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Questions and Answers
During viral replication, how do viruses ensure they use the host cell's machinery for their protein synthesis, while minimizing competition with the host's own mRNA?
During viral replication, how do viruses ensure they use the host cell's machinery for their protein synthesis, while minimizing competition with the host's own mRNA?
- Viruses utilize specific start codons not recognized by the host's ribosomes.
- Viruses modify their mRNA to mimic host mRNA, but with enhanced translational efficiency.
- Viruses degrade all of the host cell's mRNA upon entry.
- Viruses produce mRNA with a high affinity for host ribosomes, outcompeting host mRNA. (correct)
Some viruses can infect a cell without causing immediate lysis or cell death. What is a key characteristic that allows these viruses to establish persistent infections?
Some viruses can infect a cell without causing immediate lysis or cell death. What is a key characteristic that allows these viruses to establish persistent infections?
- The presence of a highly effective viral defense mechanism against host immune responses.
- The production of a modified cell surface receptor that prevents further viral entry.
- The ability to integrate their genome into the host cell's DNA. (correct)
- The capability to replicate exclusively within the cytoplasm, avoiding nuclear detection.
How do viruses with segmented genomes leverage this feature to increase their adaptability and evasion of host immune responses?
How do viruses with segmented genomes leverage this feature to increase their adaptability and evasion of host immune responses?
- They can efficiently repair mutations by using segments as templates, maintaining genetic stability.
- They can undergo reassortment, creating novel combinations of genomic segments during co-infection. (correct)
- They can increase the rate of transcription and translation by utilizing multiple segments simultaneously.
- They can regulate gene expression by selectively activating or silencing different segments.
In the context of viral tropism, what best describes the molecular mechanism determining a virus's capacity to infect specific cell types?
In the context of viral tropism, what best describes the molecular mechanism determining a virus's capacity to infect specific cell types?
Enveloped viruses utilize mechanisms to fuse with the host cell membrane. How does the pH influence the fusion process of some enveloped viruses entering through endocytosis?
Enveloped viruses utilize mechanisms to fuse with the host cell membrane. How does the pH influence the fusion process of some enveloped viruses entering through endocytosis?
Certain viruses are able to manipulate the host cell's actin cytoskeleton. What advantage does remodeling the actin cytoskeleton provide to a virus during its replication cycle?
Certain viruses are able to manipulate the host cell's actin cytoskeleton. What advantage does remodeling the actin cytoskeleton provide to a virus during its replication cycle?
Reverse transcriptase is crucial for retroviral replication. What is a significant challenge associated with reverse transcriptase that contributes to retroviral evolution?
Reverse transcriptase is crucial for retroviral replication. What is a significant challenge associated with reverse transcriptase that contributes to retroviral evolution?
How does the glycosylation of viral envelope proteins contribute to a virus's ability to evade the host immune system?
How does the glycosylation of viral envelope proteins contribute to a virus's ability to evade the host immune system?
During viral assembly, what determines the precise and ordered packaging of the viral genome into the capsid?
During viral assembly, what determines the precise and ordered packaging of the viral genome into the capsid?
Viruses are obligate intracellular parasites. What accounts for their reliance on a host cell for replication?
Viruses are obligate intracellular parasites. What accounts for their reliance on a host cell for replication?
What is the critical distinction between a 'susceptible' cell and a 'permissive' cell in the context of viral infection?
What is the critical distinction between a 'susceptible' cell and a 'permissive' cell in the context of viral infection?
In the viral replication cycle, what determines the tissue or organ specificity (tropism) of a virus?
In the viral replication cycle, what determines the tissue or organ specificity (tropism) of a virus?
How does the Baltimore classification system categorize viruses, and what is the primary basis of this categorization?
How does the Baltimore classification system categorize viruses, and what is the primary basis of this categorization?
What is a key function of viral nucleic acid polymerases, such as reverse transcriptase, that are integral to their replication strategies?
What is a key function of viral nucleic acid polymerases, such as reverse transcriptase, that are integral to their replication strategies?
Non-enveloped viruses must breach the host cell membrane to deliver their genome. By what mechanism do some non-enveloped viruses accomplish entry into the host cell?
Non-enveloped viruses must breach the host cell membrane to deliver their genome. By what mechanism do some non-enveloped viruses accomplish entry into the host cell?
Enveloped viruses can enter host cells either by fusion with the plasma membrane or via endocytosis. For viruses that enter via endocytosis, what triggers the fusion event necessary for viral genome release?
Enveloped viruses can enter host cells either by fusion with the plasma membrane or via endocytosis. For viruses that enter via endocytosis, what triggers the fusion event necessary for viral genome release?
After a virus has successfully entered a host cell, how can it ensure that the host cell's ribosomes preferentially translate viral mRNA rather than cellular mRNA?
After a virus has successfully entered a host cell, how can it ensure that the host cell's ribosomes preferentially translate viral mRNA rather than cellular mRNA?
What is the significance of RNA-dependent RNA polymerases in the replication cycle of certain viruses, and in which virus families are they typically found?
What is the significance of RNA-dependent RNA polymerases in the replication cycle of certain viruses, and in which virus families are they typically found?
How do viruses with a ssDNA genome (Group II in the Baltimore classification) replicate their genome once inside the host cell?
How do viruses with a ssDNA genome (Group II in the Baltimore classification) replicate their genome once inside the host cell?
In the context of viral mRNA synthesis, what is a unique aspect of poxviruses compared to other DNA viruses?
In the context of viral mRNA synthesis, what is a unique aspect of poxviruses compared to other DNA viruses?
How do segmented viruses, such as influenza virus, achieve genetic diversity through antigenic shift, and what enzyme facilitates this process?
How do segmented viruses, such as influenza virus, achieve genetic diversity through antigenic shift, and what enzyme facilitates this process?
What role do matrix proteins play in the assembly and budding of enveloped viruses?
What role do matrix proteins play in the assembly and budding of enveloped viruses?
What is the significance of sialic acid as a receptor for influenza viruses, and how does the structure (α2,6 vs. α2,3) influence host specificity?
What is the significance of sialic acid as a receptor for influenza viruses, and how does the structure (α2,6 vs. α2,3) influence host specificity?
What is the role of the enzyme integrase in the replication cycle of retroviruses, and at what stage of the replication cycle does it act?
What is the role of the enzyme integrase in the replication cycle of retroviruses, and at what stage of the replication cycle does it act?
How does the process of viral budding differ between enveloped viruses that assemble at the plasma membrane versus those that assemble at internal membranes?
How does the process of viral budding differ between enveloped viruses that assemble at the plasma membrane versus those that assemble at internal membranes?
What distinguishes the release mechanisms of enveloped versus non-enveloped viruses, and which cellular processes are associated with each?
What distinguishes the release mechanisms of enveloped versus non-enveloped viruses, and which cellular processes are associated with each?
In retroviruses, what is a provirus and what role does it play in latent infection and potential oncogenesis?
In retroviruses, what is a provirus and what role does it play in latent infection and potential oncogenesis?
What is one consequence of the error-prone nature of reverse transcriptase (RT) in retroviruses such as HIV?
What is one consequence of the error-prone nature of reverse transcriptase (RT) in retroviruses such as HIV?
Why do some viruses require the active transport of the viral genome to the nucleus, and how does this impact the replication cycle?
Why do some viruses require the active transport of the viral genome to the nucleus, and how does this impact the replication cycle?
What is the role of viral proteases, such as HIV protease, in the replication cycle, and what is the result if these proteases are inhibited?
What is the role of viral proteases, such as HIV protease, in the replication cycle, and what is the result if these proteases are inhibited?
How do some viruses, like HIV, utilize cellular transport mechanisms to facilitate their replication, and what advantages does this provide?
How do some viruses, like HIV, utilize cellular transport mechanisms to facilitate their replication, and what advantages does this provide?
Many viruses encode proteins that shut down host cell protein synthesis. How does this promote efficient viral replication?
Many viruses encode proteins that shut down host cell protein synthesis. How does this promote efficient viral replication?
What is the role of glycosylation in the life cycle of many viruses, and how do viruses co-opt these host enzymes to facilitate their pathogenicity?
What is the role of glycosylation in the life cycle of many viruses, and how do viruses co-opt these host enzymes to facilitate their pathogenicity?
During viral budding, how do viruses that bud at internal cell compartments ensure proper localization and incorporation of viral envelope glycoproteins, and what advantages does this provide?
During viral budding, how do viruses that bud at internal cell compartments ensure proper localization and incorporation of viral envelope glycoproteins, and what advantages does this provide?
The influenza A virus's hemagglutinin (HA) protein binds to sialic acid residues on host cells. How does the HA protein's binding preference influence the virus's host range, and what implications does reassortment of HA have for pandemic potential?
The influenza A virus's hemagglutinin (HA) protein binds to sialic acid residues on host cells. How does the HA protein's binding preference influence the virus's host range, and what implications does reassortment of HA have for pandemic potential?
Some viruses encode proteins that antagonize the interferon response. How does antagonizing the interferon response benefit the virus, and which part of the viral lifecycle is most impacted by this antagonism?
Some viruses encode proteins that antagonize the interferon response. How does antagonizing the interferon response benefit the virus, and which part of the viral lifecycle is most impacted by this antagonism?
What mechanism do some viruses use to exploit the host cell's ubiquitin-proteasome system (UPS) to promote viral replication, and which steps are most impacted by this?
What mechanism do some viruses use to exploit the host cell's ubiquitin-proteasome system (UPS) to promote viral replication, and which steps are most impacted by this?
Some viruses induce the formation of specialized intracellular compartments, known as viral factories or replication compartments. How do these structures benefit the replicating viruses, and what functions do they serve in increasing viral replication efficiency?
Some viruses induce the formation of specialized intracellular compartments, known as viral factories or replication compartments. How do these structures benefit the replicating viruses, and what functions do they serve in increasing viral replication efficiency?
Flashcards
Are viruses intracellular or extracellular?
Are viruses intracellular or extracellular?
Viruses are obligate intracellular parasites.
What is the point of viral replication?
What is the point of viral replication?
The production of new infectious particles (virions).
What is a susceptible cell?
What is a susceptible cell?
A cell that produces the receptor(s) required for viral entry.
WHat cell can BOTH take up a viral particle and replicate it?
WHat cell can BOTH take up a viral particle and replicate it?
A susceptible AND permissive cell is the only cell that can take up a viral particle and replicate it
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What is a resistant cell?
What is a resistant cell?
A cell that does not produce the required receptors for viral entry.
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What is a permissive cell?
What is a permissive cell?
A cell that is able to support viral replication when a viral genome is introduced.
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What are the 3 steps of viral entry?
What are the 3 steps of viral entry?
- Adhesion to cell surface (no specificity). 2. Attachment to specific receptor molecules on cell surface. 3. Transfer of the genome inside the cell.
Why is receptor usage key for a virus?
Why is receptor usage key for a virus?
Viruses have evolved to bind to receptors to exploit tissue/organ specificity of a virus.
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What mediates attachment for enveloped vs nonenveloped?
What mediates attachment for enveloped vs nonenveloped?
Non-enveloped viruses attach via capsid proteins on the virus surface, enveloped viruses attach via glycoproteins embedded in the viral membrane.
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How do cells uptake macromolecules?
How do cells uptake macromolecules?
Cells use different mechanisms for uptake of molecules from the extracellular fluid. After binding to receptors, virus particles gain entry through these mechanisms.
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What is the Baltimore classification?
What is the Baltimore classification?
Baltimore classification organizes viruses by how they store and use genetic material.
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What is a nucleic acid polymerase?
What is a nucleic acid polymerase?
An enzyme that synthesizes long chains (polymers) of nucleic acids.
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Where does synthesis occur for DNA and RNA?
Where does synthesis occur for DNA and RNA?
DNA viruses: mRNA synthesis and replication in nucleus. RNA viruses: mRNA synthesis and replication in cytoplasm.
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List the 3 different Mechanisms fo viral release:
List the 3 different Mechanisms fo viral release:
Three different mechanisms: Budding, exocytosis, and cell lysis. Enveloped viruses: budding or exocytosis. Nonenveloped viruses: lysis
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What are the most common steps in assembly?
What are the most common steps in assembly?
Formation of individual structural units, assembly of the protein shell, selective packaging of nucleic acid genome, release from host cell, acquisition of an envelope, and maturation of virus particles.
Signup and view all the flashcardsStudy Notes
- Introduction to Virology: Lecture 3 focuses on the viral replication cycle.
- Instructor: Candelaria Gonzalez Moreno, DVM, PhD (Locum).
- Source material primarily comes from "Principles of Virology" 5th ed. by Flint, Racaniello, Rall, Hatziioannou, and Skalka, "Fenner’s Veterinary Virology" 5th ed. by Maclachlan, James, Dubovi, and Edward J., and Virology Lectures 2023 Vincent Racaniello Columbia University
Virus Essentials
- Viruses are obligate intracellular parasites.
- New infectious particles (virions) are only produced within susceptible and permissive cells.
- Viral reproduction relies heavily on host cell functions, including the machinery for mRNA translation and sources of energy.
Steps in the Replication Cycle
- Attachment and entry are the first steps in the cycle.
- mRNA synthesis follows attachment and entry.
- Translation of the viral genome occurs after mRNA synthesis.
- Genome replication is a key step in producing new viruses.
- Assembly of viral components into new virions occurs after genome replication.
- Release of virions from the host cell completes the cycle.
- The division of the replication cycle into steps is somewhat artificial but facilitates study and understanding.
Definitions Related to Viral Infection
- A susceptible cell possesses the necessary receptor(s) for viral entry but may not support viral replication.
- A resistant cell lacks the required receptor(s) for the virus to enter and replicate.
- A permissive cell can support viral replication if the viral genome is introduced, regardless of susceptibility.
- Only cells that are both susceptible and permissive can be infected by a virus and replicate it.
Attachment and Entry Details
- Virus particles are too large for simple diffusion across the plasma membrane.
- Attachment and entry occurs in three steps:
- Adherence to the cell surface is the first step, without any specificity.
- Attachment to specific receptor molecules on the cell surface, with potentially multiple receptors involved.
- Transfer of the viral genome inside the cell.
- Receptors have natural cellular functions, and viruses have evolved to exploit them.
- Receptor usage determines the tissue/organ specificity (tropism) of a virus.
ACE2 Receptor
- ACE2 serves as the receptor for SARS-CoV-2.
Receptor-Binding Sites
- Non-enveloped viruses attach via viral capsid proteins using surface features like canyons and loops or protruding fibers.
- Enveloped viruses use glycoproteins incorporated into the cell-derived membranes to mediate fusion with new host cell membranes.
Salic Acid
- Salic acid is a receptor for influenza viruses.
- α(2,6) is preferentially bound by human strains and α(2,3) by avian strains.
Entry Into Host Cells
- Cells use various mechanisms to uptake macromolecules from the extracellular fluid.
- After binding to receptors, virus particles can enter cells through mechanisms.
Entry of Enveloped Viruses
- Fusion with plasma membrane or fusion with endosomal membrane.
Entry of Non-Enveloped Viruses
- Disrupting the endosomal membrane (adenovirus).
- Forming a pore in the endosomal membrane (poliovirus).
- Disrupting the lysosomal membrane (reovirus).
Viral Replication Cycle: mRNA Synthesis, Translation and Genome Replication
- Viral Genome classifcation according to Baltimore as follows:
- Group I: Positive Double-stranded DNA (dsDNA)
- Group II: Positive Single-stranded DNA (ssDNA)
- Group III: Positive Double-stranded RNA (dsRNA)
- Group IV: Positive-stranded single-stranded RNA (+ssRNA)
- Group V: Negative single-stranded RNA (-ssRNA)
- Group VI: Retroviruses
- Group VII: Pararetroviruses
DNA Genomes
- dsDNA genome replication involves synthesis of +DNA from -DNA
- ssDNA genome have + or - DNA synthesized into dsDNA
RNA Genomes
- ss (+) RNA uses a RNA template to syntheisze -DNA
- dsRNA genome has a RNA template syntehsizing mRNA but also replicatng itself
- ss (+) RNA replicating through a DNA intermediate has reverse transcription of RNA into DNA
Nucleic Acid Polymerases
- Four types:
- DNA-dependent DNA polymerase (DdDp): Synthesizes DNA from a DNA template.
- DNA-dependent RNA polymerase (DdRp): Synthesizes RNA from a DNA template.
- RNA-dependent DNA polymerase (reverse transcriptase/RT): Synthesizes DNA from an RNA template.
- RNA-dependent RNA polymerase (RdRp): Synthesizes RNA from an RNA template.
Viral Replication Cycle: Assembly and Release
- Process includes formation of structural unit from viral proteins.
- The protein shell assembles by interactions of structural units.
- Nucleic acid genome is selectively packaged with other virion componenets.
- After it is released form host cell it may aquire an envelope and start maturation or infect a new host
- Assembly can occur at internal membanes
Assembly
Assembly follows a specific sequence involving the DNA genome and the tail fiber
Acquisition of an Envelop
- Requires matrix or envelope proteins, envelope glycoproteins and capsid
- Budding can take place a the plasma membrane, ER, Golgi, or Exosomes
Release
- Budding
- Exocytosis
- Cell Lyse
Retroviruses Replication
- (+) strands of mRNA
- Surface and matrix proteins are used
- Integrase used
Learning outcomes:
- Host cells provide functions like machinery for translation and energy sources.
- The viral replication cycle includes stages such as attachment, entry, mRNA synthesis, translation, genome replication, assembly, and release.
- Susceptible cells have receptors for viral entry, resistant cells lack these receptors, and permissive cells support replication after genome entry.
- Attachment and entry require specific processes due to the size and nature of viruses.
- Attachment requires adhesion to cell surface (no specificity), attachment to specific receptor molecules on cell surface (more than one receptor type may be involved), and transfer of the genome inside the cell.
- Enveloped viruses bind receptors using glycoproteins. Non-enveloped viruses bind via their viral capsid protein
- Enveloped entry: fusion with host cell membrane or through the endosome
- Types of entry of non-enveloped viruses including disrupting the endosomal membrane or forming a pore
- Nucleic acid polymerases are DNA-dependent DNA polymerase, DNA-dependent RNA polymerase, RNA-dependent DNA polymerase, and RNA-dependent RNA polymerase.
- Viral DNA-dependent RNA-polymerase must be packaged in the virionof poxviruses
- RNA-dependent RNA-polymerases must be packaged in the virion of ss(-) RNA and dsRNA viruses
- Reverse transcriptase is used by Retroviruses and Pararetroviruses
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