Virology Quiz on Virus Structure and Function

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Questions and Answers

Which of the following accurately describes the components of the virion?

The capsid protects the nucleic acid and is typically found in helical forms. (correct)

The matrix is responsible for organizing the genome only.

Nucleocapsid consists of the capsid and enveloped nucleic acid.

The nucleic acid is always made of double-stranded RNA.

What consequence does the presence of a viral envelope have on virus infectivity?

It enhances viral attachment regardless of environmental conditions.

It decreases viral infectivity if exposed to heat or detergents. (correct)

It allows viruses to survive indefinitely in dry conditions.

It makes viruses highly resistant to chemical agents.

Which statement is true regarding RNA viruses?

They can only be double-stranded and linear.

RNA viruses do not use a nuclear matrix for assembly.

All RNA viruses have a single negative sense strand.

They may contain segmented genetic material. (correct)

How do naked viruses often aid in their transmission?

They survive extreme temperatures and remain infectious over time. Signup and view all the answers

What is a defining characteristic of complex symmetry viruses?

They lack a defined shape, differing from helical or icosahedral viruses. Signup and view all the answers

What role do viral surface glycoproteins play when embedded in an envelope?

They mediate attachment to the host cell and induce neutralizing antibodies. Signup and view all the answers

What is the primary function of the viral matrix protein?

It organizes and maintains the overall structure of the virion. Signup and view all the answers

Which characteristic is NOT true about DNA viruses?

They are always linear in structure. Signup and view all the answers

Which outcome results from the presence of a naked virus in adverse environments?

It increases the likelihood of contamination from infected surfaces. Signup and view all the answers

What distinguishes the persistence of DNA viruses compared to RNA viruses?

DNA viruses can remain chronic and latent over time. Signup and view all the answers

Which statement is true regarding the replication mechanisms of RNA viruses?

RNA viruses frequently encode their own polymerases for replication. Signup and view all the answers

What is a key feature of retroviruses that differentiates them from typical RNA viruses?

Retroviruses utilize RNA-dependent DNA polymerase to replicate. Signup and view all the answers

How do the genome structures of RNA viruses influence their mutation rates?

RNA viruses can rapidly adapt due to high mutation rates. Signup and view all the answers

Which of the following accurately describes the role of viral polymerases?

Different types of polymerases are essential for various viral replication processes. Signup and view all the answers

What distinguishes the replication process of infective viral particles from other microorganisms?

They self-assemble individual parts. Signup and view all the answers

Which component of a viral particle is responsible for protecting against environmental degradation?

Delivery system Signup and view all the answers

How do different properties of viruses influence their classification?

Characteristics such as genome structure play a key role in classification. Signup and view all the answers

What is contained within the payload of an infective viral particle?

The genome and necessary enzymes for replication Signup and view all the answers

What role do structures in the delivery system of a viral particle serve?

Bind to host target cells. Signup and view all the answers

Which of the following statements is true regarding viral transmission between hosts?

Different types of viruses can spread through unique transmission methods. Signup and view all the answers

Which characteristic is NOT typically used to classify different types of viruses?

Antibody response in the host Signup and view all the answers

Which characteristic is unique to viruses that induce syncytia formation?

Fuse directly at the cellular surface Signup and view all the answers

What is the primary location where RNA viruses typically release their genome?

Cytoplasm Signup and view all the answers

Which type of virus is an exception and delivers its genome directly to the cytoplasm?

Poxviruses Signup and view all the answers

What viral family can directly mediate fusion at the cell's surface and lead to syncytial formation?

Paramyxoviridae Signup and view all the answers

Which statement correctly describes the biosynthesis process of viruses?

Both types replicate using host cell machinery Signup and view all the answers

Which of the following viruses requires the uncoating of nucleic acid for replication?

Both DNA and RNA viruses Signup and view all the answers

In which viral classification does syncytia formation predominantly occur?

Paramyxoviridae Signup and view all the answers

Which process is essential before a DNA virus can replicate its genome?

Transport to the nucleus Signup and view all the answers

Which of the following is NOT a characteristic of the Reoviridae family?

Causes syncytia formation Signup and view all the answers

What feature distinguishes orthomyxoviruses from other RNA viruses?

Their genome resides in the nucleus Signup and view all the answers

What is the primary mode of transmission for the virus discussed?

Respiratory route Signup and view all the answers

Which factor is NOT relevant to the general order of microbial resistance against biocides?

Color of the organism Signup and view all the answers

Which viral classification criterion is considered the most consistent?

Physical and biochemical characteristics Signup and view all the answers

What type of genetic material is NEVER associated with an icosahedral, non-enveloped virus?

ssRNA Signup and view all the answers

Which of the following statements regarding viral spreading is accurate?

The virus can persist without killing the host cells. Signup and view all the answers

Which viral genome type is correctly classified under helical encapsulated viruses?

ssRNA Signup and view all the answers

Which characteristic is NOT typically used in the classification of viruses?

Color of the virus Signup and view all the answers

What statement about the gastrointestinal survival of this virus is true?

It cannot survive in the gastrointestinal tract. Signup and view all the answers

Which type of virus has a complex structure and is enveloped?

Complex, enveloped virus Signup and view all the answers

Which option best describes the characteristic of viral names?

They may reflect genetic structure or geographic origin. Signup and view all the answers

Study Notes

Introduction to Virology: Viral Structure and Replication

The presentation is on viral structure and replication, part of a medical microbiology course.
It focuses on understanding viruses, their components, replication cycles, and their impact on disease manifestation.

Learning Objectives

Students will be able to outline how viral properties classify different virus types.
Students will be able to describe viral particle components and their functions within the replication cycle.
Students will be able to describe how viral properties influence viral transmission and spread between cells and hosts.
Students will be able to compare and contrast the replication cycles of different viruses (DNA, +ss RNA, -ss RNA, dsRNA, retroviruses).
Students will be able to explain how viral and host factors affect disease manifestation.

Discovery of Viruses: Serendipity at its Fin

Iwanowski (1892) discovered that a filterable agent caused tobacco mosaic disease initially thought to be bacterial.
Stanley (1935) crystallized this agent, now known as Tobacco Mosaic Virus (TMV).
Electron microscopy revealed TMV's rod-shaped, helical structure.
Viruses are significantly smaller than bacteria and cells.

Definitions and Properties of a Virus

Viruses are non-filterable through bacteriological filters.
They are obligate intracellular parasites—they need a host cell to reproduce.
They cannot create energy or proteins independently of a host cell.
Viruses contain either DNA or RNA, but not both.
Viruses are composed of nucleic acid (DNA or RNA) encased in a protein coat called the capsid.
Naked viruses have only a capsid, while enveloped viruses have a capsid surrounded by a lipid envelope.
Viruses reproduce by assembling individual parts rather than binary fission.

Viral Structure + General Concepts

Different viral structures (e.g. helical, icosahedral, complex) are suited for particular functions and types of viruses.

What are the Different Features of Viruses?

Viral properties influence classification, enabling the development of specific classifications of viruses.
Features of viral particles and the replication cycles are vital elements in virus classification.

Schematic Diagram of an Infective Viral Particle

A viral particle's delivery system, which protects it in the environment and aids attachment to host cells, contains the genome and enzymes to initiate virus replication steps.

The Payload: DNA or RNA

DNA viruses may have single or double-stranded DNA, in linear or circular forms.
RNA viruses may have single or double-stranded RNA, in linear forms which can be segmented.

Components of the Basic Virion

The nucleocapsid encapsulates the nucleic acid (DNA or RNA).
The capsid is a protein shell encapsulating the nucleic acid; it can assemble itself.
Viruses may be naked (no envelope) or enveloped (membrane derived from host).
Enveloped viruses contain glycoproteins to enable attachment and mediate fusion to the host cell.
The viral matrix maintains virion structure.
A virion is a complete infectious virus particle.

Capsids Symmetry (Structure)

Icosahedral symmetry involves a roughly spherical capsid with many identical subunits.
Helical symmetry involves a helical arrangement of capsid units, creating a rod shape or filamentous shape.
The structure and symmetry of the capsid are crucial for classifying viruses.

Exceptions to Symmetry (Complex Symmetry Viruses)

Poxviruses (dsDNA) have complex structures
Bacteriophages have complex structures

Consequences of Naked/Non-Enveloped Capsid on Viruses

Naked viruses are more resistant to environmental factors like temperature, chemicals and dryness.
Naked viruses’ transmission is mainly through contaminated surfaces (fomites).
Naked viruses persist longer in the environment and replicate better in those conditions.

Consequences of Enveloped Capsid on Viruses

Enveloped viruses are sensitive to environmental factors like drying, heat and detergents.
Enveloped viruses’ transmission is mainly through fluids (droplets, secretions).
Host cells must deliver enveloped viruses to allow the virus to enter and propagate.

Consequences of Envelope on Viruses (Continued)

Enveloped viruses are transmitted through droplets, secretions and sometimes respiratory tract or blood.
Enveloped viruses typically cannot survive in the gastrointestinal tract and therefore transmission is via fecal-oral route less common.

General Order of Microbial Resistance against Biocides

The order of resistance to microbial agents is based on various characteristics (viral size, envelope existence).

Naming and Classification of Viruses

Viral naming often reflects their properties, associated diseases, or the location they are discovered.
Classification is based on various viral characteristics including size, morphology, genome type and replication strategy.

Type of Capsid + Genome Type

Specific categories of viruses exist according to capsid type and genome (dsDNA, ssDNA, dsRNA, +ssRNA, -ssRNA, retroviruses)

Classification: DNA Viruses of Medical Importance

DNA viruses are grouped into seven families related by their characteristics.

Classification: RNA Viruses of Medical Importance

RNA viruses are grouped into at least 14 families.

Viral Replication

Viral replication follows a general six-step process – attachment, penetration, uncoating, biosynthesis, assembly, and release.

Step 1 (Attachment/Adsorption)

Viral attachment depends on two factors: viral attachment proteins (VAPs) and cellular receptors.
VAPs on viruses and receptors on host cells ensure correct matching of viruses and susceptible cells.

Step 2: Penetration/Entry

Penetration differs based on whether a virus has an envelope.
Enveloped viruses often fuse to host cell membranes.
Non-enveloped viruses may enter through endocytosis.

How Enveloped Viruses Gain Entry into a Host Cell

Viruses attach to host cell surface receptors.
Fusion of viral envelope and host cell membrane facilitates entry.

How Non-Enveloped and Some Enveloped Viruses Enter

Non-enveloped viruses enter through endocytosis.
Some enveloped viruses also enter via endocytosis.

Fusion/Syncytium Formation in Some Viral Infections

Fusion of infected cells with neighboring cells leads to the formation of multinucleated cells called syncytia.
This is facilitated by surface expression of viral fusion proteins.
Viral fusion protein triggers membrane fusion which drives synthesis of syncytia.

Step 3: Uncoating/Release of Nucleic Acid from Capsids

DNA viruses release their genome into the nucleus.
RNA viruses release their genomes into the cytoplasm, except for orthomyxoviruses which have different uncoating mechanisms.

Step 4: Biosynthesis of Protein and Nucleic Acid (Replication)

Synthesis of viral proteins and nucleic acids leads to viral replication.
Synthesized molecules are required for viral maturation and assembly.

Differences between Viral Genome Replication

Different types of viruses have different replication strategies dependent on the type of nucleic acid.

Properties of Viruses Based on Genome

DNA viruses are generally permanent in host cells.
Replication can involve distinct events in the nucleus or cytoplasm, dependent on the type of virus.
RNA viruses are generally labile.
Replication may involve different processes in the cytoplasm, according to the type of virus.
Viral gene replication may be prone to mutations.

Viral Polymerases

RNA viruses use RNA-dependent RNA polymerases (RdRp), sometimes RNA-dependent DNA polymerases (reverse transcriptase).
DNA viruses use DNA-dependent DNA polymerases (DdDp) and DNA-dependent RNA polymerases (DdRp) for replication.

Baltimore Classification

Classifies viruses based on their method of synthesizing mRNA.

Overview of Assembly & Release

Assembling viral particles involves joining capsid proteins with replicated genomes.
Release of virions from a host cell can result from cell lysis or budding through cell membranes.

Factors Influencing Disease Manifestation

Viral factors (e.g., mode of transmission, virulence factors).
Host factors (e.g., immune response, general health).

How Some People Get Sick While Others Don't?

Viral and host factors influence disease manifestation and how the virus reacts.
Individual susceptibility and response to infection vary on several conditions and parameters.

Factors Which Influence Disease

Viral factors determine the entry site of a virus.
Host factors influence immunity and general health, which can determine whether a virus causes disease.

On Your Own

Students should draw and label a basic virion, including appropriate components for naked and enveloped viruses.

To Do (Other instructions for the students)

List the DNA and RNA virus families of medical importance.
List major virus families based on genome, capsid and envelope.
List the DNA virus families and their replication strategies.
List the RNA virus families and their replication strategies.

Alternate Views: Strategies for DNA and RNA Virus Replication

Different viruses have different approaches to replicating their genomes within host cells.
Details vary for enveloped and non-enveloped viruses.
DNA viruses usually incorporate into the host's genome, or use cellular machinery for their replication and protein synthesis.
RNA viruses frequently have their own mechanisms for replicating their genomes.
Specific strategies exist among types of viruses.

What are the Rules of Viral Replication (Location in the Cell)?

DNA viruses usually replicate in the nucleus.
RNA viruses frequently replicate in the cytoplasm, with notable exceptions.

Example: Norovirus, a Common Cause of Viral Gastroenteritis

Norovirus is a highly contagious virus that causes vomiting and diarrhea.
Norovirus is resistant to common disinfectants and persists in food and on surfaces.

Example: HIV, the Cause of Human Acquired Immunodeficiency Syndrome

HIV causes a persistent productive infection in macrophages(spreads quickly) which can last several days to weeks.
HIV infects T-cells and memory cells, influencing the immune response.
HIV utilizes the host cell for replication.

Example: Varicella-Zoster Virus (VZV), the Etiologic Agent of Chickenpox & Shingles

VZV is transmitted by respiratory droplets and causes chickenpox and shingles—a more common endogenous infection.

Additional Thought Questions

Some viruses have genomes that act as infectious nucleic acids.
Orthomyxoviruses replicate in the nuclei.
Poxviruses replicate in the cytoplasm.

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Description

Test your knowledge on the components of virions, including their structures, functions, and replication mechanisms. This quiz covers essential concepts such as viral envelopes, naked viruses, and differences between RNA and DNA viruses. Prepare to explore the fascinating world of virology!