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Questions and Answers
What is the primary purpose of virus replication?
What is the primary purpose of virus replication?
- To create new, infectious virions (correct)
- To eliminate host cell functions
- To enhance viral protein stability
- To integrate into the host genome
In which stage of the virus replication cycle does the capsid break down?
In which stage of the virus replication cycle does the capsid break down?
- Release
- Uncoating (correct)
- Attachment
- Penetration
Which of the following statements about virus assembly is correct?
Which of the following statements about virus assembly is correct?
- Virions are replicated through cell division
- Virion assembly occurs only after maturation
- Virion assembly always requires a host cell nucleus
- Virions are assembled de novo from components (correct)
What role do co-receptors play in the virus attachment process?
What role do co-receptors play in the virus attachment process?
Which of the following stages is NOT required by all viruses in the replication cycle?
Which of the following stages is NOT required by all viruses in the replication cycle?
What determines the tropism of a virus?
What determines the tropism of a virus?
Which method is used by enveloped viruses to enter host cells?
Which method is used by enveloped viruses to enter host cells?
Why are transgenic mice expressing CD155 important for studying poliovirus?
Why are transgenic mice expressing CD155 important for studying poliovirus?
What is a key characteristic of viruses that can undergo cell-cell membrane fusion?
What is a key characteristic of viruses that can undergo cell-cell membrane fusion?
What hinders the effectiveness of vaccines against certain viruses like HIV?
What hinders the effectiveness of vaccines against certain viruses like HIV?
What is the primary function of uncoating in the virus replication cycle?
What is the primary function of uncoating in the virus replication cycle?
Which type of viruses must transport their genomes into the nucleus?
Which type of viruses must transport their genomes into the nucleus?
Which genome type typically requires RNA polymerases for gene transcription?
Which genome type typically requires RNA polymerases for gene transcription?
Which of the following viral genomes does NOT require entry into the nucleus for replication?
Which of the following viral genomes does NOT require entry into the nucleus for replication?
What replication strategy does the viral genome follow?
What replication strategy does the viral genome follow?
What distinguishes dsRNA viruses from RNA viruses that reverse transcribe?
What distinguishes dsRNA viruses from RNA viruses that reverse transcribe?
Which of the following statements is true regarding parvoviruses?
Which of the following statements is true regarding parvoviruses?
What type of genomes can viral genomes possess?
What type of genomes can viral genomes possess?
How do RNA viruses cope with monocistronic mRNA limitations?
How do RNA viruses cope with monocistronic mRNA limitations?
What is the primary function of an internal ribosome entry site (IRES) in RNA viruses?
What is the primary function of an internal ribosome entry site (IRES) in RNA viruses?
Why are RNA viruses more prone to mutations compared to DNA viruses?
Why are RNA viruses more prone to mutations compared to DNA viruses?
What is the role of scaffolding proteins during the assembly of RNA viruses?
What is the role of scaffolding proteins during the assembly of RNA viruses?
Which of the following statements correctly describes the packaging signal in RNA viruses?
Which of the following statements correctly describes the packaging signal in RNA viruses?
During which stage of the viral replication cycle does the maturation of the virus occur?
During which stage of the viral replication cycle does the maturation of the virus occur?
What distinguishes the mutation rates of RNA viruses from those of DNA viruses?
What distinguishes the mutation rates of RNA viruses from those of DNA viruses?
What is the role of reverse transcriptase in retroviruses?
What is the role of reverse transcriptase in retroviruses?
What is the role of the viral protease in the maturation of HIV?
What is the role of the viral protease in the maturation of HIV?
What is the primary process by which enveloped viruses escape from an infected cell?
What is the primary process by which enveloped viruses escape from an infected cell?
In the context of virus replication, what does the term 'eclipse period' refer to?
In the context of virus replication, what does the term 'eclipse period' refer to?
What is the burst size in a virus growth curve?
What is the burst size in a virus growth curve?
Which characteristic is typically true regarding defective viral particles?
Which characteristic is typically true regarding defective viral particles?
How does lysis of a cell differ from budding in the context of viral release?
How does lysis of a cell differ from budding in the context of viral release?
What does the multiplicity of infection (MOI) indicate?
What does the multiplicity of infection (MOI) indicate?
Which factor is essential for the curving of membranes in enveloped virus release?
Which factor is essential for the curving of membranes in enveloped virus release?
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Study Notes
Virus Infection and Replication
- Virus must replicate to create new virions for continued infection.
- Replication involves breaking down the virion capsid, releasing the genome, and assembling new particles.
- Virions assemble de novo, unlike the process in cell division.
Virus Replication Cycle
- Involves seven stages: attachment, penetration, uncoating, replication, assembly, maturation (some viruses), and release.
- These stages may not occur in a strict order.
Attachment
- Involves viral binding to host cell at the plasma membrane through specific receptors.
- Some viruses, like HIV, require co-receptors for effective binding.
- Virus attachment specificity influences the tropism (host range) of the virus.
- Example: Poliovirus requires CD155 for infection; transgenic mice expressing CD155 can be infected.
Penetration
- The virus crosses the plasma membrane using various methods.
- Enveloped viruses typically enter through membrane fusion; some also employ cell-to-cell transmission.
- Vaccine challenges arise as viruses can evade antibodies when hidden inside cells.
Uncoating
- Release of the viral genome via capsid breakdown occurs through various mechanisms.
- Some viruses transport their genomes into the nucleus, often at the nuclear envelope.
Replication
- Viral genome replication varies by nucleic acid type (DNA or RNA).
- Genome categorization: dsDNA, ssDNA, dsRNA, +ssRNA, -ssRNA, and retroviruses.
- DNA viruses usually enter the nucleus to utilize host machinery, except poxviruses, which replicate in the cytoplasm.
- RNA viruses utilize strategies like polyproteins and Internal Ribosome Entry Sites (IRES) for protein synthesis.
- RNA viruses have higher mutation rates than DNA viruses due to the lack of proofreading capability in RNA-dependent RNA polymerases.
Assembly and Maturation
- Assembly involves the formation of a mature virion around scaffolding proteins and viral DNA.
- Maturation includes proteolytic cleavage of viral proteins, necessary for virion infectiousness.
- Example: HIV Gag polyprotein is cleaved post-release to form an infectious particle.
Release
- Nascent virions escape the infected cell, typically through budding for enveloped viruses.
- Budding involves viral protein interactions with cellular membranes, forming the viral envelope.
- Non-enveloped viruses generally exit via cell lysis.
Virus Growth Curves
- One-step growth curves track the replication cycle parameters.
- Multiplicity of Infection (MOI) defines the number of viral particles per cell.
- Key phases include the eclipse period (no released particles) and latent period (time with no infectious release).
- Burst size indicates the total number of virions released from each cell.
Defective Viral Particles
- The ratio of non-infectious to infectious particles is typically higher than 10, indicating many released particles are non-infectious (defective).
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