Medical Important Viruses
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Questions and Answers

What is a key structural feature for classifying a virus as enveloped or naked?

  • Presence of double-stranded RNA
  • Presence of a lipid-containing membrane (correct)
  • Surface proteins
  • Nucleocapsid shape

Which virus family is classified as a naked icosahedral virus?

  • Papovaviruses (correct)
  • Hepadnaviruses
  • Poxviruses
  • Herpesviruses

What does the presence of virus-specific proteins in an envelope confer?

  • Virus-specific antigenicity (correct)
  • Increased replication speed
  • Stability to the virus
  • Resistance to host immune response

Which of the following viruses is classified as a (-)ssRNA virus?

<p>Rhabdovirus (B)</p> Signup and view all the answers

Which step in the viral replication cycle follows gene expression?

<p>Assembly (C)</p> Signup and view all the answers

What characteristic of enveloped viruses usually affects their appearance?

<p>They appear roughly spherical. (D)</p> Signup and view all the answers

Which of the following viruses is associated with progressive multifocal leukoencephalopathy?

<p>JC virus (D)</p> Signup and view all the answers

What is the diameter of the papovavirus family?

<p>55 nm (D)</p> Signup and view all the answers

What are the two main components that make up a virus?

<p>Genome and capsid (A)</p> Signup and view all the answers

What term is used to describe a complete virus particle?

<p>Virion (D)</p> Signup and view all the answers

Which of the following characteristics is NOT used to classify virus families?

<p>Size of the virion (A)</p> Signup and view all the answers

How does the pathogenicity of a virus vary among closely related species?

<p>It can differ significantly due to structural and functional characteristics. (B)</p> Signup and view all the answers

What is the approximate diameter of the smallest human viruses?

<p>20 nm (D)</p> Signup and view all the answers

What structural feature enhances the ability of some viruses to evade filtration designed to trap bacteria?

<p>Virion size (D)</p> Signup and view all the answers

Which of the following statements is true regarding viral envelopes?

<p>The presence or absence of an envelope distinguishes different virus groups. (A)</p> Signup and view all the answers

What is the term used to describe the capacity of a virus to infect and cause disease in host cells?

<p>Pathogenicity (D)</p> Signup and view all the answers

What forms the basis for the division of viruses into genera and species?

<p>Differences in specific properties like host range and serologic reactions (D)</p> Signup and view all the answers

Which type of RNA virus can be used directly as a template for protein synthesis?

<p>Positive-strand RNA viruses (A)</p> Signup and view all the answers

What is the primary structural feature of helical capsids?

<p>Form a helical cylinder from a single polypeptide species (D)</p> Signup and view all the answers

How are capsomers in icosahedral capsids organized?

<p>Grouped into structural subassemblies (D)</p> Signup and view all the answers

What is a primary characteristic of viruses with double-stranded RNA genomes?

<p>They consist of two complementary RNA strands. (D)</p> Signup and view all the answers

What do the helical and icosahedral configurations of capsids primarily refer to?

<p>The geometric structure of the protein coat surrounding the genome (D)</p> Signup and view all the answers

What type of viral genome is known to be positive polarity?

<p>RNA used as a template for protein synthesis (B)</p> Signup and view all the answers

Which statement accurately describes the nucleocapsid in viral structure?

<p>It consists of protomers and the associated nucleic acid. (A)</p> Signup and view all the answers

What type of DNA do adenoviruses possess?

<p>Double-stranded linear DNA (D)</p> Signup and view all the answers

Which virus family is known for causing latent infections?

<p>Herpesviruses (A)</p> Signup and view all the answers

What is the size and structure of hepadnaviruses?

<p>Double-shelled with an envelope and double-stranded circular DNA (D)</p> Signup and view all the answers

Which of the following viruses is used in the smallpox vaccine?

<p>Vaccinia virus (B)</p> Signup and view all the answers

What type of genetic material do picornaviruses contain?

<p>Single-stranded linear nonsegmented positive-polarity RNA (B)</p> Signup and view all the answers

Which of the following is NOT a pathogen associated with herpesviruses?

<p>Hepatitis B virus (B)</p> Signup and view all the answers

Caliciviruses are characterized by which of the following features?

<p>Naked virus with single-stranded linear positive-polarity RNA (B)</p> Signup and view all the answers

Which family of viruses is associated with causing respiratory tract diseases?

<p>Adenoviruses (C)</p> Signup and view all the answers

What is the primary human pathogen associated with reoviruses?

<p>Rotavirus (C)</p> Signup and view all the answers

Which group of viruses does hepatitis C virus belong to?

<p>Flaviviruses (C)</p> Signup and view all the answers

What characteristic defines retroviruses?

<p>Enveloped with diploid RNA strands (D)</p> Signup and view all the answers

Which pathogen is primarily associated with the alphavirus group?

<p>Eastern and Western encephalitis viruses (C)</p> Signup and view all the answers

What feature distinguishes orthomyxoviruses from other virus families?

<p>Negative-polarity RNA with eight segments (C)</p> Signup and view all the answers

Which of the following viruses is NOT classified under Togaviruses?

<p>Dengue virus (D)</p> Signup and view all the answers

What describes the structure of paramyxoviruses?

<p>Enveloped with helical nucleocapsid (B)</p> Signup and view all the answers

Which virus is known to be associated with mucins due to its affinity?

<p>Influenza virus (C)</p> Signup and view all the answers

Which category of coronavirus vaccines are based on mRNA technology?

<p>Pfizer-BioNTech COVID-19 vaccine (A)</p> Signup and view all the answers

What type of virus is the Johnson & Johnson COVID-19 vaccine based on?

<p>Viral vector (A)</p> Signup and view all the answers

Which viral family includes RNA viruses that do not have an envelope?

<p>Picornaviruses (C)</p> Signup and view all the answers

Which of the following vaccines is based on inactivated virus technology?

<p>Sinovac vaccine (C)</p> Signup and view all the answers

What is the genetic material type of parvoviruses?

<p>Single-stranded DNA (B)</p> Signup and view all the answers

Which of the following statements is true regarding RNA viruses?

<p>Coronaviruses have positive-polarity RNA. (B)</p> Signup and view all the answers

Which vaccine is categorized as a protein-based vaccine?

<p>Novavax vaccine (B)</p> Signup and view all the answers

What defines the classification of viruses primarily?

<p>Nature of the genome and envelope status (A)</p> Signup and view all the answers

Flashcards

Virus

An infectious agent composed of a genome (RNA or DNA) and a protein capsid.

Virion

The complete, infectious particle of a virus, containing the genome and capsid.

Virus Envelope

A protective outer layer of a virus composed of protein and lipids. It helps the virus bind to and enter host cells.

Viral Replication

The process by which a virus uses a host cell's machinery to replicate itself.

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Pathogenicity

The ability of a virus to cause disease in a host organism.

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Virus Family

A group of viruses sharing similar characteristics, such as genome type, replication strategy, capsid structure, and presence or absence of an envelope.

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Virus Genus

A classification category within a virus family, grouping viruses with shared characteristics.

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Virus Species

A specific kind of virus within a genus, sharing unique characteristics.

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What are the basis for classifying viruses into genera and species?

Different characteristics within a virus family, such as host range, serologic reactions, amino acid sequences of viral proteins, and nucleic acid homology, that are used to categorize viruses into genera and species.

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What is a viral genome?

The genetic material of a virus, which can be either RNA or DNA. It can exist in either a single-stranded (ss) or double-stranded (ds) form.

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What are the two types of viral RNA genomes?

Viral RNA genomes can be either positive polarity (messenger RNA sense) or negative polarity (antisense). Positive polarity RNA can be directly translated into proteins, while negative polarity RNA needs to be transcribed into positive polarity first.

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What is a viral capsid?

The protein shell that encloses the viral genome. It can be either helical (rod-shaped or coiled) or icosahedral (spherical or symmetric).

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Describe a viral capsid with helical symmetry.

A capsid with a helical symmetry is made up of repeating units of a single polypeptide species that self-assemble into a helical cylinder. The complex of protomers and nucleic acid is called the nucleocapsid.

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Describe a viral capsid with icosahedral symmetry.

A capsid with an icosahedral symmetry is more complex, consisting of several different polypeptides grouped into structural subassemblies called capsomers. These assemble into an icosahedron, with the nucleic acid genome inside.

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What is a protomer in a helical capsid?

A capsid with helical symmetry is formed by repeating units of a single polypeptide species. These units, called protomers, self-assemble into a helical cylinder.

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What is a nucleocapsid?

The complex formed by protomers and nucleic acid in a helical capsid.

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Naked Virus

A virus that lacks a lipid-containing membrane surrounding its nucleocapsid.

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Viral Replication Cycle

The process by which a virus replicates within a host cell, involving attachment, penetration, uncoating, gene expression, replication, assembly, and release of new viral progeny.

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Baltimore Classification

A system for classifying viruses based on the structure and properties of their genomes.

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Group I Viruses

A group of viruses in the Baltimore classification that have double-stranded DNA as their genetic material.

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Papovaviruses

A family of viruses characterized by naked, icosahedral capsids and double-stranded circular DNA.

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What are Adenoviruses?

Naked icosahedral viruses with a double-stranded linear DNA genome. They cause pharyngitis, respiratory infections, and other less common infections.

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What are Hepadnaviruses?

Double-shelled viruses with an icosahedral capsid and a double-stranded circular DNA genome. They cause hepatitis B.

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What are Herpesviruses?

Enveloped viruses with an icosahedral nucleocapsid and a double-stranded linear DNA genome. They cause latent infections and are known for their ability to stay dormant in the body.

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What are Poxviruses?

The largest viruses with a brick-like shape, an envelope, and a complex capsid symmetry. They cause skin lesions called 'pocks'.

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What are RNA Viruses?

A group of viruses that encompass both naked icosahedral and enveloped viruses. They have RNA as their genetic material.

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What are Picornaviruses?

Small RNA viruses with a naked icosahedral capsid and a single-stranded, linear, positive-polarity RNA genome. They cause a variety of infections, including polio, the common cold, and hepatitis A.

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What are Caliciviruses?

Naked viruses with an icosahedral capsid and a single-stranded, linear, positive-polarity RNA genome. They cause a variety of gastroenteritis infections.

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What are Enveloped Helical RNA Viruses?

Enveloped viruses with a helical capsid and a single-stranded linear RNA genome. They are responsible for a variety of human infections, including influenza, rabies, and Ebola.

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Reoviruses

A group of viruses that are characterized by their naked structure, icosahedral capsid coats, and 10 segments of double-stranded linear RNA.

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Rotavirus

A major human pathogen belonging to the Reovirus family that causes diarrhea primarily in infants.

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Flaviviruses

These viruses are enveloped with an icosahedral capsid and have a single-stranded, linear, nonsegmented, positive-polarity RNA genome.

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Rubivirus

An enveloped virus with an icosahedral capsid and a single-stranded, linear, nonsegmented, positive-polarity RNA genome, specifically known to cause rubella.

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Retroviruses

An enveloped virus with an icosahedral capsid and two identical strands of single-stranded, linear, positive-polarity RNA. They are known for their unique reverse transcription process.

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Oncoviruses

A group of retroviruses that are known to cause cancer, such as human T-cell leukemia virus (HTLV).

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Lentiviruses

A group of retroviruses that are known to cause slow and persistent infections, such as human immunodeficiency virus (HIV).

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Orthomyxoviruses

These viruses are enveloped with a helical nucleocapsid and eight segments of linear, single-stranded, negative-polarity RNA. They have an affinity for mucins.

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How are viruses classified?

Viruses are classified based on their genetic material (DNA or RNA), presence or absence of an envelope, and other structural features.

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What is a viral envelope?

An envelope is a protective outer layer made of lipids and proteins that surrounds some viruses. It helps the virus bind to and enter host cells.

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What are naked nucleocapsid viruses?

Naked nucleocapsid viruses lack an envelope and consist only of a protein capsid surrounding the genetic material.

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What are viruses with segmented RNA?

Viruses with segmented RNA have their genetic information divided into multiple smaller segments. Influenza viruses are an example.

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What are viruses with single-stranded RNA?

Viruses with single-stranded RNA have their genetic information in a single uninterrupted strand. Examples include picornaviruses and coronaviruses.

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What are viruses with positive-polarity RNA?

Viruses with positive-polarity RNA have a genome that can be directly translated into proteins. Examples include coronaviruses.

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Study Notes

Medical Important Viruses

  • Viruses are infectious agents, minimally constructed of a genome (RNA or DNA, but not both) and a protein-containing structure (capsid).
  • Some viruses have additional features like an envelope (lipid bilayer).
  • A complete virus particle is called a virion.
  • Viruses replicate inside host cells.
  • Viral pathogenicity depends on structural and functional characteristics.
  • Different viruses within a family may have different clinical pathologies.
  • Viruses are significantly smaller than cells (100-1000x smaller).
  • Viruses pass through filters designed to trap bacteria.
  • Viruses are classified into families, genera, and species based on characteristics like viral nucleic acid type, replication strategy, capsid symmetry, and presence of an envelope.
  • Viruses have a protein shell (capsid) that encloses the genome, either helical or icosahedral in structure.
  • The capsid is constructed of multiple copies of a single or several polypeptides.
  • The nucleocapsid is the complex of protomers and nucleic acid.
  • Some viruses have an envelope, derived from host cell membranes, which is important for classifying viral families.
  • The envelope is composed of a lipid bilayer with viral proteins.
  • Viruses have various single- or double-stranded genomes, often RNA.
  • Positively-polarity RNA can be directly used as a protein synthesis template.
  • Negatively-polarity RNA requires complementary mRNA for protein synthesis.
  • Viral replication involves attachment, penetration, uncoating, gene expression, replication, assembly, and progeny release.

Viral Classification

  • Viruses are classified based on their genome type (DNA or RNA), strandedness, and symmetry.
  • Baltimore classification system categorizes viruses into seven groups based on their genome and mechanism of mRNA production.
  • Example groups include dsDNA, ssDNA, dsRNA, (+)ssRNA, (-)ssRNA, (+)ssRNA-RT, and dsDNA-RT.

Summary of Important Virus Families

  • DNA Viruses: Naked icosahedral viruses (parvoviruses, papovaviruses, adenoviruses); enveloped icosahedral viruses (herpesviruses, hepadnaviruses); poxviruses (complex internal symmetry).
  • RNA Viruses: Naked icosahedral viruses (picornaviruses, caliciviruses, reoviruses); enveloped helical viruses (influenza, mumps, measles, parainfluenza, respiratory syncytial viruses), enveloped icosahedral viruses (togoviruses, flaviviruses); retroviruses, bullet-shaped viruses (filoviruses) with helical nucleocapsid, single stranded linear non-segmented RNA, nonsegmented RNA

Specific Virus Examples (with examples of diseases they cause)

  • Adenoviruses: Mild respiratory infections, some cancers.
  • Papovaviruses: Progressive multifocal leukoencephalopathy, some cancers.
  • Herpesviruses: Herpes simplex, varicella-zoster, cytomegalovirus, Epstein-Barr virus (various infections).
  • Hepadnaviruses: Hepatitis B
  • Poxviruses: Smallpox, monkeypox (various skin lesions)
  • Picornaviruses: Polio, common cold, hepatitis A (various diseases)
  • Caliciviruses: Norovirus (gastroenteritis).
  • Reoviruses: Rotavirus (diarrhea).
  • Togaviruses: Rubella virus (German measles), several encephalitis viruses.
  • Flaviviruses: Yellow fever, dengue, West Nile encephalitis (various diseases).
  • Retroviruses: HIV (AIDS) human T cell leukemia viruses.
  • Orthomyxoviruses: Influenza viruses
  • Paramyxoviruses: Measles, mumps, parainfluenza, respiratory syncytial viruses (respiratory infections).
  • Rhabdoviruses: Rabies
  • Filoviruses: Ebola virus, Marburg virus (severe hemorrhagic fever).
  • Coronaviruses: Common colds, SARS, MERS, COVID-19 (severe respiratory infections)

Additional notes

  • Coronavirus disease 2019 (COVID-19) is caused by the SARS-CoV-2 SARS Virus.
  • Various molecular diagnostic tests (nucleic acid detection, serology) are used to identify and diagnose active or recent infections with some viruses.
  • Different types of COVID-19 vaccines are now widely available including mRNA based vaccines (Pfizer, Moderna), inactivated virus vaccines (Sinovac, Sinopharm), and viral vector vaccines (Oxford/AstraZeneca, Sputnik).
  • Unvaccinated individuals are 17 times more likely to be hospitalized with Covid-19.
  • COVID-19 vaccines are effective against infection and severe illness from related viruses.

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Description

This quiz explores the fundamental concepts of important viruses, including their structure, replication, and classification. Understand the key differences in viral families, their pathogenicity, and the characteristics that define various viruses. Perfect for students studying virology or infectious diseases.

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