Virus Classification and Taxonomy

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Questions and Answers

One classification scheme was developed in the 1970s by Nobel laureate ______.

David Baltimore

The Baltimore classification system categorizes viruses based on the type of ______ acid genome and replication strategy of the virus.

nucleic

Positive-strand RNA is able to be immediately translated into ______.

proteins

Viruses are only classified using ______, family, genus, and species.

order Signup and view all the answers

The order taxon ends in ______ suffix.

-virales Signup and view all the answers

The family taxon ends in ______ suffix.

-viridae Signup and view all the answers

The genus taxon ends in ______ suffix.

-virus Signup and view all the answers

The species taxon is generally the ______ name of the virus.

common Signup and view all the answers

The Baltimore classification system categorizes the viruses into ______ classes based upon their type of genome:

seven Signup and view all the answers

Viruses with ______ genomes have similar nucleic acid to living organisms:

dsDNA Signup and view all the answers

Phagocytosis is a form of ______ endocytosis that is used by specialized cells to engulf entire cells.

receptor-mediated Signup and view all the answers

The fusion of the viral envelope can occur at the ______ membrane or within endocytosed vesicles, such as the endosome.

cell Signup and view all the answers

Virus’s genome acts as the instructions for the synthesis of virus ______.

proteins Signup and view all the answers

The replication strategy of a virus is generally dependent upon the type of ______ acid genome it contains.

nucleic Signup and view all the answers

Uncoating refers to the breakdown or removal of the ______, causing the release of the virus genome into the cell.

capsid Signup and view all the answers

Rhinoviruses are taken into the cell by ______ endocytosis in clathrin-coated vesicles.

receptor-mediated Signup and view all the answers

Virus genome is copied by ______ protein synthesis to create new virion’s particles.

replication Signup and view all the answers

The family Adenoviridae includes the virus ______.

Adenovirus Signup and view all the answers

Within the acidic endosome, the virus expands in size about ______%, and one of the capsid proteins, VP1, forms pores in the endosome that allow the release of the rhinovirus RNA genome.

4 Signup and view all the answers

The class of viruses that reverse transcribe includes the family ______.

Retroviridae Signup and view all the answers

The binding of the poliovirus capsid to the cell surface receptor causes a conformational change in the ______ that creates a pore in the cell membrane.

virion Signup and view all the answers

Clathrin-mediated ______ is a method of penetration used by viruses such as Dengue virus, hepatitis C virus, and reovirus.

endocytosis Signup and view all the answers

Viruses with ______ genomes often use the enzymes and proteins that the cell normally uses.

dsDNA Signup and view all the answers

Human papillomavirus, hepatitis B virus, use ______-mediated endocytosis as a method of penetration.

caveolin Signup and view all the answers

During replication, the ______ genome enters the nucleus of the host cell, where the ssDNA is converted to dsDNA by DNA polymerase.

ssDNA Signup and view all the answers

DsRNA viruses contain an ______ that is carried into the cell within the virion.

RdRp Signup and view all the answers

−ssRNA viruses must be transcribed into ______ before translation can occur.

vmRNA Signup and view all the answers

Retroviruses are viruses that reverse transcribe an RNA genome into ______.

cDNA Signup and view all the answers

Reverse transcriptase (RT) is the enzyme that carries out and has the activity of an RNA-dependent DNA polymerase, DNA-dependent DNA polymerase, and ______.

RNase H Signup and view all the answers

Hepatitis B virus is also a retroid virus but instead reverse transcribes in order to create its ______ genome.

DNA Signup and view all the answers

Viral nucleic acids are found in a variety of configurations, they can be ______ or circular.

linear Signup and view all the answers

New strains of virus can occur when two different strains infect one ______.

cell Signup and view all the answers

Recombination occurs when the genome of an RNA virus is being replicated and the RdRp jumps from the template of one strain to the template of the other strain, creating a hybrid ______.

genome Signup and view all the answers

Reassortment occurs when the ______ segments of segmented viruses are mixed while being packaged into new capsids.

genome Signup and view all the answers

Most nonenveloped DNA viruses assemble their nucleocapsid in the ______, since that is the site of genome replication.

nucleus Signup and view all the answers

Viruses with envelopes derived from the plasma membrane usually assemble at the ______.

plasma membrane Signup and view all the answers

Maturation refers to the final changes within an immature ______.

virion Signup and view all the answers

The HA protein must be cleaved into two portions by cell ______; HA1 and HA2 to become infectious.

proteases Signup and view all the answers

The process of enveloped viruses leaving the cell is known as ______.

budding Signup and view all the answers

Lytic viruses, however, disrupt the plasma membrane and cause the ______, or bursting, of the cell.

lysis Signup and view all the answers

Recombination occurs when the genome of an RNA virus is being replicated and the RdRp jumps from the template of one strain to the template of the other strain, creating a hybrid ______.

genome Signup and view all the answers

Reassortment occurs when the genome ______ of segmented viruses are mixed while being packaged into new capsids.

segments Signup and view all the answers

New strains of virus can occur when two different strains infect one ______.

cell Signup and view all the answers

Recombination occurs when the genome of an RNA virus is being replicated and the RdRp jumps from the template of one strain to the template of the other strain, creating a hybrid ______.

genome Signup and view all the answers

Reassortment occurs when the ______ segments of segmented viruses are mixed while being packaged into new capsids.

genome Signup and view all the answers

Recombination occurs when the RdRp jumps from the template of one strain to the template of the other strain, creating a hybrid ______ during genome replication.

genome Signup and view all the answers

New strains of virus can occur when two different strains infect one ______.

cell Signup and view all the answers

Reassortment occurs when the genome segments of segmented viruses are mixed while being packaged into new ______.

capsids Signup and view all the answers

The RdRp jumps from the template of one strain to the template of the other strain during the replication of ______ virus.

RNA Signup and view all the answers

Viral nucleic acids are found in a variety of configurations, they can be ______ or circular.

linear Signup and view all the answers

Reassortment occurs when segmented viruses are mixed while being packaged into new ______, resulting in new strains of virus.

capsids Signup and view all the answers

During replication, the ______ genome enters the nucleus of the host cell, where the ssDNA is converted to dsDNA by DNA polymerase.

ssDNA Signup and view all the answers

Hepatitis B virus is also a retroid virus but instead reverse transcribes in order to create its ______ genome.

DNA Signup and view all the answers

Recombination occurs when the genome of an RNA virus is being replicated and the RdRp jumps from the template of one strain to the template of the other strain, creating a hybrid ______, resulting in new strains of virus.

genome Signup and view all the answers

Retroviruses are viruses that reverse transcribe an RNA genome into ______.

cDNA Signup and view all the answers

Reverse transcriptase (RT) is the enzyme that carries out and has the activity of an RNA-dependent DNA polymerase, DNA-dependent DNA polymerase, and ______.

RNase H Signup and view all the answers

Recombination occurs when the genome of an RNA virus is being replicated and the RdRp jumps from the template of one strain to the template of the other strain, creating a hybrid ______.

genome Signup and view all the answers

Reassortment occurs when the ______ segments of segmented viruses are mixed while being packaged into new capsids.

genomic Signup and view all the answers

The replication strategy of a virus is generally dependent upon the type of ______ acid genome it contains.

nucleic Signup and view all the answers

New strains of virus can occur when two different strains infect one ______.

cell Signup and view all the answers

Viral nucleic acids are found in a variety of configurations, they can be ______ or circular.

linear Signup and view all the answers

The Baltimore classification system categorizes the viruses into seven classes based upon their type of ______ genome.

nucleic acid Signup and view all the answers

Class VII: DNA viruses that ______ transcribe include the family Hepadnaviridae.

reverse Signup and view all the answers

Class VI: RNA viruses that ______ transcribe include the family Retroviridae.

reverse Signup and view all the answers

During replication, the ______ genome enters the nucleus of the host cell, where the ssDNA is converted to dsDNA by DNA polymerase.

ssDNA Signup and view all the answers

DsRNA viruses contain an ______ that is carried into the cell within the virion.

RdRp Signup and view all the answers

-ssRNA viruses must be transcribed into ______ before translation can occur.

vmRNA Signup and view all the answers

Retroviruses are viruses that reverse transcribe an RNA genome into ______.

cDNA Signup and view all the answers

Reverse transcriptase (RT) is the enzyme that carries out and has the activity of an RNA-dependent DNA polymerase, DNA-dependent DNA polymerase, and ______.

RNase H Signup and view all the answers

Hepatitis B virus is also a retroid virus but instead reverse transcribes in order to create its ______ genome.

rcDNA Signup and view all the answers

Viral nucleic acids are found in a variety of configurations, they can be ______ or circular.

linear Signup and view all the answers

New strains of virus can occur when two different strains infect one ______.

cell Signup and view all the answers

Recombination occurs when the genome of an RNA virus is being replicated and the RdRp jumps from the template of one strain to the template of the other strain, creating a hybrid ______ genome.

RNA Signup and view all the answers

Viruses components must be collected at a particular site of the cell and undergo assembly to form an immature virus particle, it can take place within the nucleus of the cell, at the plasma membrane, or at a variety of intracellular membranes, such as the ______ complex.

Golgi Signup and view all the answers

Most nonenveloped DNA viruses assemble their nucleocapsid in the _______, since that is the site of genome replication.

nucleus Signup and view all the answers

Viruses with envelopes derived from the plasma membrane usually assemble at the ______.

plasma membrane Signup and view all the answers

Maturation refers to the final changes within an immature ______ particle.

virion Signup and view all the answers

The HA protein must be cleaved into two portions by cell ______; HA1 and HA2 to become infectious.

proteases Signup and view all the answers

Lytic viruses, however, disrupt the plasma membrane and cause the _______, or bursting, of the cell.

lysis Signup and view all the answers

The process of enveloped viruses leaving the cell is known as ______.

budding Signup and view all the answers

Viruses with dsDNA genomes have similar nucleic acid to living organisms and often use the enzymes and proteins that the cell normally uses including its DNA polymerases and RNA polymerases; are located in the ______.

nucleus Signup and view all the answers

The Baltimore classification system categorizes the viruses into seven classes based upon their type of ______ genome.

nucleic acid Signup and view all the answers

Class VII: ______ viruses that reverse transcribe.

DNA Signup and view all the answers

Retroviridae is a family of viruses that reverse transcribe an RNA genome into ______.

DNA Signup and view all the answers

Hepadnaviridae is a family of ______ viruses that reverse transcribe.

DNA Signup and view all the answers

Reverse transcriptase (RT) is the enzyme that carries out and has the activity of an RNA-dependent DNA polymerase, DNA-dependent DNA polymerase, and ______.

RNase H Signup and view all the answers

Hepatitis B virus is also a retroid virus but instead reverse transcribes in order to create its ______ genome.

dsDNA Signup and view all the answers

Retroviruses are viruses that reverse transcribe an RNA genome into ______.

DNA Signup and view all the answers

Study Notes

Virus Classification and Taxonomy

The Baltimore classification system categorizes viruses based on their type of nucleic acid genome and replication strategy.
The system uses four taxonomic ranks: order, family, genus, and species.
Only about half of viruses are currently classified in orders.
Family names end in -viridae, and sub-families are indicated with -virinae suffix.
Genus names end in -virus suffix.
Species names are generally the "common name" of the virus.

Virus Replication

The replication strategy of a virus depends on the type of nucleic acid genome it contains.
There are seven classes of viruses based on their replication strategy:
Class I: Double-stranded DNA (dsDNA) viruses
Class II: Single-stranded DNA (ssDNA) viruses
Class III: Double-stranded RNA (dsRNA) viruses
Class IV: Positive-sense RNA viruses
Class V: Negative-sense RNA viruses
Class VI: RNA viruses that reverse transcribe
Class VII: DNA viruses that reverse transcribe
Viruses with dsDNA genomes use the enzymes and proteins of the host cell, including DNA polymerases and RNA polymerases.
RNA genomes do not enter the nucleus of the host cell.
dsRNA viruses contain an RNA-dependent RNA polymerase (RdRp) that is carried into the cell within the virion.
Positive-sense RNA viruses have infectious genomes, while negative-sense RNA viruses are not infectious and must be transcribed into viral mRNA before translation.
Retroviruses reverse transcribe an RNA genome into complementary DNA (cDNA).
Hepatitis B virus is a retroid virus that reverse transcribes an RNA genome into partially double-stranded and partially single-stranded DNA (rcDNA).

Virus Replication Strategies

Viral nucleic acids can be linear or circular, and can be segmented into several smaller pieces within the virion.
New strains of virus can occur when two different strains infect one cell.
Recombination occurs when the genome of an RNA virus is being replicated and the RdRp jumps from the template of one strain to the template of the other strain, creating a hybrid genome.
Reassortment occurs when the genome segments of segmented viruses are mixed while being packaged into new capsids.

Assembly and Maturation

Assembly of viral components takes place at a particular site of the cell, such as the nucleus, plasma membrane, or Golgi complex.
Most non-enveloped DNA viruses assemble their nucleocapsid in the nucleus.
Viruses with envelopes derived from the plasma membrane usually assemble at the plasma membrane.
Maturation refers to the final changes within an immature virion, often involving structural capsid changes.
Example: Influenza HA protein must be cleaved into two portions by cell proteases to become infectious.

Release

Release is the final step in the viral replication cycle.
For enveloped viruses, release occurs by budding from the plasma membrane, which is then wrapped around the virus and leaves the cell through exocytosis.
Non-enveloped viruses can also exit the cell via exocytosis.
Lytic viruses, however, disrupt the plasma membrane and cause the lysis, or bursting, of the cell.

Replication and Assembly of Viruses

Recombination: RNA virus genome replication, RdRp jumps from one strain's template to another, creating a hybrid genome.
Reassortment: mixing of genome segments of segmented viruses during packaging into new capsids.

Assembly of Viruses

Assembly occurs at specific sites in the cell, such as the nucleus, plasma membrane, or intracellular membranes (e.g., Golgi complex).
Non-enveloped DNA viruses assemble nucleocapsid in the nucleus, where genome replication occurs.
Enveloped viruses derive from the plasma membrane and assemble there.

Maturation of Viruses

Final changes occur in immature virions, involving structural capsid changes.
Example: influenza HA protein cleavage into HA1 and HA2 by cell proteases, allowing infectious virus formation.

Release of Viruses

Enveloped viruses bud from the plasma membrane, undergoing exocytosis to leave the cell.
Non-enveloped viruses exit the cell via exocytosis or lytic release, causing cell lysis.

Genome Replication

Viral nucleic acids can be linear or circular, segmented or non-segmented.
Replication strategy depends on the type of nucleic acid genome (e.g., DNA, RNA, etc.).

Baltimore Classification System

Class I: Double-stranded DNA viruses
Class II: Single-stranded DNA viruses
Class III: Double-stranded RNA viruses
Class IV: Positive-sense RNA viruses
Class V: Negative-sense RNA viruses
Class VI: RNA viruses that reverse transcribe
Class VII: DNA viruses that reverse transcribe

Virus Replication

All dsDNA viruses that infect humans enter the nucleus of the cell, while RNA genomes do not.
Replication of ssDNA genome:
- Enters the nucleus of the host cell
- Converted to dsDNA by DNA polymerase
Replication of dsRNA viruses:
- Carries RdRp into the cell within the virion
- RdRp converts ssRNA to dsRNA

Positive-Sense RNA Viruses

Genome is infectious and can be directly translated by ribosomes
No need for RNA-dependent RNA polymerase (RdRp)

Negative-Sense RNA Viruses

Genome is not infectious and must be transcribed into vmRNA before translation
Carries RdRp into the cell to transcribe vmRNA

Retroviruses

Reverse transcribe RNA genome into cDNA using reverse transcriptase (RT)
RT has activities of RNA-dependent DNA polymerase, DNA-dependent DNA polymerase, and RNase H
Transcription and genome replication is carried out by host enzymes

Hepatitis B Virus

Reverse transcribes to create its DNA genome, which is partially single-stranded and partially double-stranded (rcDNA)
rcDNA is repaired to a completely double-stranded episome (cccDNA) in the nucleus of the cell
RNA polymerase II transcribes an RNA pregenome that is reverse transcribed into the rcDNA genome

Baltimore Classification System

Classifies viruses into seven classes based on their type of genome:
1. Double-stranded DNA viruses
2. Single-stranded DNA viruses
3. Double-stranded RNA viruses
4. Positive-sense RNA viruses
5. Negative-sense RNA viruses
6. RNA viruses that reverse transcribe
7. DNA viruses that reverse transcribe

Families of Human Viruses

Class I: dsDNA viruses (e.g., Adenoviridae, Herpesviridae, Poxviridae)
Class II: ssDNA viruses (e.g., Parvoviridae)
Class III: dsRNA viruses (e.g., Reoviridae)
Class IV: +ssRNA viruses (e.g., Coronaviridae, Hepeviridae, Picornaviridae)
Class V: -ssRNA viruses (e.g., Filoviridae, Orthomyxoviridae, Paramyxoviridae)
Class VI: RNA viruses that reverse transcribe (e.g., Retroviridae)
Class VII: DNA viruses that reverse transcribe (e.g., Hepadnaviridae)

Virus Assembly and Release

Assembly occurs at specific sites in the cell (nucleus, plasma membrane, or intracellular membranes)
Nonenveloped DNA viruses assemble their nucleocapsid in the nucleus
Viruses with envelopes derived from the plasma membrane usually assemble there
Maturation involves structural capsid changes (e.g., influenza HA protein)
Release occurs through budding (enveloped viruses) or exocytosis (nonenveloped viruses)

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Description

Learn about the Baltimore classification system, which categorizes viruses based on their genetic material and replication strategy, and understand the different taxonomic ranks used to classify viruses.