, West Nile virus, and Japanese encephalitis.
- The family is highly diverse, with clinical significance.
Togaviruses
- Enveloped, icosahedral RNA Viruses with single-stranded positive-polarity RNA, causing eastern and western encephalitis diseases and rubella.
Retroviruses
- Enveloped, icosahedral RNA Viruses with a single-stranded positive-polarity RNA, with a reverse transcription mechanism.
- Human immunodeficiency virus (HIV) is the most significant pathogen.
Orthomyxoviruses
- Enveloped, helical RNA viruses with negative-polarity RNA in eight segments.
- Primarily cause flu (influenza virus), significant pathogen in human health.
Paramyxoviruses
- Enveloped, helical RNA viruses with negative-polarity RNA, nonsegmented.
- Measles, mumps, parainfluenza, and respiratory syncytial viruses are the most important pathogens in this group, with significances in human health.
Rhabdoviruses
- Enveloped, bullet-shaped viruses with helical nucleocapsid, single-stranded, linear, non-segmented, negative-polarity RNA.
- Rabies virus is only significant pathogen in this viral family.
Filoviruses
- Enveloped RNA viruses with helical nucleocapsid and single-stranded, linear, nonsegmented, negative-polarity RNA.
- Very severe pathogens include Ebola virus and Marburg virus, with significances in human health.
Coronaviruses
- Enveloped, helical RNA viruses with single-stranded, linear, nonsegmented, positive-polarity RNA.
- Respiratory tract infections like the common cold and SARS, MERS, and COVID-19 highlight their importance for human health.
Viral Diseases
- Viruses cause numerous diseases categorized based on symptoms and tissue or organ systems affected.
Molecular Tests and COVID-19
- Molecular tests detect the presence of viral RNA.
- Antibody tests detect presence of antibodies in the patient. Both can aid in diagnosis of the COVID-19 infection.
Viral Vaccines
- Various COVID-19 vaccines are available. including mRNA vaccines, inactivated virus vaccines, viral vector vaccines, and protein based.
COVID-19 Variants
- Several versions of the SARS-CoV-2 virus have been identified, and these mutations/evolution are significant.
Summary of virus classification
- Viruses are primarily categorized by their genome (DNA or RNA) and their presence/absence of an envelope.
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Description
This quiz covers essential information about viruses, including their structure, classification, and replication processes. It highlights the differences between various virus groups and the role of a virion as a delivery system for viral genome and enzymes. Test your knowledge on the fundamentals of virology!
