Replication of Viruses Flashcards
Nuclear Spread of Virus Genome
Viral genome is integrated into the host cell genome and passed down to next progeny or generation of host cell
Assembly and Maturation
Assembly of virus genome and proteins into new virions follows a specific order, all components are packaged to form mature virions
Result of splicing
mRNA having different coding information derived from a single gene
Burst Size
Number of infectious virions released per average cell
Fusion Proteins
Found on the surface of the virus, facilitate membrane fusion
Adsorption
During this period, virus attaches to and enters the cells, and the titer of free virus in the medium may actually decline
Intercellular Spread
Spread from cell to cell without contact with extracellular environment
Replication of (+) single stranded RNA with Reverse Transcriptase
- (+)ssRNA → RNA Dependent DNA Polymerase → (-) ssDNA → DNA Dependent DNA Polymerase → dsDNA Intermediate
- (-)dsDNA Intermediate → DNA Dependent RNA Polymerase → (+)mRNA → Viral Protein
- (-)dsDNA Intermediate → DNA Dependent RNA Polymerase → (+)ssRNA → Viral Genome
Exocytosis
Vesicles containing virus migrate to plasma membrane and released
Replication of (+) single strand RNA
- (+)ssRNA → Translates Directly → (+) mRNA → Viral Protein
- (+)ssRNA → RNA Dependent RNA polymerase → (-)ssRNA
- (-)ssRNA → RNA Dependent RNA Polymerase → (+) mRNA → Viral Protein
- (-)ssRNA → RNA Dependent RNA Polymerase → (+)ssRNA
Mechanisms of intercellular transmission of viruses
Cell to Cell plasma membrane fusion
Passage across tight junction
Movement across a neural synapse
VIral induction of actin or tubulin
Subversion of actin containing structures form filopodial bridges
Membrane nanotube subversion
Virological synapse
Monocistronic mRNA
mRNA that encodes one polypeptide
Co-Receptor
Additional cell surface molecule required for entry when binding to a cellular receptor is not sufficient for infection
Exon
Portion of a gene that encods for amino acids
Replication of double stranded RNA
- (-)dsRNA → RNA Dependent RNA Polymerase → (+) mRNA → Viral Protein
- dsRNA → RNA Dependent RNA Polymerase → dsRNA → Viral Genome
Pore-Mediated Penetration
Inject their genome into the host cytoplasm throug the creation of a pore in the host membrane
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Non-Enveloped Viruses
Eclipse Period
Time interval between uncoating (disappearance of viruses) and appearance intracellularly of first infectious progeny virions.
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No infectious virus can be detected
Steps of Virus Replication
Attachment
Penetration
Uncoating
Synthesis of Viral Components
Assembly and Maturation
Release
Viral Protein and Nucleic Acid Synthesis
Flow of genetic information in eukaryotic cell
Function of the PolyA Tail
Interact with polyA binding protein - translation
Splicing
Process that removes introns and joins exons in primary transcript
Lysis occurs when a viral capsid induces ruptrue of endosomal membrane, releasing viral capsid or genome in (enveloped/nonenveloped) viruses
Non Enveloped
Endocytosis
Process involves invagination and pinching off of small regions of teh cell membrane, resulting in the non-specific internalization of molecules
3’ Polyadenylation
Stretch of adenylate residues are added to the 3’ end
Type of Endocytosis that uses specialized lipid rafts
Caveolin-Mediated Endocytosis
Extracellular Spread
Released viruses in extracellular environment travel to new cell, same replication cycle occurs
Clathrin-Mediated Endocytosis
- Virion attachment to host cell receptor induces binding of adaptor protein
- Adaptor protein bind Clathrin
- Clathrin-Coated Pit forms
- Dynamin pinch off Clathrin-Coated Pit from host membrane creating a Clathrin coated vesicle
- Clathrin basket released from vesicle
- Vesicle delivers viral components to endosome
- pH of endosome becomes acidic and viral genome is released
Intron
Portion of gene that does not code for amino acids
Capping
Additon of 7-methylguanosine to the 5’ end of RNA
Receptor
Structure on the surface of a cell (or inside a cell) that selectively receives and binds a specific substance and mediates its entry or action into the cell
Alternative Splicing
All introns spliced out, only select exons spliced in
Latent Period
Time before new infectious virus appears in the medium
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No extracellular virions detected
pH Independent Fusion Proteins
- Fusion protein catalyzes membrane fusion at the cell surface at neutral pH
- Viral nucleocapsid is released into the cytoplasm
Functions of the 5’ Cap
Adds stability to the mRNA
Binding of mRNA to ribosomes
Marks mRNA as self
Permissive Cell
Cell in which a virus is able to replicate
Replication of (-) single strand RNA
- (-)ssRNA → RNA Dependent RNA Polymerase → (+) mRNA → Viral Protein
- (-)ssRNA → RNA Dependent RNA Polymerase → (+) ssRNA → RNA Dependent RNA Polymerase → (-)ssRNA → Viral genome
Non-Permissive Cell
Cells in which a factor or factors necessary to viral replication is not present or one detrimental to viral replication is present
Surface Fusion
Enveloped virus fuses with the surface of the host cell, the viral glycoproteins are retained on the cell surface and since they are antigenic the cell becomes a target for immune response
Antibody Mediated Penetration
- Virus enters the macrophage by attachment of its spike proteins to the CD13 receptor
- Antibodies against spike protein cannot clear the virus from the host - antibodies bind to spike proteins and facilitate entry of virus into host cell through IgG-Fcy receptor
Replication of single stranded DNA
- (+)ssDNA Strand → DNA-Dependent DNA Polymerase → dsDNA Intermediate
- (-)dsDNA Intermediate → DNA Dependent RNA Polymerase → (+) mRNA → Viral Protein
- (-) dsDNA Intermediate → DNA-Dependent DNA Polymerase → (+)ssDNA → Viral Genome
Enveloped virions release progeny virions by
Budding
Replication of double stranded DNA with Reverse Transcriptase
- dsDNA → (+) ssRNA → RNA dependent DNA polymerase → (-)ssRNA → DNA dependent DNA polymerase → (-) dsDNA → DNA dependent RNA polymerase → (+)mRNA → Viral Protein
Enveloped viruses can penetrate the host cell by
Surface Fusion
Antibody Dependent Cell Mediated Cytotoxicity
- Antibody binds antigens on the surface of the target cell
- Fc receptors on NK cell recognize bound antibody
- Cross-linking of Fc receptors signals the NK cell to kill the target cell
- Target cell dies by apoptosis
T/F: Viruses multiply by division
False
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Viruses do not have the genetic capability to muliply by divison
Naked Virions release progeny virions by
Lysis of host cell
Uncoating
Release of viral genome in host cell
Polycistronic mRNA
mRNA that encodes several polypeptides
Some (enveloped/nonenveloped) viruses induce local permeabilization of host endosomal membrane to allow virus capsid penetration into the cytoplasm
Non Enveloped
Penetration of the virus into the host cell typically occurs by
Endocytosis
pH Dependent Fusion Proteins
- Low pH in endosome promotes fusion of envelope with endosomal membrane
- Lysis of nucleocapsid by lysosomal proteases and release of viral genome
Replication of double stranded DNA viral genome
- (-)dsDNA Strand → DNA-Dependent RNA Polymerase → (+) RNA → Viral Protein
- (+) and (-) dsDNA Strand → DNA-Dependent DNA Polymerase → dsDNA → Viral Genome
Constitutive Splicing
Every intron is spliced out and every exon is spliced in
Surface membrane fusion of enveloped viruses results in
Antibody-Dependent Cell Mediated Cytotoxicity
Assembly and Maturation can take place in
Nucleus, Cytoplasm or Plasma/Cell Membrane
Fusion of virus membrane with host endosomal membrane releases the viral genome in (enveloped/nonenveloped) viruses
Enveloped
Caps are synthesized from what sources
Host Cell Enzymes
Viral Enzymes
Cap Snatching - from host mRNA
