Chapter 6
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139 Terms
Q. Where do most DNA viruses replicate?
In the nucleus.
Q. What exception to the usual DNA-virus replication location is emphasized in the study guide?
Poxviruses replicate in the cytoplasm.
Q. Where do most RNA viruses replicate?
In the cytoplasm, using their own RNA-dependent RNA polymerase.
Q. Which RNA viruses are exceptions to the usual cytoplasmic replication location?
Influenza viruses and retroviruses; they involve the nucleus.
Q. What does a DNA virus use for transcription?
Host RNA polymerase.
Q. What can DNA viruses use for genome replication?
Host or viral DNA polymerase.
Q. What enzyme do RNA viruses use to replicate their RNA genomes?
RNA-dependent RNA polymerase (RdRp).
Q. How are naked viruses generally released from an infected cell?
Through cell death.
Q. How are enveloped viruses generally released from an infected cell?
By budding.
Q. Where do most enveloped viruses bud from?
The plasma membrane.
Q. From which membrane do herpesviruses bud, according to the study guide?
The nuclear membrane.
Q. From which cellular location do poxviruses bud?
The Golgi.
Q. How can viral mutation and recombination benefit viruses?
They help viruses evade the host immune system.
Q. Why can latent viruses be difficult to eliminate with antiviral drugs?
They can remain in the host, sometimes within the host genome, with little or no viral production.
Q. What are viroids?
Circular RNA molecules without a protein shell that cause plant diseases.
Q. What are prions?
Infectious protein particles that contain no genes.
Q. What diseases are associated with prions?
Scrapie, bovine spongiform encephalopathy (BSE), kuru, Creutzfeldt-Jakob disease (CJD), and Gerstmann-Sträussler-Scheinker disease.
Q. What type of genetic material does a virus contain?
Either DNA or RNA, never both.
Q. What are the possible forms of a viral genome?
Single-stranded or double-stranded, linear or circular, and segmented or nonsegmented.
Q. What are the three possible RNA genome orientations described in the study guide?
Positive-sense (+), negative-sense (−), and ambisense.
Q. What are the two major viral capsid shapes?
Helical and icosahedral.
Q. What is an icosahedral capsid?
A geometric structure with 12 vertices, 20 faces, and 30 edges.
Q. What are capsomeres?
Protein units that make up the viral capsid; they may contain five or six protein units.
Q. What is the capsid?
The protein coat surrounding and protecting the viral genome.
Q. What are the functions of the capsid and envelope?
They protect the viral genome, help with entry into host cells, and may carry enzymes.
Q. What is a viral envelope?
A membrane surrounding the viral capsid.
Q. What are envelope spikes also called?
Peplomers or glycoproteins.
Q. What are the functions of viral envelope spikes?
They bind host-cell receptors, help with membrane fusion, and serve as major antigens recognized by the immune system.
Q. What happens when antibodies bind to viral spikes?
They can neutralize the virus by blocking attachment or entry.
Q. What is the function of the matrix protein in an enveloped virus?
It bridges the nucleocapsid and the envelope.
Q. What is the nucleocapsid?
The viral genome together with its surrounding capsid.
Q. Approximately how small can viruses be?
About 20 nm; parvovirus is an example.
Q. Approximately how large can human viruses be?
About 300 nm; poxvirus is an example.
Q. What is one physical property that helps distinguish viruses from bacteria?
Viruses can pass through filters that stop bacteria.
Q. What is the genome and structure of Picornaviridae?
Positive-sense single-stranded RNA (+ssRNA); naked and icosahedral.
Q. What are examples of Picornaviridae?
Poliovirus, coxsackievirus, echovirus, hepatitis A virus (HAV), and rhinovirus.
Q. What is the genome and structure of Caliciviridae?
+ssRNA; naked.
Q. What is an important member of Caliciviridae?
Norovirus, also called Norwalk virus.
Q. What is the genome and structure of Hepeviridae?
+ssRNA; naked.
Q. What is an important member of Hepeviridae?
Hepatitis E virus (HEV).
Q. What is the genome and structure of Astroviridae?
+ssRNA; naked.
Q. What is an important member of Astroviridae?
Astrovirus.
Q. What is the genome and structure of Flaviviridae?
+ssRNA; enveloped.
Q. What are examples of Flaviviridae?
Dengue virus, yellow fever virus, West Nile virus, Zika virus, and hepatitis C virus (HCV).
Q. What is the genome and structure of Togaviridae?
+ssRNA; enveloped and icosahedral.
Q. What are examples of Togaviridae?
Rubella virus (Rubivirus), equine encephalitis viruses, and chikungunya virus.
Q. What is the genome and structure of Coronaviridae?
+ssRNA; enveloped with a helical nucleocapsid.
Q. What distinction does the study guide make about coronavirus genomes?
Coronaviruses have the largest RNA virus genomes.
Q. What are examples of Coronaviridae?
Common cold coronaviruses, SARS-CoV-1, SARS-CoV-2, and MERS-CoV.
Q. What is the genome and structure of Retroviridae?
Positive-sense RNA, diploid (two copies of the genome), and enveloped.
Q. What are examples of Retroviridae?
HIV and HTLV.
Q. What is the genome and structure of Deltaviridae?
Negative-sense circular single-stranded RNA; enveloped.
Q. What is an important member of Deltaviridae?
Hepatitis D virus (HDV).
Q. What is the genome and structure of Orthomyxoviridae?
Negative-sense single-stranded RNA with eight segments; enveloped and helical.
Q. What are examples of Orthomyxoviridae?
Influenza A, B, and C.
Q. What is the genome and structure of Paramyxoviridae?
Negative-sense single-stranded RNA; enveloped and helical.
Q. What are examples of Paramyxoviridae?
Mumps, measles, RSV, parainfluenza, and human metapneumovirus (hMPV).
Q. What is the genome and structure of Rhabdoviridae?
Negative-sense single-stranded RNA; enveloped and helical.
Q. What is an important member of Rhabdoviridae?
Rabies virus.
Q. What is the genome and structure of Filoviridae?
Negative-sense single-stranded RNA; enveloped.
Q. What are examples of Filoviridae?
Ebola and Marburg viruses.
Q. What is the genome and structure of Bunyaviridae?
Three RNA segments with negative- or positive-sense RNA; enveloped.
Q. What is an important member of Bunyaviridae?
Hantavirus.
Q. What is the genome and structure of Reoviridae?
Double-stranded RNA with 10 segments; naked.
Q. What is an important member of Reoviridae?
Rotavirus.
Q. What is the genome and structure of Parvoviridae?
Single-stranded DNA (ssDNA); naked and approximately 20 nm.
Q. What are examples of Parvoviridae?
Parvovirus B19 and bocavirus.
Q. What is the genome and structure of Hepadnaviridae?
Partially double-stranded circular DNA; enveloped.
Q. What is an important member of Hepadnaviridae?
Hepatitis B virus (HBV).
Q. What is the genome and structure of Papillomaviridae?
Circular double-stranded DNA (dsDNA); naked.
Q. What is an important member of Papillomaviridae?
Human papillomavirus (HPV).
Q. What is the genome and structure of Polyomaviridae?
Circular double-stranded DNA; naked.
Q. What are examples of Polyomaviridae?
JC virus and BK virus.
Q. What is the genome and structure of Adenoviridae?
Linear double-stranded DNA; naked.
Q. What is an important member of Adenoviridae?
Adenovirus.
Q. What is the genome and structure of Herpesviridae?
Linear double-stranded DNA; enveloped.
Q. What are examples of Herpesviridae?
HSV-1, HSV-2, VZV, EBV, CMV, and HHV-6, HHV-7, and HHV-8.
Q. What is the genome and structure of Poxviridae?
Linear double-stranded DNA; enveloped and brick-shaped.
Q. What are examples of Poxviridae?
Smallpox virus and molluscum contagiosum virus.
Q. Which DNA virus family replicates in the cytoplasm?
Poxviridae.
Q. Which DNA virus families encode their own DNA polymerase, according to the study guide?
Herpesviridae and Adenoviridae.
Q. Which DNA virus is identified as an exception to the ability of DNA viruses to transform host cells?
Parvovirus.
Q. What is the general rule for negative-sense RNA viruses?
They are enveloped and carry their own RNA-dependent RNA polymerase.
Q. Why must a negative-sense RNA virus carry its own polymerase?
Host cells cannot directly translate negative-sense RNA into proteins; the viral polymerase must make mRNA.
Q. What can positive-sense RNA do once it enters a host cell?
It can act directly as mRNA and be translated.
Q. How are positive-sense RNA viral proteins commonly produced?
The genome is translated as a polyprotein, which is then cleaved by proteases.
Q. What enzyme may be included among the proteins produced from a positive-sense RNA viral polyprotein?
RNA-dependent RNA polymerase (RdRp).
Q. How does a double-stranded RNA virus make mRNA?
Its viral polymerase makes mRNA from the RNA genome; it follows the negative-sense RNA strategy.
Q. What must happen to a single-stranded DNA genome before it can be transcribed?
It must first be converted into double-stranded DNA.
Q. What is the general replication pathway for double-stranded DNA viruses?
DNA is transcribed into mRNA in the nucleus using host machinery, except for poxviruses, which replicate in the cytoplasm.
Q. How does a retrovirus use its positive-sense RNA genome?
Reverse transcriptase converts the RNA into complementary DNA, which becomes double-stranded DNA and integrates into the host genome.
Q. Which two virus groups are important exceptions to the usual replication-location rules?
Poxviruses replicate in the cytoplasm despite being DNA viruses; influenza and retroviruses involve the nucleus despite being RNA viruses.
Q. What are the six steps of the viral replication cycle in order?
- Adsorption/attachment 2. Penetration/entry 3. Uncoating 4. Synthesis of components 5. Assembly 6. Release.
Q. What is adsorption in viral replication?
Attachment of the virus to a host-cell receptor.
Q. What determines a virus's host range and tissue tropism?
The receptors the virus can bind on host cells.
Q. What is tissue tropism?
The preference or ability of a virus to infect particular cell types or tissues.
Q. What is penetration in viral replication?
The entry of the virus or its genome into the host cell.
Q. What is uncoating?
Removal of the viral capsid or other protective structures to release the viral genome inside the host cell.
Q. What is the most important step of viral replication emphasized in the study guide?
Synthesis of viral mRNA, proteins, and genomes.
Q. What happens during viral assembly?
Newly made viral genomes and structural proteins are put together to form new virions.