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Questions and Answers
One classification scheme was developed in the 1970s by Nobel laureate ______.
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.
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 ______.
Positive-strand RNA is able to be immediately translated into ______.
proteins
Viruses are only classified using ______, family, genus, and species.
Viruses are only classified using ______, family, genus, and species.
The order taxon ends in ______ suffix.
The order taxon ends in ______ suffix.
The family taxon ends in ______ suffix.
The family taxon ends in ______ suffix.
The genus taxon ends in ______ suffix.
The genus taxon ends in ______ suffix.
The species taxon is generally the ______ name of the virus.
The species taxon is generally the ______ name of the virus.
The Baltimore classification system categorizes the viruses into ______ classes based upon their type of genome:
The Baltimore classification system categorizes the viruses into ______ classes based upon their type of genome:
Viruses with ______ genomes have similar nucleic acid to living organisms:
Viruses with ______ genomes have similar nucleic acid to living organisms:
Phagocytosis is a form of ______ endocytosis that is used by specialized cells to engulf entire cells.
Phagocytosis is a form of ______ endocytosis that is used by specialized cells to engulf entire cells.
The fusion of the viral envelope can occur at the ______ membrane or within endocytosed vesicles, such as the endosome.
The fusion of the viral envelope can occur at the ______ membrane or within endocytosed vesicles, such as the endosome.
Virus’s genome acts as the instructions for the synthesis of virus ______.
Virus’s genome acts as the instructions for the synthesis of virus ______.
The replication strategy of a virus is generally dependent upon the type of ______ acid genome it contains.
The replication strategy of a virus is generally dependent upon the type of ______ acid genome it contains.
Uncoating refers to the breakdown or removal of the ______, causing the release of the virus genome into the cell.
Uncoating refers to the breakdown or removal of the ______, causing the release of the virus genome into the cell.
Rhinoviruses are taken into the cell by ______ endocytosis in clathrin-coated vesicles.
Rhinoviruses are taken into the cell by ______ endocytosis in clathrin-coated vesicles.
Virus genome is copied by ______ protein synthesis to create new virion’s particles.
Virus genome is copied by ______ protein synthesis to create new virion’s particles.
The family Adenoviridae includes the virus ______.
The family Adenoviridae includes the virus ______.
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.
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.
The class of viruses that reverse transcribe includes the family ______.
The class of viruses that reverse transcribe includes the family ______.
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.
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.
Clathrin-mediated ______ is a method of penetration used by viruses such as Dengue virus, hepatitis C virus, and reovirus.
Clathrin-mediated ______ is a method of penetration used by viruses such as Dengue virus, hepatitis C virus, and reovirus.
Viruses with ______ genomes often use the enzymes and proteins that the cell normally uses.
Viruses with ______ genomes often use the enzymes and proteins that the cell normally uses.
Human papillomavirus, hepatitis B virus, use ______-mediated endocytosis as a method of penetration.
Human papillomavirus, hepatitis B virus, use ______-mediated endocytosis as a method of penetration.
During replication, the ______ genome enters the nucleus of the host cell, where the ssDNA is converted to dsDNA by DNA polymerase.
During replication, the ______ genome enters the nucleus of the host cell, where the ssDNA is converted to dsDNA by DNA polymerase.
DsRNA viruses contain an ______ that is carried into the cell within the virion.
DsRNA viruses contain an ______ that is carried into the cell within the virion.
−ssRNA viruses must be transcribed into ______ before translation can occur.
−ssRNA viruses must be transcribed into ______ before translation can occur.
Retroviruses are viruses that reverse transcribe an RNA genome into ______.
Retroviruses are viruses that reverse transcribe an RNA genome into ______.
Reverse transcriptase (RT) is the enzyme that carries out and has the activity of an RNA-dependent DNA polymerase, DNA-dependent DNA polymerase, and ______.
Reverse transcriptase (RT) is the enzyme that carries out and has the activity of an RNA-dependent DNA polymerase, DNA-dependent DNA polymerase, and ______.
Hepatitis B virus is also a retroid virus but instead reverse transcribes in order to create its ______ genome.
Hepatitis B virus is also a retroid virus but instead reverse transcribes in order to create its ______ genome.
Viral nucleic acids are found in a variety of configurations, they can be ______ or circular.
Viral nucleic acids are found in a variety of configurations, they can be ______ or circular.
New strains of virus can occur when two different strains infect one ______.
New strains of virus can occur when two different strains infect one ______.
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 ______.
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 ______.
Reassortment occurs when the ______ segments of segmented viruses are mixed while being packaged into new capsids.
Reassortment occurs when the ______ segments of segmented viruses are mixed while being packaged into new capsids.
Most nonenveloped DNA viruses assemble their nucleocapsid in the ______, since that is the site of genome replication.
Most nonenveloped DNA viruses assemble their nucleocapsid in the ______, since that is the site of genome replication.
Viruses with envelopes derived from the plasma membrane usually assemble at the ______.
Viruses with envelopes derived from the plasma membrane usually assemble at the ______.
Maturation refers to the final changes within an immature ______.
Maturation refers to the final changes within an immature ______.
The HA protein must be cleaved into two portions by cell ______; HA1 and HA2 to become infectious.
The HA protein must be cleaved into two portions by cell ______; HA1 and HA2 to become infectious.
The process of enveloped viruses leaving the cell is known as ______.
The process of enveloped viruses leaving the cell is known as ______.
Lytic viruses, however, disrupt the plasma membrane and cause the ______, or bursting, of the cell.
Lytic viruses, however, disrupt the plasma membrane and cause the ______, or bursting, of the 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 ______.
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 ______.
Reassortment occurs when the genome ______ of segmented viruses are mixed while being packaged into new capsids.
Reassortment occurs when the genome ______ of segmented viruses are mixed while being packaged into new capsids.
New strains of virus can occur when two different strains infect one ______.
New strains of virus can occur when two different strains infect one ______.
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 ______.
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 ______.
Reassortment occurs when the ______ segments of segmented viruses are mixed while being packaged into new capsids.
Reassortment occurs when the ______ segments of segmented viruses are mixed while being packaged into new capsids.
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.
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.
New strains of virus can occur when two different strains infect one ______.
New strains of virus can occur when two different strains infect one ______.
Reassortment occurs when the genome segments of segmented viruses are mixed while being packaged into new ______.
Reassortment occurs when the genome segments of segmented viruses are mixed while being packaged into new ______.
The RdRp jumps from the template of one strain to the template of the other strain during the replication of ______ virus.
The RdRp jumps from the template of one strain to the template of the other strain during the replication of ______ virus.
Viral nucleic acids are found in a variety of configurations, they can be ______ or circular.
Viral nucleic acids are found in a variety of configurations, they can be ______ or circular.
Reassortment occurs when segmented viruses are mixed while being packaged into new ______, resulting in new strains of virus.
Reassortment occurs when segmented viruses are mixed while being packaged into new ______, resulting in new strains of virus.
During replication, the ______ genome enters the nucleus of the host cell, where the ssDNA is converted to dsDNA by DNA polymerase.
During replication, the ______ genome enters the nucleus of the host cell, where the ssDNA is converted to dsDNA by DNA polymerase.
Hepatitis B virus is also a retroid virus but instead reverse transcribes in order to create its ______ genome.
Hepatitis B virus is also a retroid virus but instead reverse transcribes in order to create its ______ genome.
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.
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.
Retroviruses are viruses that reverse transcribe an RNA genome into ______.
Retroviruses are viruses that reverse transcribe an RNA genome into ______.
Reverse transcriptase (RT) is the enzyme that carries out and has the activity of an RNA-dependent DNA polymerase, DNA-dependent DNA polymerase, and ______.
Reverse transcriptase (RT) is the enzyme that carries out and has the activity of an RNA-dependent DNA polymerase, DNA-dependent DNA polymerase, and ______.
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 ______.
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 ______.
Reassortment occurs when the ______ segments of segmented viruses are mixed while being packaged into new capsids.
Reassortment occurs when the ______ segments of segmented viruses are mixed while being packaged into new capsids.
The replication strategy of a virus is generally dependent upon the type of ______ acid genome it contains.
The replication strategy of a virus is generally dependent upon the type of ______ acid genome it contains.
New strains of virus can occur when two different strains infect one ______.
New strains of virus can occur when two different strains infect one ______.
Viral nucleic acids are found in a variety of configurations, they can be ______ or circular.
Viral nucleic acids are found in a variety of configurations, they can be ______ or circular.
The Baltimore classification system categorizes the viruses into seven classes based upon their type of ______ genome.
The Baltimore classification system categorizes the viruses into seven classes based upon their type of ______ genome.
Class VII: DNA viruses that ______ transcribe include the family Hepadnaviridae.
Class VII: DNA viruses that ______ transcribe include the family Hepadnaviridae.
Class VI: RNA viruses that ______ transcribe include the family Retroviridae.
Class VI: RNA viruses that ______ transcribe include the family Retroviridae.
During replication, the ______ genome enters the nucleus of the host cell, where the ssDNA is converted to dsDNA by DNA polymerase.
During replication, the ______ genome enters the nucleus of the host cell, where the ssDNA is converted to dsDNA by DNA polymerase.
DsRNA viruses contain an ______ that is carried into the cell within the virion.
DsRNA viruses contain an ______ that is carried into the cell within the virion.
-ssRNA viruses must be transcribed into ______ before translation can occur.
-ssRNA viruses must be transcribed into ______ before translation can occur.
Retroviruses are viruses that reverse transcribe an RNA genome into ______.
Retroviruses are viruses that reverse transcribe an RNA genome into ______.
Reverse transcriptase (RT) is the enzyme that carries out and has the activity of an RNA-dependent DNA polymerase, DNA-dependent DNA polymerase, and ______.
Reverse transcriptase (RT) is the enzyme that carries out and has the activity of an RNA-dependent DNA polymerase, DNA-dependent DNA polymerase, and ______.
Hepatitis B virus is also a retroid virus but instead reverse transcribes in order to create its ______ genome.
Hepatitis B virus is also a retroid virus but instead reverse transcribes in order to create its ______ genome.
Viral nucleic acids are found in a variety of configurations, they can be ______ or circular.
Viral nucleic acids are found in a variety of configurations, they can be ______ or circular.
New strains of virus can occur when two different strains infect one ______.
New strains of virus can occur when two different strains infect one ______.
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.
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.
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.
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.
Most nonenveloped DNA viruses assemble their nucleocapsid in the _______, since that is the site of genome replication.
Most nonenveloped DNA viruses assemble their nucleocapsid in the _______, since that is the site of genome replication.
Viruses with envelopes derived from the plasma membrane usually assemble at the ______.
Viruses with envelopes derived from the plasma membrane usually assemble at the ______.
Maturation refers to the final changes within an immature ______ particle.
Maturation refers to the final changes within an immature ______ particle.
The HA protein must be cleaved into two portions by cell ______; HA1 and HA2 to become infectious.
The HA protein must be cleaved into two portions by cell ______; HA1 and HA2 to become infectious.
Lytic viruses, however, disrupt the plasma membrane and cause the _______, or bursting, of the cell.
Lytic viruses, however, disrupt the plasma membrane and cause the _______, or bursting, of the cell.
The process of enveloped viruses leaving the cell is known as ______.
The process of enveloped viruses leaving the cell is known as ______.
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 ______.
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 ______.
The Baltimore classification system categorizes the viruses into seven classes based upon their type of ______ genome.
The Baltimore classification system categorizes the viruses into seven classes based upon their type of ______ genome.
Class VII: ______ viruses that reverse transcribe.
Class VII: ______ viruses that reverse transcribe.
Retroviridae is a family of viruses that reverse transcribe an RNA genome into ______.
Retroviridae is a family of viruses that reverse transcribe an RNA genome into ______.
Hepadnaviridae is a family of ______ viruses that reverse transcribe.
Hepadnaviridae is a family of ______ viruses that reverse transcribe.
Reverse transcriptase (RT) is the enzyme that carries out and has the activity of an RNA-dependent DNA polymerase, DNA-dependent DNA polymerase, and ______.
Reverse transcriptase (RT) is the enzyme that carries out and has the activity of an RNA-dependent DNA polymerase, DNA-dependent DNA polymerase, and ______.
Hepatitis B virus is also a retroid virus but instead reverse transcribes in order to create its ______ genome.
Hepatitis B virus is also a retroid virus but instead reverse transcribes in order to create its ______ genome.
Retroviruses are viruses that reverse transcribe an RNA genome into ______.
Retroviruses are viruses that reverse transcribe an RNA genome into ______.
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:
- Double-stranded DNA viruses
- Single-stranded DNA viruses
- Double-stranded RNA viruses
- Positive-sense RNA viruses
- Negative-sense RNA viruses
- RNA viruses that reverse transcribe
- 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.
