BackMicrobiology Study Guide: Viruses and Prions (Chapter 6)
Study Guide - Smart Notes
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Q1. What argument can be presented to suggest that viruses are not ‘living’?
Background
Topic: Characteristics of Life & Virology
This question tests your understanding of what defines a living organism and how viruses compare to these criteria.
Key Terms:
Virus: A microscopic infectious agent that can only replicate inside the living cells of an organism.
Living organism: Typically defined by characteristics such as metabolism, growth, response to stimuli, and reproduction.
Step-by-Step Guidance
Recall the main characteristics that define living things (e.g., metabolism, cellular structure, ability to reproduce independently).
Consider which of these characteristics viruses possess and which they lack.
Think about how viruses replicate and whether they can do so without a host cell.
Reflect on whether viruses carry out metabolic processes on their own.
Try solving on your own before revealing the answer!
Final Answer:
Viruses are often considered non-living because they lack cellular structure, do not carry out metabolism, and cannot reproduce independently. They require a host cell's machinery to replicate, which means they do not meet all the criteria for life.
Q2. What is meant by host range?
Background
Topic: Virus-Host Interactions
This question is about understanding the specificity of viruses for certain hosts or cell types.
Key Terms:
Host range: The spectrum of host cells a virus can infect.
Tropism: The specificity of a virus for a particular host tissue, determined by host cell receptors and viral surface proteins.
Step-by-Step Guidance
Think about what determines whether a virus can infect a particular organism or cell type.
Consider the role of viral surface proteins and host cell receptors in this process.
Recall examples of viruses with narrow versus broad host ranges.
Try solving on your own before revealing the answer!
Final Answer:
Host range refers to the variety of host species or cell types that a virus can infect. It is determined by the compatibility between viral surface proteins and host cell receptors.
Q3. What is a bacteriophage?
Background
Topic: Types of Viruses
This question focuses on viruses that infect bacteria.
Key Terms:
Bacteriophage (phage): A virus that infects and replicates within bacteria.
Step-by-Step Guidance
Recall the definition of a virus and the different types based on host specificity.
Think about the etymology of the term 'bacteriophage' (bacteria-eater).
Consider the role of bacteriophages in microbiology and biotechnology.
Try solving on your own before revealing the answer!
Final Answer:
A bacteriophage is a virus that specifically infects bacteria. The term comes from 'bacteria' and 'phagein' (to eat), reflecting their role in lysing bacterial cells.
Q4. What are components of viral structure? Describe each.
Background
Topic: Viral Morphology
This question tests your knowledge of the basic structural components of viruses and their functions.
Key Terms:
Nucleic acid: Genetic material (DNA or RNA) of the virus.
Capsid: Protein shell that encases the nucleic acid.
Envelope: Lipid membrane derived from the host cell, present in some viruses.
Spikes (peplomers): Glycoprotein projections involved in host cell recognition and attachment.
Step-by-Step Guidance
List the main structural components found in all viruses and those found only in some.
For each component (nucleic acid, capsid, envelope, spikes), briefly describe its structure and function.
Consider which components are essential for all viruses and which are optional.
Try solving on your own before revealing the answer!
Final Answer:
The main components of viral structure are:
Nucleic acid: The genetic material, either DNA or RNA, single- or double-stranded.
Capsid: A protein shell that protects the nucleic acid.
Envelope (in some viruses): A lipid membrane derived from the host cell, surrounding the capsid.
Spikes (peplomers): Glycoprotein projections that help the virus attach to and enter host cells.
Q5. Describe the various shapes (morphology) of viruses
Background
Topic: Viral Morphology
This question is about the different structural forms viruses can take.
Key Terms:
Helical: Rod-shaped viruses with nucleic acid wound in a spiral and surrounded by a capsid.
Icosahedral: Spherical viruses with a capsid arranged in a symmetrical 20-sided shape.
Complex: Viruses with more intricate structures, often seen in bacteriophages.
Step-by-Step Guidance
Identify the three main morphological types of viruses: helical, icosahedral, and complex.
Describe the structure of each type, focusing on the arrangement of the capsid and nucleic acid.
Provide an example of a virus for each morphology (e.g., influenza for helical, adenovirus for icosahedral, T4 phage for complex).
Try solving on your own before revealing the answer!
Final Answer:
Viruses can have:
Helical morphology: Capsid proteins form a spiral around the nucleic acid (e.g., tobacco mosaic virus).
Icosahedral morphology: Capsid forms a symmetrical 20-sided shape (e.g., adenovirus).
Complex morphology: More elaborate structures, often with additional components (e.g., bacteriophage T4).
Q6. Describe enveloped versus naked viruses.
Background
Topic: Viral Structure
This question tests your understanding of the differences between viruses with and without an envelope.
Key Terms:
Enveloped virus: Virus with a lipid membrane surrounding the capsid.
Naked virus: Virus lacking an envelope; only has a capsid surrounding the nucleic acid.
Step-by-Step Guidance
Define what an envelope is and how viruses acquire it.
Contrast the structural differences between enveloped and naked viruses.
Discuss how the presence or absence of an envelope affects viral stability and transmission.
Try solving on your own before revealing the answer!
Final Answer:
Enveloped viruses have a lipid membrane derived from the host cell, which surrounds the capsid. Naked viruses lack this envelope and consist only of nucleic acid and capsid. Enveloped viruses are generally more sensitive to environmental conditions, while naked viruses are more resistant.
Q7. Understand how viruses are named (taxonomy)
Background
Topic: Viral Taxonomy
This question is about the conventions used in naming viruses at different taxonomic levels.
Key Terms:
Family: Ends with -viridae.
Genus: Ends with -virus.
Species/Subspecies: Often denoted by common names or numbers.
Step-by-Step Guidance
Recall the hierarchical structure of viral taxonomy: order, family, genus, species.
Identify the standard suffixes for family and genus names.
Consider how species and subspecies are typically denoted in viral taxonomy.
Try solving on your own before revealing the answer!
Final Answer:
Viral families end with -viridae, genera end with -virus, and species/subspecies are denoted by common names or numbers (e.g., Human immunodeficiency virus 1). This system helps standardize virus classification.
Q8. What four characteristics are used to group viruses?
Background
Topic: Viral Classification
This question tests your knowledge of the main criteria used to classify viruses.
Key Terms:
Genetic material (DNA or RNA)
Capsid symmetry
Presence or absence of envelope
Host range
Step-by-Step Guidance
List the main features that can vary among viruses and are used for classification.
Think about the type of nucleic acid, structure of the capsid, presence of an envelope, and host specificity.
Consider how these characteristics help virologists group and identify viruses.
Try solving on your own before revealing the answer!
Final Answer:
The four main characteristics used to group viruses are: type of nucleic acid (DNA or RNA), capsid symmetry (helical, icosahedral, complex), presence or absence of an envelope, and host range.
Q9. Why does the inability of viruses to multiply outside of a host cell complicate their detection, enumeration, and identification?
Background
Topic: Viral Cultivation and Detection
This question is about the challenges in working with viruses in the laboratory.
Key Terms:
Obligate intracellular parasite: An organism (like a virus) that can only replicate inside a host cell.
Enumeration: Counting the number of viral particles.
Step-by-Step Guidance
Recall that viruses require living cells to replicate.
Think about how this requirement affects laboratory techniques for detecting and counting viruses.
Consider the limitations of standard microbiological methods (e.g., agar plates) for viruses.
Try solving on your own before revealing the answer!
Final Answer:
Because viruses cannot multiply outside of host cells, they cannot be grown on standard media like bacteria. This makes their detection, enumeration, and identification more complex, often requiring living cells or specialized systems.
Q10. Can we use Koch’s postulates to identify viral diseases?
Background
Topic: Viral Pathogenesis & Microbial Identification
This question explores the limitations of classical microbiological methods for viruses.
Key Terms:
Koch’s postulates: Criteria for establishing a causative relationship between a microbe and a disease.
Obligate intracellular parasite: Viruses require host cells to replicate.
Step-by-Step Guidance
Recall the four Koch’s postulates and their requirements.
Consider whether viruses can be isolated and grown in pure culture.
Think about the challenges in fulfilling each postulate for viruses.
Try solving on your own before revealing the answer!
Final Answer:
Koch’s postulates are difficult to apply to viruses because viruses cannot be grown in pure culture without host cells, and some diseases have no suitable animal model. Modified criteria are often used for viral diseases.
Q11. Describe how viruses can be grown
Background
Topic: Viral Cultivation
This question is about laboratory methods for propagating viruses.
Key Terms:
Embryonated eggs: Fertilized chicken eggs used to grow viruses.
Cell culture: Growing viruses in cultured cells in the lab.
Step-by-Step Guidance
List the main methods used to grow viruses in the laboratory.
Describe how embryonated eggs are used for viral cultivation (e.g., influenza vaccine production).
Explain how cell cultures are prepared and used to propagate viruses.
Try solving on your own before revealing the answer!
Final Answer:
Viruses can be grown in embryonated eggs (by injecting virus into different egg compartments) or in cell cultures (using monolayers of host cells in flasks or plates). These methods provide the living cells viruses need to replicate.
