Hepadnavirus Classification and Replication Quiz

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Questions and Answers

Which characteristic accurately describes the Baltimore classification of Hepadnaviruses?

Their mRNA is produced solely from an RNA template.

They are classified as double-stranded RNA viruses.

Their replication involves reverse transcriptase and a partial double-stranded DNA genome. (correct)

They have single-stranded RNA genomes that directly function as mRNA.

What role does reverse transcriptase play in the life cycle of Hepadnaviruses?

It converts single-stranded RNA into double-stranded RNA for replication.

It helps package the genome inside the viral capsid.

It makes DNA from the RNA genome and incorporates it into the host genome. (correct)

It transcribes mRNA directly from the double-stranded DNA template.

Which of the following statements correctly describes the mRNA production mechanism for Group VII viruses?

mRNA is produced from single-stranded DNA templates during replication.

The viral genome is single-stranded RNA that acts as a template for mRNA.

mRNA is transcribed directly from double-stranded RNA.

An RNA intermediate serves as both mRNA and template for DNA replication. (correct)

In the Baltimore classification, where do retroviruses like HIV fit?

They belong to Group VI and use reverse transcriptase to produce DNA from RNA. Signup and view all the answers

What is the initial step in the replication strategy of Hepadnaviruses?

Conversion of mRNA into single-stranded RNA intermediates. Signup and view all the answers

Which property confirms that viruses cannot replicate independently in the environment?

Obligate intracellular parasite Signup and view all the answers

What was a significant finding in the early study of Tobacco Mosaic Virus by Iwanowski?

He observed that sap remained infectious post filtration Signup and view all the answers

Which statement correctly describes the structure of viruses?

Viruses consist of either DNA or RNA, but not both Signup and view all the answers

Which of the following details about viral structure is inaccurate?

Enveloped viruses are always rod-shaped Signup and view all the answers

In the context of viral replication cycles, which characteristic differentiates retroviruses from other types of viruses?

They contain RNA that is reverse transcribed to DNA Signup and view all the answers

Which characteristic of the Tobacco Mosaic Virus was revealed through electron microscopy?

It is a helical particle Signup and view all the answers

What role do viral factors play in the disease manifestation in hosts?

They can influence the severity and type of disease symptoms Signup and view all the answers

What is the primary method through which an infective particle assembles its components?

Through self-assembly Signup and view all the answers

Which component of a viral particle functions as a delivery system?

Capsid Signup and view all the answers

What is contained within the payload of a viral particle?

The genome and replication enzymes Signup and view all the answers

How do the properties of different types of viruses influence transmission between hosts?

They govern the transmission methods and host range. Signup and view all the answers

What role does the envelope play in certain types of viral particles?

It protects the viral payload from host immune responses. Signup and view all the answers

Which of these features are crucial for classifying different viruses?

The virus's method of replication and structural makeup Signup and view all the answers

What initiates the first steps in the viral replication cycle?

Viral enzymes contained in the payload Signup and view all the answers

In the context of viral structure, which factor is essential for binding to host target cells?

Specific structures on the virus Signup and view all the answers

What is a unique characteristic of viral replication compared to cellular organisms?

Viral particles require a host cell for replication. Signup and view all the answers

Which of the following describes the transmission routes of the virus?

Spread via respiratory droplets and secretions Signup and view all the answers

What characteristic is least likely to be involved in classifying viruses?

Physical environment where the virus is typically found Signup and view all the answers

Which factor is NOT mentioned as part of the general order of microbial resistance against biocides?

Nutrient availability Signup and view all the answers

Which type of viral capsid is correctly paired with its genomic structure?

Helical, non-enveloped - ssDNA Signup and view all the answers

Which statement about viral persistence is accurate?

Viruses can be persistent without killing host cells Signup and view all the answers

What aspect is crucial for understanding how a virus replicates?

Size and structure of the virus capsid Signup and view all the answers

Which type of genome is associated with icosahedral, enveloped viruses?

+ssRNA Signup and view all the answers

Which transmission method is inaccurately attributed to the virus?

Ingesting contaminated food Signup and view all the answers

What characteristic is essential for a virus to persist in a host?

Infection without directly harming cells Signup and view all the answers

Which classification method is least relevant to virus grouping?

Means of infection Signup and view all the answers

What are the characteristics of dsDNA viruses like poxviruses?

They multiply only through cellular replication. Signup and view all the answers

How many families do RNA viruses associated with human disease belong to?

14 families Signup and view all the answers

What is the first step in the viral multiplication process?

Attachment Signup and view all the answers

What do viral attachment proteins (VAPs) do in the process of attachment?

Extend from the surface of the virion. Signup and view all the answers

How do most enveloped viruses gain entry into a host cell?

Through attachment to cell-surface receptors followed by membrane fusion. Signup and view all the answers

What factor does not influence the attachment step of viral multiplication?

The size of the virus. Signup and view all the answers

Which viral family is known to be associated with the formation of syncytium?

Herpesviridae Signup and view all the answers

What is the term for the release of nucleic acid from a virus's capsid?

Uncoating Signup and view all the answers

Which process is not involved in the assembly step of viral multiplication?

Release of viral enzymes Signup and view all the answers

What does penetration/entry depend on for viruses without an envelope?

Receptor-mediated endocytosis. Signup and view all the answers

Study Notes

Introduction to Virology: Viral Structure and Replication

This presentation introduces virology, focusing on viral structure and replication.
The presenter is Valerie E. Cadet, PhD, Assistant Dean of Health Equity Integration, and Professor of Microbiology and Immunology.

Learning Objectives

Students will be able to outline how viral properties classify different viruses.
Detail the components of a viral particle and explain the function of each component related to the viral replication cycle.
Describe how viral properties influence viral transmission between hosts and viral spread between cells in a host.
Compare and contrast the replication cycles of DNA, +ss RNA, -ss RNA, dsRNA, and retroviruses.
Clarify how viral and host factors impact disease manifestation.

Discovery of Viruses

Tobacco Mosaic Virus (TMV) was discovered by Iwanowski in 1892.
Stanley in 1935 crystallized TMV, proving it's a virus.
Electron microscopy revealed a rod-shaped, helical structure of TMV.

Definition and Properties of a Virus

Viruses are non-filterable through bacteriological filters.
They are obligate intracellular parasites.
Dependent on a host cell for energy and protein synthesis.
Contain either DNA or RNA, but not both.
An infective particle has a protein coat (naked) or an envelope.
They reproduce by self-assembling individual parts, not binary fission.

Viral Structure + General Concepts

The presentation covers viral structure and related concepts.

What Are the Different Features of Viruses That Have Lent Themselves to How Viruses Are Classified?

Viral properties like size, morphology, genetic structure, and mode of replication aid in classification.
Viral classification is based on characteristics like the presence of an envelope, shape, genome type, transmission modes, and target cells.
It's important to utilize these characteristics for classifying viruses.

Schematic Diagram of an Infective Viral Particle

The delivery system protects the viral payload from environmental harm during transit.
The payload contains the viral genome along with enzymes for initial replication steps.

The Payload: DNA or RNA

DNA viruses can have single or double-stranded linear or circular genomes; continuous or nicked ends.
RNA viruses have single or double-stranded genomes; linear and may be segmented.

Components of the Basic Virion

The core contains the viral genome (DNA or RNA) and associated enzymes.
The capsid is a protein shell encasing the nucleic acid—either helical, icosahedral, or complex.
Nucleocapsids are capsids combined with nucleic acid.
Some viruses have an envelope derived from a host cell.
The matrix protein maintains virion structure.
A virion is a complete infectious virus particle

Capsid Symmetry (Structure)

Icosahedral symmetry is a common capsid structure, exemplified by adenoviruses.
Helical symmetry is another prevalent structure, seen in Ebola viruses.
Complex symmetries exist for some viruses like poxviruses and bacteriophages.

Exception to 2 Types of Symmetry: Complex Symmetry Viruses

Poxviruses and bacteriophages are examples of complex symmetry structures.

Consequence of Naked/Non-Enveloped Capsids on Viruses

Naked viruses are more resistant to environmental factors.
They are transmitted via non-living surfaces (fomites).
They can persist in the environment for longer durations.

Consequence of Envelope on Viruses

Enveloped viruses are susceptible to inactivation by environmental factors.
Enveloped viruses are transmitted through bodily fluids or aerosols.
They are easily inactivated by drying, detergents, or changes in temperature.
They need moisture to survive.

Consequence of Envelope on Viruses (Continued)

Viruses that are enveloped can be transmitted through droplets or secretions, blood, or organ transplants.
They can't survive in the gastrointestinal tract.

General Order of Microbial Resistance

Resistance to biocides depends on factors like size, presence of an envelope, and other characteristics.

Naming and Classification of Viruses

Viral classification is determined by the structure and genetic properties of the virus.
Naming and classifying viruses involves using the unique traits that define the species.

Type of Capsids + Genome Type

Categorization of viruses based on capsid shape and genome type (e.g., DNA or RNA).

Classification: DNA Viruses of Medical Importance

DNA viruses associated with human diseases are categorized into seven families

Classification: RNA Viruses of Medical Importance

RNA viruses of medical concern can be categorized into at least 14 families.

Viral Replication

The cycle of viral replication involves the steps of attachment, penetration, uncoating capsid, biosynthesis of protein and nucleic acid, assembly, and release
Presentation on viral replication.

Step 1 (Attachment/Adsorption)

Viral attachment proteins (VAPs) and cell receptors determine attachment.

Step 2: Penetration/Entry

Entry mechanisms vary depending on the presence or absence of a viral envelope.

How Do Most Enveloped Viruses Gain Entry into a Host Cell?

Attachment to surface receptors, penetration of host-cell membranes by fusion proteins, and fusion of the viral and cell membranes are the processes that accomplish viral entry.

How Do Non-Enveloped & Some Enveloped Viruses Gain Entry into a Host Cell

Viral entry via fusion of membranes, or by endocytosis.

Fusion | Syncytium Formation in Some Viral Infections

Fusion involves infected cells fusing to form multinucleated structures called syncytia.
This process is driven by viral fusion proteins.

Step 3: Uncoating/Release of Nucleic Acid from Capsids

The genome is released from the capsid.
Release of DNA from the capsid differs between DNA and RNA viruses.

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

Protein synthesis and genome replication of the virus take place.

What Are the Rules of Viral Replication?

Location specifies replication of viral genomes.

Step 5: Assembly

Viral components self-assemble to form new virions.
Genome and core enzymes are encapsulated.

Step 6: Release

Newly formed virions leave the cell by lysis or budding, the exit route varies based on the type of virus

Overview of Assembly & Release

Enveloped viruses release via budding; non-enveloped release via cell lysis.

Factors Influencing Disease Manifestation

How viruses and the host's condition affect the observable symptoms of a disease.

How Come Some People Get Sick While Others Don't?

Viral and host factors influence disease severity and manifestation.

Factors which influence disease

The interplay between viral and host factors influences the outcome of viral infections.

On Your Own

Suggestions for independent student activities.

To Do: Draw and Label the Basic Virion

Drawing different virion structures for understanding the various components involved.

To Do: List the DNA and RNA Virus Families

Listing of DNA and RNA families for further learning and memorization purposes.

To Do: List Major Virus Families Based on Their Genome, Capsid & Envelope Status

Categorizing virus families based on their characteristics for better understanding and recall.

To Do: List the DNA Virus Families Along with Their Replication Schemes

Listing of replications schemes.

Alternate View: Strategies for DNA Virus Replication

Various techniques for DNA viruses to replicate.

Alternate View: Strategies for RNA Virus Replication

Various methods for RNA viruses to replicate.

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

Locating viral replication.

Example: Norovirus

Norovirus is a common, incredibly contagious virus type.
Norovirus, a common cause of viral gastroenteritis.

Example: HIV

HIV, the virus causing AIDS, has various viral characteristics.
HIV, the cause of AIDS, has specific infection stages and mechanisms.

Example: Varicella-Zoster Virus (VZV)

VZV triggers chickenpox, which may lead to zoster later in life.

Additional Thought Questions

Questions related to viral genome replication location, poxvirus propagation, and orthomyxovirus behavior within cells.

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Description

Test your knowledge on the Baltimore classification of Hepadnaviruses and their replication mechanisms. This quiz covers essential concepts including the role of reverse transcriptase and mRNA production in Group VII viruses. Perfect for students studying virology or molecular biology.