MICROBIO 2.1 - VIRUSES

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Questions and Answers

What is the function of the M protein?

  • It helps the virus evade the host's immune system.
  • It facilitates the release of the virus from the host cell. (correct)
  • It controls the assembly of new viral proteins.
  • It plays a role in integrating the viral genome into the host's DNA.

Which of the following statements accurately describes the difference between a lytic and a lysogenic virus?

  • Lytic viruses are always lethal to their host cells, while lysogenic viruses only become lethal under certain conditions. (correct)
  • Lysogenic viruses integrate their genome into the host's DNA, while lytic viruses do not. (correct)
  • Lytic viruses replicate through budding, while lysogenic viruses replicate through cell lysis.
  • Lysogenic viruses are non-enveloped, while lytic viruses are enveloped.

In the context of viral replication, what is the role of recombination?

  • The process where a virus's gene products are supplemented by another virus.
  • The process where viruses exchange genetic information, leading to the creation of hybrid strains. (correct)
  • The process where different viruses combine to create a new, more infectious virus.
  • The final stage of viral replication when new viral particles are released from the host cell.

What is the difference between reassortment and complementation?

<p>Reassortment involves the creation of a hybrid strain with a combination of genetic material from two different viruses, while complementation involves the rescue of a non-functional virus by another virus. (B)</p> Signup and view all the answers

Which statement best describes phenotypic mixing?

<p>A virus takes on the surface proteins of another virus, allowing it to evade the host's immune system. (C)</p> Signup and view all the answers

What are the four main routes of entry for viruses into the human body?

<p>Respiratory, Gastrointestinal, Transcutaneous, Sexual (C)</p> Signup and view all the answers

Which type of viral infection is characterized by continuous shedding of virus particles after an acute illness, sometimes without host death, and is usually caused by RNA viruses?

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

Which of the following is an example of a virus that can spread through both skin and neural routes?

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

Which of the following is an example of a viral infection that is considered a latent infection?

<p>Herpes Simplex Virus (HSV) (B)</p> Signup and view all the answers

What is the name of the cellular stress response that involves the sequestration and degradation of viruses within cytoplasmic organelles?

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

Which of the following is NOT an example of an extrinsic protective mechanism against viral infection?

<p>Apoptosis (C)</p> Signup and view all the answers

What are the two main ways that viruses can spread among people?

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

What is the term used to describe the presence of a high concentration of virus particles in the bloodstream?

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

Which of the following statements accurately describes the role of bacteriophages in ecosystems?

<p>Bacteriophages help to control bacterial populations, preventing them from becoming dominant. (D)</p> Signup and view all the answers

Why are viruses considered neither prokaryotic nor eukaryotic?

<p>Viruses cannot reproduce independently, relying on host cells for replication. (C)</p> Signup and view all the answers

What is the significance of the "spillover event" in the context of viral infections?

<p>It refers to the transfer of viruses from one species to another, including humans. (C)</p> Signup and view all the answers

Which of the following is NOT considered a route of entry for viruses into the body?

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

What is the primary function of the viral capsid?

<p>To protect the viral genetic material from degradation. (B)</p> Signup and view all the answers

What is the fundamental difference between positive-sense RNA viruses and negative-sense RNA viruses?

<p>Positive-sense RNA viruses can be directly translated into proteins, while negative-sense RNA viruses need to be transcribed into messenger RNA (mRNA) first. (D)</p> Signup and view all the answers

Why is it important to understand the structure of a virus?

<p>All of the above. (D)</p> Signup and view all the answers

What is the structural difference between adenoviruses and reoviruses?

<p>Adenoviruses infect the respiratory system while reoviruses infect the enteric system. (C)</p> Signup and view all the answers

Which of the following statements accurately describes the role of glycoproteins in viral infection?

<p>They can serve as virus-associated pyramids (VAPs) that bind to host cells. (C)</p> Signup and view all the answers

Which of the following statements describes the key difference between enveloped and nonenveloped viruses?

<p>Enveloped viruses are more easily transmitted in fluids than nonenveloped viruses. (D)</p> Signup and view all the answers

What is the primary function of the viral envelope?

<p>To facilitate the attachment and entry of the virus into host cells. (D)</p> Signup and view all the answers

Which of the following features is NOT characteristic of icosahedral capsids?

<p>They are typically helical in shape. (B)</p> Signup and view all the answers

Why are certain glycoproteins referred to as hemagglutinins?

<p>They cause the clumping of erythrocytes (red blood cells). (C)</p> Signup and view all the answers

Which of the following statements is TRUE regarding the classification of viruses based on their morphology?

<p>Viruses with a helical nucleocapsid are always enveloped. (C)</p> Signup and view all the answers

What is the difference between a nucleocapsid and a capsid?

<p>A capsid is the protein shell surrounding the viral genome, while a nucleocapsid includes both the capsid and the genome. (C)</p> Signup and view all the answers

What is the significance of glycoproteins as major antigens?

<p>They trigger the host's immune response by inducing the production of antibodies. (A)</p> Signup and view all the answers

Which of the following statements correctly describes the role of attachment proteins in viral infection?

<p>Attachment proteins bind to specific receptors on the host cell surface, facilitating the initial step of viral entry. (A)</p> Signup and view all the answers

During the entry stage of viral infection, what are the two primary mechanisms by which a virion can enter a host cell?

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

What is the primary function of uncoating in the viral infection cycle?

<p>To release the viral genome from the capsid, making it accessible for replication. (D)</p> Signup and view all the answers

What is the main difference between the synthesis of viral proteins and nucleic acids in DNA viruses and RNA viruses?

<p>DNA viruses replicate in the nucleus while most RNA viruses replicate in the cytoplasm. (D)</p> Signup and view all the answers

Which of the following statements correctly describes the role of RNA-dependent RNA polymerase in the replication of RNA viruses?

<p>RNA-dependent RNA polymerase catalyzes the synthesis of RNA from an RNA template, allowing for the replication of viral RNA. (C)</p> Signup and view all the answers

What is the key difference between positive-sense and negative-sense RNA viruses?

<p>Positive-sense RNA viruses can immediately begin transcription, while negative-sense viruses require an intermediate step to produce mRNA. (C)</p> Signup and view all the answers

Why are naked positive-sense viral genomes considered infectious?

<p>They can directly act as mRNA for protein synthesis, allowing for immediate replication. (B)</p> Signup and view all the answers

What is the significance of 'tissue tropism' in viral infection?

<p>It determines the specific cell types that a virus can infect. (B)</p> Signup and view all the answers

Which of the following statements accurately describes the role of 'immediate-early' and 'early' transcription in DNA viral replication?

<p>Immediate-early genes encode proteins that regulate host cell transcription and facilitate viral replication, while early genes encode proteins involved in viral DNA replication. (B)</p> Signup and view all the answers

What is the primary function of 'late' transcription in DNA viral replication?

<p>To synthesize viral proteins needed for the assembly of new viral particles. (A)</p> Signup and view all the answers

Flashcards

Viral Diversity

Over 1.7 million undiscovered viruses exist in mammals and birds.

Spillover Event

When viruses transfer from animals to humans, potentially causing outbreaks.

Importance of Viruses

Most viruses support ecosystems and aren't harmful to humans.

Bacteriophages

Viruses that specifically infect bacteria, regulating bacterial populations.

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Viral Life Cycle

The process virus goes through to replicate and spread, including six key stages.

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RNA vs DNA Viruses

Viruses can have RNA or DNA as their genetic material and differ in replication.

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Intrinsic Protective Mechanisms

Body's natural defenses, such as skin and immune cells against viruses.

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Viral Structure Basics

Viruses consist of a capsid and sometimes an envelope, influencing how they infect.

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Icosahedral Capsid

A viral capsid shape with 20 triangular faces and 12 vertices, resembling a soccer ball.

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Helical Nucleocapsid

A type of viral capsid that consists of varied subunits with a tightly packed spherical core.

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Nucleocapsid

The combination of viral nucleic acid and its protective capsid.

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Viral Envelope

A lipid membrane surrounding some viruses, containing proteins and glycoproteins.

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Nonenveloped Virus

Viruses without a lipid envelope, more stable and resistant to environmental changes.

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Enveloped Virus

Viruses that have a lipid envelope, more fragile and sensitive to environmental factors.

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Virus Associated Pyramids (VAPs)

Glycoproteins that bind to specific structures on target cells, aiding virus entry.

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Spike Glycoproteins

Protruding viral proteins that help in attachment and elicit immune response.

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Glycoproteins

Proteins on the virus surface that can be linked to carbohydrates, important for immunity.

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VIRION

The complete, infective form of a virus outside a host cell; also known as a viral particle.

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Negative-sense RNA

A viral RNA that must be transcribed into positive RNA for protein synthesis.

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Recombination

Genetic information exchange between viruses or a virus and its host.

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Reassortment

Hybrid strain creation from viruses with segmented genomes.

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Complementation

Process where a mutated virus relies on another virus for functional proteins.

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Lytic vs. Lysogenic viruses

Lytic viruses burst cells, while lysogenic viruses integrate into the host genome without killing the cell immediately.

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Attachment

The process by which a virus binds to a host cell using adhesion receptors.

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Naked viruses

Viruses without a lipid envelope, relying on capsid regions for attachment.

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Entry

The mechanism through which a virus enters a host cell, either by membrane fusion or endocytosis.

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Uncoating

The process of disassembling the virus's capsid to release the viral genome into the host cell.

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Synthesis of proteins & nucleic acids

The production of viral proteins and genetic material, dependent on the virus type.

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DNA viruses

Viruses that use DNA as their genetic material, typically replicating in the nucleus.

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RNA viruses

Viruses that use RNA as their genetic material, often replicating in the cytoplasm.

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Positive-sense strand viruses

Viruses with RNA that can act as mRNA for immediate protein synthesis.

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Negative-sense strand viruses

Viruses whose RNA does not act as mRNA and requires transcription before translation.

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Capsid Shapes

The two basic shapes of virus capsids: icosahedral and helical.

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Virus Entry Routes

The main pathways viruses use to enter a host: respiratory, gastrointestinal, transcutaneous, and sexual routes.

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Exogenous Virus

Viruses that originate from outside the host, leading to most viral diseases.

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Endogenous Virus

Viruses that reactivate from within the host cell, like HSV or VZV.

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Vertical Spread

Virus transmission from mother to fetus during pregnancy.

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Horizontal Spread

Spread of viruses among individuals in the same population.

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Incubation Period

Time between exposure to a virus and appearance of symptoms.

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Types of Viral Infections

Three categories: acute, chronic, and latent infections with differing outcomes for the host.

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Neutralizing Antibodies

Antibodies that specifically destroy the infectivity of a virus.

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Study Notes

Viral Structure

  • Viruses are neither prokaryotic nor eukaryotic.
  • Viruses lack the characteristics of life as they cannot reproduce independently.
  • Viruses are obligate intracellular parasites.
  • Viruses have a capsid (single or double protein layer).
  • Nucleic acid (RNA or DNA) in the core
  • Glycoproteins on the outer surface of envelopes (if present)
  • Icosahedral (soccer ball shape) and helical.
  • Viruses are measured in nanometers (nm).
    • Poliovirus - 32 nm
    • Rotavirus - 100 nm
    • Human papillomavirus - 60 nm
    • Adenovirus - 110 nm
    • Semliki Forest virus - 70 nm
    • Influenza virus - 80-120 nm
    • Paramyxovirus - 150-350 nm
    • Smallpox virus - 200 x 300 nm

Viral Classification

  • Viruses classified by structure, biochemical characteristics, and type of replication.
  • Examples include Picornavirus, Togavirus, Retrovirus, Adenovirus, Reovirus.

Viral Life Cycle

  • Viruses have a specific life cycle.
  • 6 essential stages are:
    • Attachment
    • Entry
    • Uncoating
    • Synthesis of protein & nucleic acid
    • Assembly
    • Release

Viral Genetics

  • Viral genomes can be DNA or RNA.
  • Various mechanisms exist. They include recombination, reassortment, and complementation.
  • Also, phenotypic mixing occurs.

Viral Properties and Consequences

  • Viruses are not living.
  • Viruses must be infectious to endure in nature.
  • Viruses must use host cells to produce their components (mRNA, protein).
  • Viruses must encode any processes not provided by the host cell.
  • Viral components self-assemble.
  • Viral morphology varies and depends on the type of virus.

Types of Viral Infections

  • Acute infection: Virus undergoes multiple rounds of replication.
  • Chronic infection: Virus replicates but host does not successfully eliminate them.
  • Latent infection: Virus does not produce progeny.

Viral Damage

  • Interactions between host and virus lead to the development of signs and symptoms.
  • Intrinsic and extrinsic protective mechanisms exist within the host and prevent damage.

Preventative Measures

  • Vaccination is a key preventative measure.
  • Other preventive steps include hand-washing, avoiding sick individuals, wearing masks, and staying home when sick.

Encounter & Entry

  • Viruses enter the body through four main routes: respiratory, gastrointestinal, transcutaneous, or sexual.
  • Viral diseases come either from the environment (exogenous) or from within the host (endogenous).

Spread & Replication

  • Viruses spread via vertical (during pregnancy) or horizontal transmission among members of the host population (person-to-person).
  • The virus replicates via various pathways (neural, hematogenous).

Test your knowledge!

  • There are two main capsid shapes: Icosahedral & helical.
  • There are 6 main steps of viral replication: Attachment, Entry, Uncoating, Synthesis of protein & nucleic acid, Assembly, and release.

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