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Microbiology: Viruses and Prions Study Guide – Step-by-Step Guidance

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Q1. List at least 4 properties of viruses.

Background

Topic: General Properties of Viruses

This question tests your understanding of the fundamental characteristics that define viruses and distinguish them from other microorganisms.

Key Terms:

  • Virus: A microscopic infectious agent that can only replicate inside the living cells of an organism.

  • Obligate intracellular parasite: Requires a host cell to reproduce.

Step-by-Step Guidance

  1. Think about what makes viruses unique compared to bacteria, fungi, or protozoa. Consider their structure, replication, and dependence on host cells.

  2. Recall that viruses are not considered living organisms by many scientists because they lack certain cellular machinery.

  3. List properties such as their size, genetic material, and how they reproduce.

  4. Consider properties like their ability to mutate, their lack of metabolism, and their specificity for host cells.

Try solving on your own before revealing the answer!

Final Answer:

  • Viruses are acellular (not made of cells).

  • They contain either DNA or RNA as genetic material, but never both.

  • They cannot reproduce independently; they require a host cell.

  • They do not carry out metabolism on their own.

  • They are much smaller than bacteria, typically measured in nanometers.

These properties distinguish viruses from other types of microorganisms.

Q2. Define host range and state what determines host range.

Background

Topic: Virus-Host Interactions

This question is about the concept of host range and the factors that influence which organisms or cells a virus can infect.

Key Terms:

  • Host range: The spectrum of host cells a virus can infect.

  • Receptor: A molecule on the host cell surface that a virus recognizes and binds to.

Step-by-Step Guidance

  1. Start by defining what is meant by 'host range' in the context of virology.

  2. Think about what determines whether a virus can infect a particular cell or organism.

  3. Consider the role of viral surface proteins and host cell receptors.

  4. Remember that some viruses have a narrow host range (infecting only one species), while others have a broad host range.

Try solving on your own before revealing the answer!

Final Answer:

Host range is the spectrum of host cells or organisms that a virus can infect. It is determined primarily by the presence of specific receptors on the host cell surface that the virus can bind to, as well as the ability of the virus to enter, replicate, and assemble within the host cell.

Q3. Describe each of the following viral structures/components and indicate whether each component is found in all viruses or some viruses: Capsid, Nucleic acid (core), Envelope, Spikes.

Background

Topic: Viral Structure

This question tests your knowledge of the basic structural components of viruses and their distribution among different types of viruses.

Key Terms:

  • Capsid: Protein shell surrounding the viral genome.

  • Nucleic acid (core): The genetic material (DNA or RNA) of the virus.

  • Envelope: Lipid membrane derived from the host cell, surrounding some viruses.

  • Spikes: Glycoprotein projections from the envelope or capsid.

Step-by-Step Guidance

  1. For each structure, describe its composition and function.

  2. Indicate whether the structure is present in all viruses or only in some.

  3. Think about which structures are essential for all viruses and which are optional or variable.

  4. Consider the role of each component in the infection process.

Try solving on your own before revealing the answer!

Final Answer:

  • Capsid: Protein shell that protects the viral genome; found in all viruses.

  • Nucleic acid (core): The genetic material (DNA or RNA); found in all viruses.

  • Envelope: Lipid membrane derived from the host cell; found in some viruses (enveloped viruses), absent in others (nonenveloped viruses).

  • Spikes: Glycoprotein projections used for attachment to host cells; found in some viruses, especially enveloped viruses.

Q4. What metric unit is used to express the size of a virus?

Background

Topic: Viral Size Measurement

This question is about the standard unit used to measure the size of viruses, which are much smaller than most cells.

Key Terms:

  • Nanometer (nm): One billionth of a meter.

Step-by-Step Guidance

  1. Recall the typical size range of viruses (20–300 nm).

  2. Think about which metric unit is appropriate for measuring objects at this scale.

  3. Remember that micrometers (μm) are used for bacteria, but viruses are even smaller.

Try solving on your own before revealing the answer!

Final Answer:

The nanometer (nm) is the metric unit used to express the size of a virus.

Q5. Compare and contrast enveloped and nonenveloped viruses.

Background

Topic: Viral Structure and Classification

This question asks you to distinguish between viruses with and without an envelope, focusing on their structure and implications for infection and stability.

Key Terms:

  • Enveloped virus: Virus with a lipid membrane surrounding the capsid.

  • Nonenveloped (naked) virus: Virus lacking an envelope, consisting only of nucleic acid and capsid.

Step-by-Step Guidance

  1. Describe the structural differences between enveloped and nonenveloped viruses.

  2. Consider how the presence or absence of an envelope affects viral entry into host cells.

  3. Think about the stability of each type in the environment (e.g., resistance to drying, detergents).

  4. List examples or implications for disease transmission.

Try solving on your own before revealing the answer!

Final Answer:

  • Enveloped viruses have a lipid membrane derived from the host cell, are generally less stable outside the host, and often enter cells by membrane fusion.

  • Nonenveloped viruses lack this envelope, are more resistant to environmental stresses, and typically enter cells by endocytosis or direct penetration.

Q6. Define viral species.

Background

Topic: Virus Classification

This question is about the definition of a viral species, which is different from the definition of species in plants or animals.

Key Terms:

  • Viral species: A group of viruses sharing the same genetic information and ecological niche.

Step-by-Step Guidance

  1. Recall how species are defined for viruses, considering their genetic and ecological characteristics.

  2. Think about the criteria used by the International Committee on Taxonomy of Viruses (ICTV).

  3. Consider the importance of host range and genetic similarity.

Try solving on your own before revealing the answer!

Final Answer:

A viral species is a group of viruses sharing the same genetic information and ecological niche (host range and disease characteristics).

Q7. List at least 4 properties that are used to classify viruses.

Background

Topic: Virus Classification

This question tests your knowledge of the criteria used to group viruses into families, genera, and species.

Key Terms:

  • Genome type, capsid symmetry, presence of envelope, host range, replication strategy.

Step-by-Step Guidance

  1. Think about the main features that differ among viruses and are used for classification.

  2. Consider the type of nucleic acid (DNA or RNA), whether it is single- or double-stranded.

  3. Recall the importance of capsid shape and presence or absence of an envelope.

  4. Include host range or replication method as possible criteria.

Try solving on your own before revealing the answer!

Final Answer:

  • Type of nucleic acid (DNA or RNA)

  • Capsid symmetry (helical, icosahedral, complex)

  • Presence or absence of an envelope

  • Host range

  • Replication strategy

Q8. What is a bacteriophage and how are bacteriophage cultivated?

Background

Topic: Bacteriophages

This question is about viruses that infect bacteria and the laboratory methods used to grow them.

Key Terms:

  • Bacteriophage: Virus that infects bacteria.

  • Plaque assay: Method to quantify and cultivate bacteriophages.

Step-by-Step Guidance

  1. Define what a bacteriophage is.

  2. Describe the general method for cultivating bacteriophages in the lab.

  3. Think about the use of bacterial lawns and the appearance of plaques.

  4. Consider why bacteriophages are important in microbiology research.

Try solving on your own before revealing the answer!

Final Answer:

A bacteriophage is a virus that infects bacteria. They are cultivated by mixing phages with susceptible bacteria and plating them on agar; clear zones called plaques indicate areas where bacteria have been lysed by phages.

Q9. Briefly describe three ways of growing animal viruses.

Background

Topic: Animal Virus Cultivation

This question is about laboratory techniques for propagating animal viruses for study or vaccine production.

Key Terms:

  • Cell culture, embryonated eggs, live animals.

Step-by-Step Guidance

  1. List the three main methods used to grow animal viruses.

  2. Briefly describe how each method works.

  3. Consider the advantages and disadvantages of each method.

Try solving on your own before revealing the answer!

Final Answer:

  • Cell cultures: Viruses are grown in cultured animal cells in vitro.

  • Embryonated eggs: Viruses are injected into fertilized eggs (used for vaccine production).

  • Live animals: Viruses are grown in living animals to study pathogenesis or for isolation.

Q10. Contrast the following terms: in vivo and in vitro.

Background

Topic: Experimental Methods

This question is about the difference between experiments conducted inside living organisms versus outside in artificial environments.

Key Terms:

  • In vivo: In a living organism.

  • In vitro: In an artificial environment, such as a test tube or petri dish.

Step-by-Step Guidance

  1. Define each term separately.

  2. Think about examples of each type of experiment.

  3. Consider the advantages and limitations of each approach.

Try solving on your own before revealing the answer!

Final Answer:

In vivo refers to processes or experiments performed within a living organism, while in vitro refers to those performed outside a living organism, typically in a laboratory setting.

Q11. Define CPE (cytopathic effect):

Background

Topic: Viral Pathology

This question is about the visible effects viruses have on host cells in culture.

Key Terms:

  • Cytopathic effect (CPE): Observable changes in host cells due to viral infection.

Step-by-Step Guidance

  1. Recall what happens to cells when they are infected by viruses in culture.

  2. Think about the types of changes that can be observed (e.g., cell rounding, detachment, lysis).

  3. Consider why CPE is important for identifying viral infections.

Try solving on your own before revealing the answer!

Final Answer:

Cytopathic effect (CPE) refers to the structural changes or damage in host cells caused by viral infection, often visible under a microscope.

Q12. List several methods used to identify viruses.

Background

Topic: Viral Identification

This question is about laboratory techniques for detecting and identifying viruses.

Key Terms:

  • Serology, PCR, electron microscopy, cell culture.

Step-by-Step Guidance

  1. Think about methods that detect viral proteins, nucleic acids, or effects on cells.

  2. List at least three different approaches.

  3. Consider both direct and indirect methods.

Try solving on your own before revealing the answer!

Final Answer:

  • Serological tests (e.g., ELISA, Western blot)

  • Polymerase chain reaction (PCR) for viral nucleic acids

  • Electron microscopy

  • Observation of cytopathic effects in cell culture

Q13. Briefly describe the steps in the multiplication of a “generic” animal virus.

Background

Topic: Viral Replication Cycle

This question is about the general stages a virus goes through to replicate inside an animal cell.

Key Terms:

  • Attachment, penetration, uncoating, biosynthesis, maturation, release.

Step-by-Step Guidance

  1. List the main steps in order, starting from the virus encountering the host cell.

  2. Briefly describe what happens at each step (e.g., how the virus enters, what happens to its genome).

  3. Consider how the process differs for DNA vs. RNA viruses, but focus on the general pattern.

Try solving on your own before revealing the answer!

Final Answer:

  1. Attachment: Virus binds to specific receptors on the host cell.

  2. Penetration: Virus or its genome enters the host cell.

  3. Uncoating: Viral capsid is removed, releasing the genome.

  4. Biosynthesis: Viral genome is replicated and viral proteins are synthesized.

  5. Maturation (assembly): New viral particles are assembled.

  6. Release: New viruses exit the host cell (by lysis or budding).

Q14. Name the two general methods used for entry of animal viruses into animal cells.

Background

Topic: Viral Entry Mechanisms

This question is about how animal viruses get inside host cells.

Key Terms:

  • Endocytosis, membrane fusion.

Step-by-Step Guidance

  1. Recall the two main ways viruses can enter animal cells.

  2. Think about which method is used by enveloped vs. nonenveloped viruses.

  3. Briefly describe each method.

Try solving on your own before revealing the answer!

Final Answer:

  • Endocytosis (engulfment by the host cell)

  • Membrane fusion (fusion of viral envelope with host cell membrane)

Q15. Define oncogenic:

Background

Topic: Viruses and Cancer

This question is about the ability of some viruses to cause cancer.

Key Terms:

  • Oncogenic: Cancer-causing.

Step-by-Step Guidance

  1. Recall what the prefix 'onco-' refers to.

  2. Think about how viruses can contribute to cancer development.

  3. Formulate a concise definition.

Try solving on your own before revealing the answer!

Final Answer:

Oncogenic means having the potential to cause cancer.

Q16. Define transformation.

Background

Topic: Viral Effects on Cells

This question is about the process by which normal cells become cancerous, often due to viral infection.

Key Terms:

  • Transformation: Conversion of a normal cell into a cancerous cell.

Step-by-Step Guidance

  1. Recall what happens to a cell's growth and behavior during transformation.

  2. Think about the role of viral genes in this process.

  3. Formulate a concise definition.

Try solving on your own before revealing the answer!

Final Answer:

Transformation is the process by which a normal cell is converted into a cancerous cell, often due to the action of oncogenic viruses.

Q17. List several oncogenic viruses and the cancers they are associated with.

Background

Topic: Oncogenic Viruses

This question is about specific viruses known to cause cancer in humans.

Key Terms:

  • Human papillomavirus (HPV), Epstein-Barr virus (EBV), Hepatitis B virus (HBV), Hepatitis C virus (HCV), Human T-cell leukemia virus (HTLV).

Step-by-Step Guidance

  1. List at least three viruses known to be oncogenic.

  2. For each, name the type of cancer it is associated with.

  3. Consider both DNA and RNA viruses.

Try solving on your own before revealing the answer!

Final Answer:

  • Human papillomavirus (HPV) – cervical cancer

  • Epstein-Barr virus (EBV) – Burkitt's lymphoma, nasopharyngeal carcinoma

  • Hepatitis B virus (HBV) and Hepatitis C virus (HCV) – liver cancer (hepatocellular carcinoma)

  • Human T-cell leukemia virus (HTLV) – adult T-cell leukemia/lymphoma

Q18. Describe latency (latent infection) and name several viruses known for latency:

Background

Topic: Viral Latency

This question is about the ability of some viruses to remain dormant in the host and reactivate later.

Key Terms:

  • Latency: Dormant state of a virus within a host cell.

  • Herpesviruses, HIV.

Step-by-Step Guidance

  1. Define what is meant by latency in virology.

  2. Describe how latent viruses behave in the host.

  3. List examples of viruses that establish latency.

Try solving on your own before revealing the answer!

Final Answer:

Latency is when a virus remains dormant within a host cell and can reactivate later. Examples include herpes simplex virus (HSV), varicella-zoster virus (VZV), and HIV.

Q19. Describe what is meant by persistent or chronic viral infection and provide an example:

Background

Topic: Persistent Viral Infections

This question is about infections where the virus remains in the host for a long time, often with ongoing replication.

Key Terms:

  • Persistent infection: Long-term presence of virus in the host.

  • Chronic infection: Continuous, low-level viral replication.

Step-by-Step Guidance

  1. Define persistent or chronic viral infection.

  2. Describe how it differs from acute or latent infections.

  3. Provide an example of a virus that causes this type of infection.

Try solving on your own before revealing the answer!

Final Answer:

A persistent or chronic viral infection is one in which the virus remains in the host for a long period, often with ongoing replication and symptoms. An example is hepatitis B or C virus infection.

Q20. Define prion.

Background

Topic: Unconventional Infectious Agents

This question is about prions, which are infectious proteins that cause disease.

Key Terms:

  • Prion: Infectious protein particle.

Step-by-Step Guidance

  1. Recall what makes prions unique compared to viruses and bacteria.

  2. Think about their composition and how they cause disease.

  3. Formulate a concise definition.

Try solving on your own before revealing the answer!

Final Answer:

A prion is an infectious protein that lacks nucleic acid and causes neurodegenerative diseases.

Q21. Describe the general pathology of prion diseases:

Background

Topic: Prion Diseases

This question is about the effects prions have on the nervous system and how they cause disease.

Key Terms:

  • Neurodegeneration, spongiform changes, amyloid plaques.

Step-by-Step Guidance

  1. Describe what happens to the brain in prion diseases.

  2. Think about the symptoms and microscopic changes observed.

  3. Consider why prion diseases are fatal and untreatable.

Try solving on your own before revealing the answer!

Final Answer:

Prion diseases cause progressive neurodegeneration, characterized by spongiform changes (vacuoles in brain tissue), loss of neurons, and accumulation of abnormal prion protein, leading to fatal brain disorders.

Q22. Name three well-known prion diseases:

Background

Topic: Examples of Prion Diseases

This question is about specific diseases caused by prions in humans and animals.

Key Terms:

  • Creutzfeldt-Jakob disease (CJD), kuru, bovine spongiform encephalopathy (BSE).

Step-by-Step Guidance

  1. List three diseases caused by prions.

  2. Include both human and animal diseases.

  3. Recall common names if possible.

Try solving on your own before revealing the answer!

Final Answer:

  • Creutzfeldt-Jakob disease (CJD)

  • Kuru

  • Bovine spongiform encephalopathy (BSE, "mad cow disease")

Q23. Provide a common name for each of the viruses in the Herpeviridae listed below and name a disease caused by each: HHV1 and HHV2, HHV3, HHV4, HHV5, HHV6/7, HHV8

Background

Topic: Herpesviridae Family

This question is about the human herpesviruses, their common names, and associated diseases.

Key Terms:

  • HHV: Human herpesvirus

  • Diseases: Herpes simplex, chickenpox, mononucleosis, cytomegalovirus infection, roseola, Kaposi's sarcoma

Step-by-Step Guidance

  1. For each HHV number, recall its common name.

  2. List a disease associated with each virus.

  3. Use your knowledge of the Herpesviridae family to match numbers to names and diseases.

Try solving on your own before revealing the answer!

Final Answer:

  • HHV1: Herpes simplex virus type 1 (HSV-1) – oral herpes (cold sores)

  • HHV2: Herpes simplex virus type 2 (HSV-2) – genital herpes

  • HHV3: Varicella-zoster virus (VZV) – chickenpox and shingles

  • HHV4: Epstein-Barr virus (EBV) – infectious mononucleosis

  • HHV5: Cytomegalovirus (CMV) – cytomegalovirus infection

  • HHV6/7: Human herpesvirus 6/7 – roseola (exanthem subitum)

  • HHV8: Kaposi's sarcoma-associated herpesvirus (KSHV) – Kaposi's sarcoma

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