Chapter 15: DNA/RNA Viruses Classification

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Questions and Answers

What are the two groups of DNA?

dsDNA or ssDNA

Is dsDNA enveloped or nonenveloped?

  • Nonenveloped
  • Can be either (correct)
  • Neither
  • Enveloped

Is ssDNA enveloped or nonenveloped?

  • Nonenveloped (correct)
  • Enveloped
  • Neither
  • Can be either

What virus families are found in nonenveloped dsDNA?

<p>Adenoviridae and Papillomaviridae</p> Signup and view all the answers

What virus families are found in enveloped dsDNA?

<p>Poxviridae, Herpesviridae, and Hepadnaviridae</p> Signup and view all the answers

What virus families are found in nonenveloped ssDNA?

<p>Parvoviridae</p> Signup and view all the answers

What are the two groups of RNA?

<p>ssRNA or dsRNA</p> Signup and view all the answers

Is ssRNA positive sense or negative sense?

<p>Can be either (B)</p> Signup and view all the answers

Is positive sense ssRNA, nonenveloped or enveloped?

<p>Can be either (D)</p> Signup and view all the answers

What is the meaning of positive sense ssRNA viruses?

<p>They act as mRNA.</p> Signup and view all the answers

What virus families are in positive sense, nonenveloped, ssRNA?

<p>Picornaviridae and Caliciviridae</p> Signup and view all the answers

What virus families are in positive sense, enveloped, ssRNA?

<p>Coronaviridae, Retroviridae, Flaviviridae, and Togaviridae</p> Signup and view all the answers

What is the meaning of negative sense ssRNA?

<p>They are complementary base to the mRNA.</p> Signup and view all the answers

Are negative sense ssRNA, enveloped or nonenveloped?

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

What virus families are found in negative sense, enveloped, ssRNA?

<p>Filoviridae, Orthomyxoviridae, Paramyxoviridae, Arenaviridae, and Bunyaviridae</p> Signup and view all the answers

Is dsRNA positive sense or negative sense?

<p>Neither (D)</p> Signup and view all the answers

Is dsRNA enveloped or nonenveloped?

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

What virus family is found in nonenveloped dsRNA?

<p>Reoviridae</p> Signup and view all the answers

Which is smaller, the genome of RNA viruses or the genome of DNA viruses?

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

What does the genome of RNA heavily depend on?

<p>Host cell's proteins and enzymes for replication</p> Signup and view all the answers

Why is the genome of RNA more prone to errors (mutations)?

<p>RNA polymerase lacks proofreading ability.</p> Signup and view all the answers

What are retroviruses?

<p>Viruses that replicate indirectly through a DNA intermediate.</p> Signup and view all the answers

What are DNA viruses?

<p>Viruses that replicate in the host cell.</p> Signup and view all the answers

What are RNA viruses?

<p>Viruses that replicate in the host cell ribosomes.</p> Signup and view all the answers

Flashcards

DNA Virus Categories

Double-stranded (dsDNA) or single-stranded (ssDNA).

Nonenveloped DNA Virus Families

Adenoviridae (colds, meningitis); Papillomaviridae (warts, cervical cancer); Parvoviridae (fifth disease, gastroenteritis).

Enveloped dsDNA Virus Families

Poxviridae (smallpox); Herpesviridae (cold sores, chickenpox); Hepadnaviridae (Hepatitis B).

RNA Virus Types

Single-stranded (ssRNA) or double-stranded (dsRNA). ssRNA can be positive-sense or negative-sense.

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Positive-Sense ssRNA

Functions as mRNA, allowing direct translation by host ribosomes.

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Nonenveloped Positive-Sense ssRNA

Picornaviridae (common cold, hepatitis A, polio); Caliciviridae (gastroenteritis).

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Enveloped Positive-Sense ssRNA Families

Coronaviridae (SARS); Retroviridae (HIV); Flaviviridae (yellow fever, dengue); Togaviridae (rubella).

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Negative-Sense ssRNA

Must be converted to positive-sense RNA by RNA polymerase before translation.

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Negative-Sense ssRNA Virus Families

Filoviridae (Ebola); Orthomyxoviridae (influenza); Paramyxoviridae (mumps, measles); Arenaviridae (Lassa fever); Bunyaviridae (hantavirus); Rhabdoviridae (rabies).

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dsRNA Virus Family

The family Reoviridae, which is linked to gastroenteritis.

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Why RNA Viruses Mutate Rapidly

RNA polymerase lacks proofreading, leading to rapid mutations and new strains.

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Retrovirus Replication

Retroviruses use reverse transcriptase to produce dsDNA from an ssRNA genome.

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Viral Replication Locations

DNA viruses replicate within the host cell nucleus, while RNA viruses replicate at the host cell ribosomes.

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Study Notes

DNA Classification

  • DNA viruses are categorized into two groups: double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA).
  • dsDNA can be either enveloped or nonenveloped, while ssDNA is exclusively nonenveloped.

Nonenveloped DNA Virus Families

  • Nonenveloped dsDNA families include Adenoviridae (associated with common colds and viral meningitis) and Papillomaviridae (linked to warts and cervical cancer).
  • The only known family in nonenveloped ssDNA is Parvoviridae, which causes fifth disease and gastroenteritis.

Enveloped DNA Virus Families

  • Enveloped dsDNA families are:
    • Poxviridae (responsible for smallpox)
    • Herpesviridae (causes cold sores, chicken pox, shingles, mononucleosis)
    • Hepadnaviridae (includes Hepatitis B and associated liver cancer)

RNA Classification

  • RNA viruses are divided into two types: single-stranded RNA (ssRNA) and double-stranded RNA (dsRNA).
  • ssRNA can be classified further into positive-sense and negative-sense.

Positive-Sense ssRNA Characteristics

  • Positive-sense ssRNA can be either enveloped or nonenveloped and functions as mRNA, enabling direct translation by host ribosomes.
  • Families under positive-sense, nonenveloped ssRNA include:
    • Picornaviridae (causes the common cold, hepatitis A, polio)
    • Caliciviridae (causes gastroenteritis)
  • Enveloped positive-sense ssRNA families consist of:
    • Coronaviridae (includes SARS)
    • Retroviridae (includes HIV)
    • Flaviviridae (includes yellow fever, dengue fever, Zika virus, West Nile fever, hepatitis C)
    • Togaviridae (includes rubella and encephalitis)

Negative-Sense ssRNA Characteristics

  • Negative-sense ssRNA is enveloped and is complementary to mRNA, meaning it must be converted to positive-sense RNA by RNA polymerase before translation can occur.
  • Families of negative-sense, enveloped ssRNA viruses include:
    • Filoviridae (causes Ebola and Marburg disease)
    • Orthomyxoviridae (causes influenza)
    • Paramyxoviridae (includes mumps and measles)
    • Arenaviridae (associated with Lassa fever)
    • Bunyaviridae (associated with hantavirus pulmonary syndrome)
    • Rhabdoviridae (associated with rabies)

Additional RNA Information

  • dsRNA is neither classified as positive nor negative sense and is always nonenveloped.
  • The only known family of dsRNA viruses is Reoviridae, linked to gastroenteritis.

Genome Characteristics and Mutations

  • RNA virus genomes are generally smaller than DNA virus genomes.
  • RNA viruses rely heavily on host cell proteins and enzymes for replication.
  • Higher mutation rates in RNA viruses stem from RNA polymerase's lack of proofreading ability, leading to rapid emergence of new strains.

Retrovirus Definition

  • Retroviruses utilize reverse transcriptase to replicate indirectly through a DNA intermediate, producing dsDNA from an ssRNA genome.

Replication Processes

  • DNA viruses replicate within the host cell, while RNA viruses replicate at the host cell ribosomes.

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