Viral Infection Mechanisms Quiz

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Questions and Answers

A cell that has the capacity to replicate a virus but may or may not be susceptible is best described as what?

Semipermissive

Restrictive

Susceptible

Permissive (correct)

What outcome is expected with a cell that is susceptible but not permissive to a specific virus?

Abortive infection (correct)

Productive infection

Latent infection

Restrictive infection

During which phase of a viral infection can infectious virus particles not be recovered from the cell?

Productive phase

Attachment phase

Replication phase

Eclipse phase (correct)

What is the primary initial event that results in contact between the virion and the host cell?

Random collisions Signup and view all the answers

What is the function of viral anti-receptors in the infection process?

To bind to the host cell receptors Signup and view all the answers

What role does a co-receptor play in viral entry?

It is as important as receptors for viral entry Signup and view all the answers

If a virus infects a cell that is both susceptible and permissive, but the viral genome remains silent with potential reactivation, the infection is classified as what?

Latent Signup and view all the answers

What determines a virus' host range and tissue tropism?

The binding of viral anti-receptors to cellular receptors Signup and view all the answers

During viral entry, how do non-enveloped viruses typically cross the host cell's plasma membrane?

Via pore-mediated penetration or receptor-mediated endocytosis. Signup and view all the answers

What is the primary function of the uncoating process in viral replication?

To release the viral genome from the capsid. Signup and view all the answers

During viral macromolecular synthesis, from where do viruses derive necessary components and energy?

From the host cell, which supplies energy, precursors, and machinery. Signup and view all the answers

What best describes the viral assembly process?

Capsid proteins assemble, and then can enclose the genome. Signup and view all the answers

Which of the following accurately describes how enveloped viruses typically acquire their membrane?

They acquire it by budding through host cellular membranes. Signup and view all the answers

What is the fate of an infected cell when a virus escapes through cytolysis?

It is destroyed due to the virus release. Signup and view all the answers

Which step in viral replication immediately follows penetration of the host cell?

Uncoating of the viral genome Signup and view all the answers

Which step in viral replication typically uses host ribosomes?

Macromolecular synthesis Signup and view all the answers

What is the primary characteristic that defines viruses as obligate intracellular parasites?

Their reliance on host cells for energy, substrates, and replication processes. Signup and view all the answers

Which type of microscope is typically used to observe the surface details of a virus?

Scanning electron microscope (SEM). Signup and view all the answers

What are the essential components that make up a virion?

A nucleic acid genome, a capsid, and sometimes an envelope. Signup and view all the answers

What is the defining characteristic of viruses with a segmented genome?

Their genome is divided into multiple separate pieces. Signup and view all the answers

What role does RNA-dependent RNA polymerase play in viral replication?

It synthesizes RNA from an RNA template. Signup and view all the answers

Which of the following describes the assembly of a viral capsid?

Subunits associate into protomers, capsomers, and then capsid. Signup and view all the answers

What is the primary origin of the lipid component of a viral envelope?

It is obtained from the membrane of the host cell. Signup and view all the answers

What is the space between the inner face of the envelope and the nucleocapsid of a virus called?

The tegument or matrix. Signup and view all the answers

What is the term for any detectable change in a host cell caused by a viral infection?

Cytopathic effect (CPE) Signup and view all the answers

Which of the following is NOT a typical cytopathic effect (CPE) observed in infected cells?

Increased cell division Signup and view all the answers

What is the primary reason viruses require host cells for replication?

Viruses are obligate intracellular parasites. Signup and view all the answers

Which of the following methods is most commonly used for virus isolation in clinical laboratories?

Tissue culture cells Signup and view all the answers

What essential component is supplied by FBS (Fetal Bovine Serum) in tissue culture media?

Growth promoting factors Signup and view all the answers

What is the function of antibiotics in cell culture media?

To prevent bacterial contamination Signup and view all the answers

What is the primary reason given for primary cell cultures having a limited lifespan?

Contact inhibition and senescence Signup and view all the answers

What enzymes are commonly used to dissociate animal organs into single cells for primary cell cultures?

Trypsin and collagenase Signup and view all the answers

What is a key characteristic of primary cell cultures in comparison to secondary cell cultures?

They are labor-intensive and time-consuming to obtain. Signup and view all the answers

Which type of cell culture is often capable of indefinite subculturing?

Continuous cell lines Signup and view all the answers

Which method for diagnosing viral infections is identified as both slow and labor-intensive?

Culture-based systems Signup and view all the answers

Which diagnostic method is limited by its lack of sensitivity and high cost?

Electron microscopy Signup and view all the answers

What is a key advantage of using molecular methods, such as PCR, for diagnosing viral infections?

They involve the detection of viral nucleic acids. Signup and view all the answers

How do most antiviral drugs primarily function, according to the text?

By targeting viral enzymes or structures essential for replication. Signup and view all the answers

Why do antiviral drugs tend to have a narrow spectrum of activity?

They are usually specific to certain viral enzymes or structures. Signup and view all the answers

What is a significant challenge in antiviral drug development due to the nature of viruses?

Their high mutation rate and the long-term treatment required Signup and view all the answers

Which antiviral drug inhibits the fusion between the plasma membrane and the herpes simplex virus envelope?

Docosanol Signup and view all the answers

What is the primary mechanism of action of amantadine and rimantadine?

Blocking the influx of H+ through the M2 proton channel Signup and view all the answers

How do nucleoside analogs primarily function as antiviral agents?

By being incorporated into the viral genome leading to chain termination Signup and view all the answers

Which class of antiviral drugs targets HIV proteases?

Protease inhibitors Signup and view all the answers

What is the function of zanamivir and oseltamivir?

They prevent the release of new viral particles from infected cells. Signup and view all the answers

What is the primary role of interferons (IFNs) in the defense against viral infections?

They act as an 'early warning system', inducing an antiviral state Signup and view all the answers

Which viral life cycle stage is targeted by docosanol?

Viral attachment and entry Signup and view all the answers

Which of the following describes the action of nucleoside analogs?

Become incorporated into viral genome causing errors in replication Signup and view all the answers

Study Notes

General Characteristics of Viruses

Viruses are obligate intracellular parasites
They lack the capacity to produce energy, substrates, or proteins independently of a host cell
Viruses replicate their genome within the host cell
Viruses are very small, typically less than 300 nanometers in size

Viral Structure

The virion (viral particle) consists of a nucleic acid (DNA or RNA, but not both), a protein coat (capsid), and sometimes an envelope (a membrane)
A capsid is a rigid protein structure formed from subunits (protomers) assembled into capsomers
Helical and polyhedral capsids are the most common types
The envelope is an external coating to the capsid composed of lipids and glycoproteins; deriving from host cell membranes.

Viral Replication

The viral replication cycle depends on the host cell, which supplies substrates, energy, and machinery for viral protein synthesis and genome replication
Susceptible cells have functional receptors for a specific virus, leading to a possible infection
Permissive cells not only have these receptors but also can support all steps crucial to the viral replication process
If cells are susceptible and permissive, the infection is productive
Abortive infection occurs when cells are susceptible but not permissive for viral replication
Restrictive infection occurs in semipermissive cells, where viral replication is inefficient
Latent infection involves the viral genome persisting silently within the host cell, with possible reactivation later

Steps in Viral Replication

Recognition and attachment to the target cell is the initial contact
Penetration involves crossing the plasma membrane. Non-enveloped viruses may enter directly, while enveloped viruses may fuse with the host membrane or undergo endocytosis
Uncoating releases the viral genome from its protective capsid
Macromolecular synthesis of viral components occurs using host and viral enzymes
Assembly involves the synthesis of viral components to form a new viral particle
Release from the host cell using lysis (non-enveloped) or budding (enveloped)

Viral Cultures

Viruses require a host cell for replication
Embryonated eggs, experimental animals, and tissue culture cells are used to grow viruses for research or vaccines
Tissue culture cells are the primary method for isolating viruses for lab use.
Primary cell cultures are derived from specific animal tissue and have a finite lifespan.
Secondary cell cultures are formed from primary cells and may have a longer lifespan.

Diagnosis of Viral Infection

Tissue culture systems
Electron microscopy (EM)
Molecular methods (PCR, serology)

Antiviral Drugs

Antiviral drugs target viral enzymes or structures
Some antiviral drugs even stimulate host immune responses
Drugs vary according to the stage in the viral replication cycle they affect
Examples include nucleoside and nucleotide analogues, protease inhibitors, and inhibitors of viral entry or release

Interferons (IFNs)

IFNs are signaling proteins that play a role in the host's defense against viruses
They are among the body's first responses to viral infection
IFNs cause antiviral states, leading to inhibition of virus replication and protein synthesis.

Host Defenses against Viral Infection

The immune system plays an important role in fighting viral infections
The antiviral immune response consists of both innate and adaptive phases
Innate immunity involves the early, nonspecific response of various immune mechanisms, such as interferon signalling and cell killing
Adaptive immunity involves specific mechanisms in response to a virus, using antibodies for long-term protection.

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Description

Test your knowledge on viral infection processes with this quiz. Explore key concepts such as the distinction between susceptible and permissive cells, viral entry mechanisms, and the role of viral receptors. Dive into the intricate biology of viruses and their interactions with host cells.