BSR 1.04 Viral Invasion of Host Cells

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Questions and Answers

What drives the collision of virions and host cells during the initiation of infection?

Magnetic attraction

Thermal expansion

Chemical reactions

Brownian motion (correct)

Which group of viruses includes Retroviruses such as HIV?

ssRNA-RT viruses (correct)

dsRNA viruses

ssDNA viruses

dsDNA viruses

What is one of the major steps in a virus finding the right host cell?

Using lytic enzymes

Replicating its genetic material

Entering the nucleus of the cell

Adhering to the cell surface via electrostatic interaction (correct)

Which statement is true regarding the specificity of infection by viruses?

Not all cells can be infected by a virus. (B) Signup and view all the answers

What is the role of receptor molecules on the surface of host cells in virus infection?

To facilitate attachment of viruses (B) Signup and view all the answers

How are DNA viruses typically transcribed during their infection process?

Into RNA intermediate (D) Signup and view all the answers

Which statement describes virions during the initial stages of infection?

They are inanimate particles. (A) Signup and view all the answers

What type of interaction aids in the viruses’ collision with host cells?

Electrostatic interaction (C) Signup and view all the answers

What is the role of TMPRSS2 and Cathepsin B/L in the process of viral infection?

They cleave the fusion peptide to initiate infection. (C) Signup and view all the answers

What occurs to the receptor binding domain (RBD) during infection?

It undergoes a down to up configuration change. (A) Signup and view all the answers

Which of the following statements is true regarding the fusion peptide?

It is cleaved by protease enzymes during infection. (B) Signup and view all the answers

Why is the receptor binding domain (RBD) considered a target for neutralizing antibodies?

It is one of the immunogenic proteins associated with the virus. (A) Signup and view all the answers

Which enzymes are primarily responsible for exposing the receptor binding domain (RBD)?

TMPRSS2 and Cathepsins (B) Signup and view all the answers

What is the role of high affinity receptors in viral infection?

They enable viral entry into the host cells. (C) Signup and view all the answers

How do disruptions in receptor genes affect viral infections?

They block viral infection. (B) Signup and view all the answers

Which statement about accessory receptors is true?

They can accelerate the rate of viral uptake. (C) Signup and view all the answers

What happens when a cell fails to express the appropriate receptor for a virus?

It cannot be infected by the virus. (B) Signup and view all the answers

What is a key factor in the reason why some viruses infect specific cell types?

The expression of the appropriate receptor. (B) Signup and view all the answers

Why might avian influenza someday affect humans?

Mutations may lead to new modes of infection. (D) Signup and view all the answers

What is the function of neuraminidase in viral infections?

It cleaves sialic acid from galactose to facilitate infection. (A) Signup and view all the answers

Which of the following best describes the role of receptor genes in viral infections?

They confer susceptibility or resistance to viruses. (C) Signup and view all the answers

What role do fibrous stems play in the viral fusion process?

They bind to the host cell membrane. (D) Signup and view all the answers

What occurs after the virus binds to the receptor on the target cell?

Endocytosis is initiated, leading to endosome formation. (B) Signup and view all the answers

What triggers the conformational change in HA during the viral fusion of influenza virus?

Changes in pH within the endosome. (B) Signup and view all the answers

What is the purpose of pumping H+ ions into the endosome?

To create an acidic environment for fusion. (D) Signup and view all the answers

What happens to the viral and host cell membranes during fusion?

They shift configuration to pull each other closer. (C) Signup and view all the answers

What occurs following the formation of an endosome during the viral entry process?

The portal between the host cell and the virus is formed. (C) Signup and view all the answers

How are globular heads relevant to the viral fusion process?

They have been cleaved and removed prior to fusion. (B) Signup and view all the answers

What is the primary outcome of the conformational change in HA during influenza viral fusion?

Enabling fusion between the virus and the host cell membrane. (D) Signup and view all the answers

What is the primary effect of the endosome formation on the dengue virus?

It lowers the pH of the inner environment. (D) Signup and view all the answers

How does the dengue virus adapt during endosome formation?

It changes to spike-like structures that can penetrate membranes. (D) Signup and view all the answers

What occurs to the viral RNA after the capsid is released into the cytoplasm?

It travels to the rough endoplasmic reticulum. (D) Signup and view all the answers

What characteristic does the viral RNA possess that allows it to be translated into proteins directly?

It is a positive sense strand. (A) Signup and view all the answers

Which structure binds to initiate the translation of the viral RNA?

Ribosomal subunits. (A) Signup and view all the answers

What is the result of the translation of the whole viral genome?

Formation of a single long polyprotein chain. (D) Signup and view all the answers

Where are the capsid proteins located after translation?

On the cytoplasmic side of the endoplasmic reticulum. (C) Signup and view all the answers

What differentiates the location of the envelope and membrane proteins from the capsid protein?

They exist in the lumen side of the endoplasmic reticulum. (A) Signup and view all the answers

Study Notes

Initiation of Infection

Viruses initiate infection by colliding with host cells, a process influenced by Brownian motion, diffusion laws, and electrostatic interactions.
DNA viruses can be transcribed to RNA intermediates, which can then be reverse transcribed back to DNA.

Finding the Right Cell

Viruses exhibit specificity of infection; not all cells can be targeted.
Major steps for viruses to find the correct host cell:
- Adhere to cell surface through electrostatic interactions.
- Attach to specific receptor molecules once in proximity to the cell membrane; multiple receptors may be involved.
Disruption of receptor gene blocks viral infection, explaining susceptibility variations across different cell types.

Replication Cycle of Viruses

Viral attachment involves accessory receptors for low-affinity binding, which may facilitate penetration but are not essential for entry.
High-affinity receptors are crucial for viral entry; cells lacking appropriate receptors cannot be infected.

Viral Fusion Mechanism

Fusion peptide undergoes configuration changes when activated by TMPRSS2 and Cathepsin B/L proteases.
The receptor-binding domain (RBD) configuration shifts, exposing the binding site, initiating viral infection through ACE2 enzyme interaction.

Viral Entry Process (Influenza Virus)

Virus approaches a target cell and binds via the hemagglutinin (HA) to the receptor.
Endocytosis occurs, leading to endosome formation and a decrease in pH, causing conformational changes in HA.
Acidic endosome environment allows the viral capsid to release its genetic material into the cytoplasm.

Dengue Virus Infection

Aedes aegypti mosquitoes are the primary carriers of the dengue virus.
The viral RNA is a positive-sense strand that gets directly translated into proteins by the ribosomes in the rough endoplasmic reticulum.
Viral genome is expressed as a polyprotein chain, which has to be processed into functional proteins.

Important Notes

Receptor mutations can lead to new modes of infection, demonstrating the dynamic nature of viral adaptability (example: avian influenza).
Configuration changes during fusion can promote the infectious process, indicating the importance of structural adaptations in viral success.

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Description

This quiz covers the process of viral invasion of host cells, focusing on the critical initial phase of infection. It discusses how viruses collide with host cells to initiate infection, highlighting the mechanisms involved in this stage. Understanding these concepts is essential for studying virology and infectious diseases.