Viral Replication and Structure Overview

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Questions and Answers

Which RNA viruses replicate in the nucleus during certain stages of their lifecycle?

  • Retroviruses and Orthomyxoviruses (correct)
  • Picornaviruses and Flaviviruses
  • Coronaviruses and Astroviruses
  • Paramyxoviruses and Rhabdoviruses

What is the primary role of structural proteins in viral assembly?

  • To inhibit host immune responses
  • To transport viral RNA to the cell membrane
  • To assist in promoting cell division
  • To form the viral capsid and encapsidate the genome (correct)

Which group in the Baltimore Classification is characterized by replication of double-stranded DNA viruses?

  • Group 3
  • Group 1 (correct)
  • Group 2
  • Group 5

During the release of enveloped viruses, what mechanism do these viruses primarily use?

<p>Budding through the cell membrane (A)</p> Signup and view all the answers

What is a key feature of positive-sense RNA viruses during replication?

<p>They directly translate to form proteins (C)</p> Signup and view all the answers

What is the role of the host's DNA-dependent DNA polymerase in the replication of double-stranded DNA viruses?

<p>It replicates the viral genome into new viral DNA strands (B)</p> Signup and view all the answers

In what compartment does assembly of nucleocapsids generally occur for most RNA viruses?

<p>In the cytoplasm (B)</p> Signup and view all the answers

Which of the following best describes the viral replication process?

<p>It combines both protein synthesis and the copying of genetic material. (B)</p> Signup and view all the answers

Which protein allows the influenza virus to attach to host cells?

<p>Hemagglutinin (HA) (B)</p> Signup and view all the answers

What mechanism do enveloped viruses like HIV utilize to enter host cells?

<p>Direct fusion (A)</p> Signup and view all the answers

What is the primary site of nucleic acid synthesis for most DNA viruses?

<p>Nucleus (D)</p> Signup and view all the answers

What process leads to the loss of virion infectivity in viral replication?

<p>Uncoating (A)</p> Signup and view all the answers

Which of the following viruses utilizes receptor-mediated endocytosis as a method of entry?

<p>Adenovirus (D)</p> Signup and view all the answers

What is the function of the M2 ion channel in the influenza virus?

<p>Enables uncoating (D)</p> Signup and view all the answers

In the context of Baltimore classification, which type of virus does NOT replicate in the nucleus?

<p>Pox viruses (D)</p> Signup and view all the answers

Which mechanism is used by viruses to release their newly-formed virions from host cells?

<p>Budding (B)</p> Signup and view all the answers

What is the primary genetic material that RNA viruses utilize for replication?

<p>Single-stranded RNA (B)</p> Signup and view all the answers

Which step follows uncoating in the viral replication process?

<p>Synthesis (D)</p> Signup and view all the answers

What characterizes the assembly step in viral replication?

<p>New virions are formed from replicated components (B)</p> Signup and view all the answers

What does the Baltimore classification system categorize viruses by?

<p>Genetic material and replication strategy (A)</p> Signup and view all the answers

Which of the following describes a common release mechanism of viruses?

<p>Viruses are released through cell lysis or budding (B)</p> Signup and view all the answers

In the context of viral attachment, what role do viral surface proteins play?

<p>They bind to specific receptors on the host cell (D)</p> Signup and view all the answers

What is a defining feature of DNA viruses during their replication process?

<p>They can integrate into the host cell's genome (C)</p> Signup and view all the answers

Which of the following viruses is categorized as an enveloped virus?

<p>HIV (D)</p> Signup and view all the answers

Flashcards

Viral Replication Step 1

Attachment (Adsorption); the virus binds to specific receptors on the host cell.

Influenza Virus Attachment

Influenza virus uses hemagglutinin (HA) to bind to sialic acid receptors on respiratory cells.

HIV Attachment

HIV uses gp120 to bind to CD4 receptors on T-cells.

COVID-19 Attachment

COVID-19 uses spike protein to bind to ACE2 receptors on the host cell, and TMPRSS2 activates that protein.

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Viral Replication Step 2

Penetration (Entry); the virus enters the host cell.

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Direct Fusion (Enveloped Viruses)

Viral envelope fuses with the host cell membrane, releasing the nucleocapsid.

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Receptor-mediated Endocytosis

The host cell membrane forms a vesicle to engulf the virus.

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Viral Replication Step 3

Uncoating; the viral capsid is removed to release the viral genome.

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Uncoating Mechanisms

Lysosomal enzymes or pH changes can cause the removal of the protective capsid.

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Viral Replication Step 4

Synthesis (Replication and Protein Production); the virus makes more copies of itself and its proteins.

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Viral Structure

Viruses contain genetic material (DNA or RNA), a protein coat (capsid), and sometimes an envelope derived from the host cell.

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Viral Replication Steps

Viral replication includes attachment, penetration, uncoating, synthesis, assembly, and release.

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Viral Attachment

Viral surface proteins bind to specific receptors on the host cell's surface, determining the virus's host range and cell type.

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Host Range

The range of host cells a virus can infect.

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Tissue Tropism

The preference of a virus for infecting particular cell types within a host.

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Viral Receptors

Specific proteins or carbohydrates on host cell surfaces that viruses bind to for infection.

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RNA Virus Replication Location

Most RNA viruses replicate in the cytoplasm of the host cell, except orthomyxoviruses and retroviruses, which replicate in the nucleus for certain stages.

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Viral Replication Steps - Assembly

Assembly of viral genome and proteins into new virions, typically occurs in the same cellular compartment where the viral nucleic acid replication happens. E.g., cytoplasm for RNA viruses, nucleus for DNA viruses.

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Viral Replication - Release

The release of new viruses from the host cell. Enveloped viruses acquire their membranes as they bud from the cell membrane.

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Negative-Sense RNA

A type of RNA virus that uses a negative-sense RNA strand as a template to make mRNA to build proteins.

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Positive-Sense RNA

A type of RNA virus that utilizes a positive-sense RNA strand directly as mRNA for protein production.

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dsDNA Virus Replication

Double-stranded DNA viruses use the host cell's DNA polymerase enzymes to replicate their DNA and transcribe their genome into mRNA, which occurs in the nucleus.

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ssDNA Virus Replication

Single-stranded DNA viruses use host DNA-dependent DNA polymerase to create a complementary strand, thus becoming a template for viral protein and genome replication—also in the nucleus.

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Baltimore Classification

A system for classifying viruses based on their genome structure and the mechanism they use for mRNA synthesis.

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Study Notes

Viral Replication Overview

  • Viral replication is a complex process encompassing multiple steps
  • The fundamental steps of viral replication are: attachment (adsorption), penetration (entry), uncoating, synthesis (replication & protein production), assembly (maturation), and release (egress).

Basic Structure of Viruses

  • Components: genetic material (DNA or RNA, but not both), protein coat (capsid), envelope (some viruses), shapes and sizes (helical, icosahedral, complex).
  • Examples of enveloped viruses: HIV, influenza virus; examples of non-enveloped viruses: adenovirus, poliovirus.

Viral Classification

  • Based on genetic material: DNA viruses, RNA viruses.
  • Based on replication strategy: different classifications exist (Baltimore Classification).

Viral Replication Steps: Step 1 - Attachment (Adsorption)

  • Mechanism: viral surface proteins bind to specific receptors on the host cell membrane.
  • Receptors are proteins, carbohydrates, or parts of the lipid bilayer.
  • Specificity: determines host range and tissue tropism (which cells the virus can infect).
  • Examples: HIV's gp120 binds to CD4 receptors; influenza virus' hemagglutinin binds to sialic acid.

Viral Replication Steps: Step 2 - Penetration (Entry)

  • Mechanisms: direct fusion (enveloped viruses); receptor-mediated endocytosis (enveloped and non-enveloped viruses).
  • Direct fusion: viral envelope merges with the host cell membrane.
  • Receptor-mediated endocytosis: cell membrane invaginates to engulf the virus.

Viral Replication Steps: Step 3 - Uncoating

  • Definition: separation of the capsid from the viral genome, resulting in loss of infectivity.
  • Mechanisms: lysosomal enzymes (degrade capsid proteins) and conformational changes (triggered by pH shifts).
  • Example: influenza virus' uncoating facilitated by M2 ion channel.

Viral Replication Steps: Step 4 - Synthesis: Replication and Protein Production

  • Viral nucleic acid synthesis begins after uncoating.
  • Location varies: most DNA viruses replicate in the nucleus, except Pox and Herpes viruses which replicate in cytoplasm. All RNA viruses replicate in the cytoplasm, except Orthomyxoviruses and retroviruses, which use nucleus at certain stages.

Viral Replication Steps: Step 5 - Assembly (Maturation)

  • Process: assembly of viral genome and proteins into new virions.
  • Locations: nucleocapsid assembly generally in the cytoplasm (for RNA viruses) or nucleus (for DNA viruses).

Viral Replication Steps: Step 6 - Release

  • Process: cell breaks open to release the virus.
  • Enveloped viruses: acquire their envelope by budding through the cell membrane.

Negative vs. Positive Sense Strand of DNA and RNA

  • Negative strand DNA/RNA must be copied (transcribed/reverse transcribed) into a complementary form (plus strand), before mRNA synthesis can start.
  • Positive strand DNA/RNA can be used directly as mRNA.

Baltimore Classification

  • A system for classifying viruses based on their genetic material, and how mRNA is made.
  • Different groups (1-7) have various genetic material and steps of synthesis. Each virus group replicates slightly differently.

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