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' and what it implies about its function.
Consider the importance 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 infecting and often 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 encloses 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 or some viruses.
For each component (nucleic acid, capsid, envelope, spikes), briefly describe its structure and function.
Note which components are present in all viruses and which are only in some.
Try solving on your own before revealing the answer!
Final Answer:
The main components of viral structure are:
Nucleic acid: The genetic material, which can be 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 including additional components like tails or complex outer walls.
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, if possible.
Try solving on your own before revealing the answer!
Final Answer:
Helical: The capsid forms a spiral around the nucleic acid, creating a rod-like shape (e.g., tobacco mosaic virus).
Icosahedral: The capsid forms a symmetrical, 20-sided structure (e.g., adenovirus).
Complex: These viruses have more elaborate structures, such as bacteriophages with head and tail components.
Q6. Describe enveloped versus naked viruses.
Background
Topic: Viral Structure
This question focuses on the presence or absence of a lipid envelope in viruses and the implications for their biology.
Key Terms:
Enveloped virus: A virus with a lipid membrane surrounding its capsid.
Naked virus: A virus lacking an envelope, consisting only of nucleic acid and capsid.
Step-by-Step Guidance
Define what an envelope is and how viruses acquire it.
Contrast the structural differences between enveloped and naked viruses.
Consider 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 and classifying viruses.
Key Terms:
Family: The highest taxonomic group for viruses, ending in -viridae.
Genus: The next level, ending in -virus.
Species/Subspecies: Specific viruses, often named for the disease or location associated with them.
Step-by-Step Guidance
Recall the hierarchical structure of viral taxonomy: family, genus, species, subspecies.
Identify the standard suffixes for family and genus names.
Consider how species and subspecies are denoted in viral nomenclature.
Try solving on your own before revealing the answer!
Final Answer:
Family names end with -viridae (e.g., Herpesviridae).
Genus names end with -virus (e.g., Simplexvirus).
Species and subspecies are often named for the disease they cause or the location where they were discovered (e.g., Human herpesvirus 1).
Q8. What four characteristics are used to group viruses?
Background
Topic: Viral Classification
This question is about the main criteria used to classify viruses into groups.
Key Terms:
Nucleic acid type (DNA or RNA)
Capsid symmetry (helical, icosahedral, complex)
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 genetic material, structure, and host specificity.
Recall how these features help group viruses into families and genera.
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
Host range (which organisms or cells they infect)
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.
Detection/enumeration: Methods used to find and count viruses.
Step-by-Step Guidance
Recall that viruses cannot replicate on their own and require host cells.
Think about how this affects the ability to grow viruses in the lab compared to bacteria.
Consider the implications for detecting and counting viruses in samples.
Try solving on your own before revealing the answer!
Final Answer:
Because viruses cannot multiply outside of a host cell, they cannot be grown on standard laboratory media like bacteria. This makes their detection, enumeration, and identification more complex, often requiring living cells or specialized systems for cultivation.
Q10. Can we use Koch’s postulates to identify viral diseases?
Background
Topic: Viral Pathogenesis & Disease Identification
This question is about the limitations of classical microbiological methods for viruses.
Key Terms:
Koch’s postulates: A set of criteria used to establish a causative relationship between a microbe and a disease.
Viral diseases: Diseases caused by viruses, which may not always fulfill Koch’s postulates.
Step-by-Step Guidance
Recall the four Koch’s postulates and their requirements.
Consider the unique properties of viruses (e.g., need for host cells, inability to grow on standard media).
Think about whether all postulates can be fulfilled for viral diseases.
Try solving on your own before revealing the answer!
Final Answer:
Koch’s postulates are often difficult or impossible to apply to viruses because viruses cannot be grown in pure culture without host cells, and some diseases do not have suitable animal models. Modified criteria are sometimes used for viral diseases.
Q11. Describe how viruses can be grown
Background
Topic: Viral Cultivation
This question is about the laboratory methods used to propagate viruses for study.
Key Terms:
Embryonated eggs: Fertilized chicken eggs used as a growth medium for viruses.
Cell culture: Growing viruses in cultured animal or plant cells.
Step-by-Step Guidance
List the main methods used to grow viruses in the lab (e.g., embryonated eggs, cell culture).
Describe how each method provides living cells for viral replication.
Consider the advantages and limitations of each method.
Try solving on your own before revealing the answer!
Final Answer:
Embryonated eggs: Viruses are injected into specific sites of fertilized eggs, allowing them to replicate in the developing tissues.
Cell culture: Viruses are grown in monolayers of cultured cells, which provide the necessary environment for replication.
