Lecture 5
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Questions and Answers

Which of the following is the most common type of symmetry observed in virus structures?

  • Complex
  • Helical
  • Pleomorphic
  • Icosahedral (correct)

What is a key feature of segmented viruses?

  • They possess multiple RNA molecules. (correct)
  • They lack a viral envelope.
  • They contain a DNA genome.
  • They have a single, circular RNA molecule.

Which suffix is typically used to denote a virus family?

  • -viridae (correct)
  • -oviridae
  • -mycota
  • -virus

In the context of virus nomenclature, how are viruses usually referred to?

<p>By their species name. (A)</p> Signup and view all the answers

Why is understanding the virus infection cycle crucial from a medical point of view?

<p>Because viral enzymes, which are potential targets for antiviral drugs, are produced during replication. (B)</p> Signup and view all the answers

What role do glycoproteins on the host cell membrane play in viral infection?

<p>They serve as receptors for virus attachment. (D)</p> Signup and view all the answers

What determines the specificity of a virus for a particular cell type?

<p>The presence of specific protein spikes on the virus that match host cell receptors. (B)</p> Signup and view all the answers

The virus HIV, requires two receptors (at least) for entering a cell, what does this demonstrate?

<p>That single receptors are not always adequate for effective virus attachment. (A)</p> Signup and view all the answers

What is the primary characteristic that distinguishes viruses from living organisms?

<p>Their dependence on host cells for replication. (A)</p> Signup and view all the answers

Which statement best describes the structure of a non-enveloped virus?

<p>It consists of a protein coat called a capsid surrounding genetic material. (C)</p> Signup and view all the answers

What is the role of bacteriophages in the environment?

<p>To limit bacterial populations by causing cell lysis. (C)</p> Signup and view all the answers

What is the typical size range of most viruses?

<p>10-1000 nanometers (B)</p> Signup and view all the answers

How do enveloped viruses typically acquire their lipid membrane?

<p>By modifying the host cell's cytoplasmic membrane. (D)</p> Signup and view all the answers

What genetic material can be found in a virus?

<p>Either DNA or RNA but never both (A)</p> Signup and view all the answers

Which of the following accurately describes the capsomeres?

<p>They are the protein subunits that make up the viral capsid. (C)</p> Signup and view all the answers

What is the function of the attachment proteins, or spikes, on viruses?

<p>To bind the virus to the host cell. (A)</p> Signup and view all the answers

Which process do enveloped viruses use to enter a host cell?

<p>Membrane fusion or endocytosis. (D)</p> Signup and view all the answers

How do naked viruses typically enter a host cell?

<p>By endocytosis only. (A)</p> Signup and view all the answers

When does uncoating of the viral genome occur in the replication process?

<p>Immediately after viral entry but before replication. (D)</p> Signup and view all the answers

What are the two main steps involved in the production of viral particles?

<p>Expression of viral genes and synthesis of multiple copies of the viral genome. (D)</p> Signup and view all the answers

What is the primary mechanism by which most enveloped viruses are released from the host cell?

<p>Budding from the plasma membrane. (D)</p> Signup and view all the answers

How are naked viruses released from a host cell?

<p>By triggering apoptosis of cell and consequent lysis. (D)</p> Signup and view all the answers

Which event is NOT a common mechanism for the release of viral particles from a cell?

<p>Direct extrusion of virions through cell pores. (C)</p> Signup and view all the answers

What characterizes an acute viral infection?

<p>Sudden onset of symptoms of a relatively short duration. (A)</p> Signup and view all the answers

What is the primary cause of disease symptoms following a viral infection?

<p>Localized or widespread tissue damage due to cell death and the immune response (D)</p> Signup and view all the answers

Which of the following characterizes a chronic viral infection?

<p>Continuous production of low levels of viral particles with or without symptoms. (C)</p> Signup and view all the answers

How does a latent viral infection differ from a chronic viral infection?

<p>Latent infections feature a silent viral genome that can reactivate later, whereas chronic infections have continuous production, and transmission of viruses. (D)</p> Signup and view all the answers

What is a 'provirus' in the context of latent viral infections?

<p>A viral genome that can be integrated into the host's genome or exist independently as in HIV. (B)</p> Signup and view all the answers

Which statement accurately describes the reactivation of latent viruses such as HSV-1?

<p>Reactivation causes the virus to resume its active state, often triggered by unidentified physiological or immunological shifts. (D)</p> Signup and view all the answers

What is the main distinction between a benign tumor and a malignant tumor?

<p>Malignant tumors have the capability to spread to distant sites, which is not a feature of benign tumors. (A)</p> Signup and view all the answers

Which class of viruses is primarily associated with causing virus-induced tumors in humans, excluding retroviruses?

<p>DNA viruses (A)</p> Signup and view all the answers

What is a defining characteristic of acute viral infections?

<p>They are characterized by the host immune system gradually eliminating the virus over a period of days to months. (C)</p> Signup and view all the answers

Which method is used to grow viruses that requires a living host?

<p>Living animals (B)</p> Signup and view all the answers

What is the term for the distinct morphological alterations in infected cells in cell culture caused by viral replication?

<p>Cytopathic effect (A)</p> Signup and view all the answers

Which of the following is a characteristic of an inclusion body?

<p>It is the site of viral replication. (C)</p> Signup and view all the answers

Which method of virus quantitation is considered the most precise and commonly used?

<p>Plaque assay (A)</p> Signup and view all the answers

What is the significance of plaques in a plaque assay?

<p>They represent areas of lysed infected cells. (A)</p> Signup and view all the answers

When might virion counting with an electron microscope be helpful?

<p>When you have a pure preparation of viruses. (C)</p> Signup and view all the answers

What is the primary function of using embryonated chicken eggs in virology?

<p>To prepare vaccines (C)</p> Signup and view all the answers

Which of the following is a typical effect of cytopathic effect?

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

What is the primary criterion for determining the titer of a virus in an assay?

<p>The dilution at which 50% of the inoculated hosts are infected or killed (B)</p> Signup and view all the answers

Which viral group is known to cause hemagglutination of red blood cells?

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

Which of the following characteristics is unique to prions?

<p>They contain only protein and no nucleic acid (A)</p> Signup and view all the answers

What is the term used to describe the group of diseases caused by prions, characterized by the spongy-like appearance of neural tissue?

<p>Transmissible spongiform encephalopathies (TSEs) (C)</p> Signup and view all the answers

Which statement best distinguishes PrPC from PrPsc?

<p>PrPC is sensitive to protease digestion and PrPsc is resistant. (B)</p> Signup and view all the answers

How do prions propagate in the host?

<p>By converting host proteins into the prion form (D)</p> Signup and view all the answers

Why are prions not inactivated by UV light or nucleases?

<p>Because they lack nucleic acids and are essentially pure protein (B)</p> Signup and view all the answers

What method is used to measure the hemagglutination titer of a virus?

<p>By observing the extent of red blood cell clumping with varying virus dilutions (D)</p> Signup and view all the answers

Flashcards

What are viruses?

Viruses are non-living infectious agents that cannot replicate on their own.

What are bacteriophages?

Bacteriophages are viruses that infect bacteria.

How are viruses classified?

Viruses are classified based on the type of cell they infect. Some infect prokaryotic cells, others infect eukaryotic cells.

How big are viruses?

Viruses are much smaller than the cells they infect and can only be seen using an electron microscope.

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What is the structure of a virus?

Viruses contain either DNA or RNA, never both, surrounded by a protective protein coat called a capsid.

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What is an enveloped virus?

A virus with an additional lipid membrane surrounding its capsid is called an enveloped virus.

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What are attachment proteins?

Attachment proteins, or spikes, on the surface of viruses allow them to bind to host cells.

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What shapes can viruses have?

Viruses can have three main shapes: helical, icosahedral, and complex.

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Icosahedral Symmetry

A type of viral symmetry where protein subunits are arranged in equilateral triangles, giving the virus a spherical appearance, like a soccer ball.

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Helical Viruses

Viruses with a long, cylindrical shape, often described as rod-shaped.

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Complex Viruses

Viruses with complex and irregular structures, often with multiple components, like in bacteriophages.

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Attachment (Adsorption)

The initial step in viral infection where a virus attaches to the surface of a host cell.

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Virus Attachment Protein

A protein on the surface of a virus that binds to specific receptors on the host cell.

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Host Cell Receptor

A molecule on the surface of a host cell that is recognized and bound by viral attachment proteins.

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Host Specific Virus

A virus that can only infect a single or limited number of cell types.

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Virally Coded Enzymes

Viral enzymes that are encoded by the virus's genome and are essential for viral replication.

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Cell Culture

A technique used to grow viruses in laboratory conditions, utilizing living cells like primary cultures, established cell lines, and tumor cell lines.

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Cytopathic Effect (CPE)

Changes in the appearance of cells infected by viruses, detectable under a microscope. Cells may change shape, detach, lyse, or fuse into multinucleated cells.

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Inclusion Body

A distinct region within an infected cell where viral replication occurs, often visible as a dense body under a microscope.

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Plaque Assay

A method for quantifying viruses based on the formation of clear zones (plaques) in a cell monolayer, representing the lysis of infected cells.

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Virion Counting

A technique used to directly count virus particles in a sample using an electron microscope.

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Quantal Assays

A way to estimate the concentration of viruses in a sample by determining the dilution at which a certain effect (like cell death) occurs.

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Embryonated Chicken Egg Cultivation

A technique used to propagate viruses in embryonated chicken eggs, often for vaccine production, as in the case of influenza viruses.

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Chronic Infections

Viral infections resulting in continuous viral production and symptoms for extended periods (e.g., Hepatitis B).

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Latent Infections

Viral infections where the viral genome remains inactive in the host cell, but can reactivate later causing symptoms (e.g., Herpes Simplex Virus).

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Provirus

The inactive form of a virus's genome present within a host cell during latent infections. It can either integrate with the host's DNA or exist independently.

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Benign Tumors

Non-cancerous growths that do not spread to other parts of the body.

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Malignant Tumors

Cancerous growths that can spread to other parts of the body (metastasis).

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Metastasis

The spread of cancer cells from their original location to other parts of the body.

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Immune Response to Viral Infections

The process where immune cells identify and destroy virus-infected cells, essentially controlling the infection.

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Retroviruses

Viruses that can integrate their genetic material into the host's genome, potentially leading to long-term infections or even cancer (e.g., HIV).

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How do enveloped viruses enter cells?

Entry of enveloped viruses into host cells can happen through membrane fusion where the viral envelope directly merges with the host cell membrane, or through endocytosis where the virus is engulfed by the host cell.

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How do naked viruses enter cells?

Naked viruses lack an envelope and enter host cells solely through endocytosis, a process where the host cell engulfs the virus.

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What is uncoating?

Uncoating is a crucial step in the viral replication cycle where the viral capsid, the protective protein coat surrounding the viral genome, is removed. This release of the viral genome enables further steps in the replication process.

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What happens during the synthesis phase of viral replication?

Viral proteins are synthesized using the host cell's machinery, and viral genomes are replicated according to the virus's specific replication strategy. This ensures the production of new viral components for assembly.

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What is viral assembly?

Assembly refers to the process where new viral particles are formed. The viral capsid is assembled around the viral genome, incorporating any necessary enzymes or proteins, forming complete and infectious virions.

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How are enveloped viruses released?

Enveloped viruses are released from the host cell through budding, which involves acquiring an envelope from the host cell's membrane. This usually doesn't kill the host cell.

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How are naked viruses released?

Naked viruses are released when the host cell dies. The cell's lysis, or breakdown, releases the newly formed virions.

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What are acute infections?

Acute infections are characterized by sudden onset and relatively short duration of symptoms. The infection is productive, leading to the host cell's death with or without virus release.

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Viral Titer

A measurement of the viral concentration in a sample, indicating the dilution at which 50% of inoculated hosts show infection or death. It is reported as ID50 (infective dose) or LD50 (lethal dose).

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Hemagglutination

The ability of certain viruses to clump red blood cells (RBCs) due to interaction with their surface. This is a feature of some viruses, like influenza.

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Prion

A type of infectious agent consisting only of protein, with no nucleic acid. It is responsible for several slow, fatal diseases in humans and animals, causing brain deterioration and sponge-like appearance.

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PrPC (Prion Protein Cellular)

The normal, non-disease causing form of prion protein found in healthy cells, especially neurons. It is susceptible to protease digestion.

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PrPsc (Prion Protein Scrapie)

The abnormal, disease-causing form of prion protein, responsible for prion diseases. It is resistant to protease digestion.

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Prion Resistance

Prions are resistant to inactivation methods that work for most infectious agents. They are not inactivated by UV light, nucleases, heat, or common chemical treatments.

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Prion Replication

Prions replicate by converting the normal PrPC protein into the disease-causing PrPsc protein. This process accelerates the spread of abnormal prion protein.

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Prion Diseases

Prions can cause a variety of neurodegenerative diseases in humans and animals. These diseases are characterized by slow progression, long incubation periods, and inevitably lead to death.

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Study Notes

Viruses, Viroids, and Prions

  • Viruses are inert particles, unable to metabolize or replicate independently. They are obligate intracellular parasites.
  • Viruses are non-living infectious agents, not organisms.
  • Viruses are categorized based on the types of cells they infect (prokaryotic or eukaryotic).
  • Bacteriophages are viruses that infect bacteria. They are important in understanding molecular biology, virus-host relationships, and horizontal gene transfer in bacteria. They also contribute to controlling bacterial populations and preventing bacterial infections.
  • Most viruses are much smaller than the cells they infect (100-1000 fold smaller).
  • Virus sizes range from 10nm to 800nm.
  • Viruses are too small to be seen by a light microscope, requiring electron microscopes for visualization.
  • Viruses have a protein coat (capsid), made of capsomeres, surrounding their genetic material (DNA or RNA).
  • Naked viruses have only the capsid. Enveloped viruses have a lipid membrane surrounding the capsid.
  • Viruses have three basic shapes: icosahedral, helical, and complex.
  • Animal viruses are classified based on genome structure (DNA or RNA, single or double-stranded, segmented or single molecule), virus particle structure (isometric, helical, or pleomorphic), and presence or absence of an envelope.
  • Some RNA viruses have multiple RNA molecules (segmented viruses).
  • Animal viruses are divided into families and are named using the -viridae suffix.
  • Viruses are commonly referred to by their species name, unlike other microorganisms that use taxonomic classification.
  • Virus replication involves several stages. These include attachment, entry/uncoating, synthesis of viral proteins, assembly, and release, with each stage affected by the virus's characteristics.
  • The virus's replication cycle affects cells in the host and leads to the development of symptoms.
  • Understanding virus infection cycles is vital, as viral enzymes are potential targets for antiviral drugs.
  • Virus replication proceeds with distinct but interrelated events: expression of viral genes for structural and catalytic proteins (enzymes) necessary for replication, and synthesis of multiple genome copies.
  • There are differing strategies for DNA and RNA viral replication processes.
  • Retroviruses, unique RNA viruses, use reverse transcription to copy their RNA genome into DNA for replication and integration into host DNA.
  • Enveloped viruses release by budding, acquiring the envelope from the host cell's membrane. Naked viruses are released when the host cell dies.
  • Viral infections can be acute (sudden onset) or persistent (long-term).
  • Acute infections result in productive infection, cell death, localized or widespread tissue damage.
  • Persistent infections include chronic infections (continuous viral production) and latent infections (viral genome remains inactive until reactivated).
  • Viruses like HIV have mixed characteristics (both acute and persistent).
  • Certain types of viruses can cause tumors.
  • Methods are used to quantify viruses, such as plaque assays, virus counting with electron microscopes, hemagglutination, and quantal assays.
  • Cell cultures are utilized to cultivate and study viruses.
  • Methods for studying virus growth includes techniques such as cell or tissue culture.
  • Infected cells undergo morphological change (cytopathic effect), altering shape, detach from the surface, or lyse.
  • Certain viruses fuse infected cells, forming giant multinucleated cells (syncytia). Formation of inclusion bodies is a feature of certain viruses.
  • Prions are infectious agents composed of proteins only, with no nucleic acid.
  • Prions cause fatal neurodegenerative diseases, such as Creutzfeldt-Jakob disease, in humans and animals. They accumulate in neural tissue.
  • For unknown reasons, the accumulation of prion protein is associated with brain deterioration, as nerve cells die and sponge-like holes develop in brain tissue.
  • Prion diseases exhibit characteristic sponge-like patterns in the brain tissue, contributing to the general term—transmissible spongiform encephalopathies (TSEs), for these diseases.
  • Prion diseases can be transmitted within the same species, but transmission between species can vary depending on the prion strain.
  • Prions are resistant to heat and chemicals commonly used to inactivate other infectious agents
  • Prions catalyze the conversion of normal proteins into abnormal prion proteins.

Next steps

  • Next lecture is about microbial growth.

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Viruses, Viroids and Prions Lecture Notes PDF

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This quiz covers key concepts related to viruses, viroids, and prions, focusing on their structures, classifications, and roles in infections. Understand the differences between these infectious agents and their impact on cellular biology. Explore the fascinating world of microbiology and discover how viruses behave within their host organisms.

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