Microbiology Study Guide: Viruses and Prions

Q1. What are the characteristics of viruses?

Background

Topic: Viral Structure and Properties

This question tests your understanding of what makes viruses unique compared to other microorganisms, focusing on their structure, replication, and basic properties.

Key Terms:

• Virus: A non-cellular infectious agent with genetic material (DNA or RNA) surrounded by a protein coat.

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

• Capsid: Protein shell enclosing the viral genome.

• Envelope: Some viruses have a lipid membrane derived from the host cell.

Step-by-Step Guidance

1. List the basic structural components of a virus (e.g., genetic material, capsid, envelope).

2. Describe how viruses differ from living cells in terms of metabolism and replication.

3. Explain why viruses are considered obligate intracellular parasites.

4. Consider the size and filterability of viruses compared to bacteria.

Try summarizing the main characteristics before checking the answer!

Q2. How do viruses compare to bacteria?

Background

Topic: Viruses vs. Bacteria

This question asks you to compare and contrast the fundamental differences between viruses and bacteria, two major types of infectious agents.

Key Terms:

• Prokaryote: Bacteria are single-celled organisms without a nucleus.

• Virus: Acellular, non-living infectious agent.

• Replication: Bacteria reproduce by binary fission; viruses require host cells.

Step-by-Step Guidance

1. Identify the main structural differences (cellular vs. acellular, presence of organelles, etc.).

2. Compare their methods of reproduction.

3. Discuss their response to antibiotics and why viruses are not affected.

4. Consider their size and genetic material differences.

Try outlining the differences before revealing the answer!

Q3. What determines the virus host range?

Background

Topic: Viral Host Specificity

This question focuses on the factors that limit or define which organisms or cells a virus can infect.

Key Terms:

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

• Receptor: Specific molecules on the host cell surface that viruses recognize and bind to.

• Cellular factors: Internal host cell machinery compatibility.

Step-by-Step Guidance

1. Explain the role of viral attachment proteins and host cell receptors.

2. Discuss how compatibility between viral and host cell machinery affects infection.

3. Consider examples of viruses with narrow vs. broad host ranges.

Think about what limits a virus to certain hosts before checking the answer!

Q4. What is a virion?

Background

Topic: Viral Structure

This question asks you to define the term 'virion' and understand its significance in the viral life cycle.

Key Terms:

• Virion: A complete, infectious viral particle outside a host cell.

• Capsid: Protein coat surrounding the genome.

• Envelope: Lipid membrane present in some virions.

Step-by-Step Guidance

1. Define 'virion' in your own words.

2. List the main components of a virion.

3. Explain the difference between a virion and a virus inside a host cell.

Try defining 'virion' before revealing the answer!

Q5. How are viruses classified?

Background

Topic: Viral Taxonomy

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

Key Terms:

• Genome type: DNA or RNA, single- or double-stranded.

• Capsid symmetry: Helical, icosahedral, or complex.

• Envelope presence: Enveloped or non-enveloped.

Step-by-Step Guidance

1. List the main criteria used for viral classification (genetic material, structure, etc.).

2. Describe how these criteria are used to group viruses into families and genera.

3. Consider examples of classification systems (e.g., Baltimore classification).

Try listing classification criteria before checking the answer!

Q6. Why must viruses be grown in living cells for culturing?

Background

Topic: Viral Cultivation

This question explores why viruses cannot be cultured on standard laboratory media like bacteria.

Key Terms:

• Obligate intracellular parasite: Viruses require host cell machinery to replicate.

• Cell culture: Growing cells in vitro for viral propagation.

Step-by-Step Guidance

1. Explain why viruses cannot replicate independently.

2. Describe the role of host cells in viral replication.

3. List common methods for culturing viruses (e.g., animal cells, embryonated eggs, bacterial lawns for bacteriophages).

Think about why viruses need living cells before checking the answer!

Q7. What methods are used to identify viruses?

Background

Topic: Viral Identification

This question asks you to describe laboratory techniques used to detect and identify viruses.

Key Terms:

• Serology: Detection of viral antigens or antibodies.

• Molecular methods: PCR, nucleic acid hybridization.

• Electron microscopy: Visualization of viral particles.

Step-by-Step Guidance

1. List common laboratory methods for viral identification.

2. Briefly describe how each method works (e.g., PCR amplifies viral genetic material).

3. Consider the advantages and limitations of each method.

Try listing identification methods before checking the answer!

Q8. Compare the lytic and lysogenic cycles.

Background

Topic: Bacteriophage Life Cycles

This question tests your understanding of the two main replication strategies of bacteriophages (viruses that infect bacteria).

Key Terms:

• Lytic cycle: Viral replication resulting in host cell lysis and release of new virions.

• Lysogenic cycle: Viral genome integrates into host DNA and replicates with it without killing the host immediately.

• Prophage: Integrated viral DNA in the bacterial genome.

Step-by-Step Guidance

1. Describe the main steps of the lytic cycle (attachment, penetration, biosynthesis, maturation, release).

2. Outline the lysogenic cycle, focusing on integration and replication with the host genome.

3. Compare the outcomes for the host cell in each cycle.

Try outlining the differences before checking the answer!

Q9. How does lysogeny influence the evolution of bacteria?

Background

Topic: Lysogeny and Bacterial Evolution

This question explores how the integration of viral DNA (prophage) can affect bacterial genetics and evolution.

Key Terms:

• Lysogeny: Integration of phage DNA into bacterial chromosome.

• Prophage: Dormant phage DNA in the host genome.

• Lysogenic conversion: Acquisition of new traits by bacteria due to prophage genes.

Step-by-Step Guidance

1. Explain how prophage genes can alter bacterial phenotype (e.g., toxin production).

2. Discuss the role of lysogeny in horizontal gene transfer.

3. Consider examples of bacterial traits acquired through lysogenic conversion.

Think about how viral DNA can benefit bacteria before checking the answer!

Q10. What is the difference between DNA and RNA viruses?

Background

Topic: Viral Genome Types

This question asks you to compare viruses based on the type of nucleic acid they contain and how this affects their replication.

Key Terms:

• DNA virus: Contains DNA as genetic material.

• RNA virus: Contains RNA as genetic material.

• Replication: DNA viruses often replicate in the nucleus; RNA viruses usually replicate in the cytoplasm.

Step-by-Step Guidance

1. List the main differences in genetic material (DNA vs. RNA, single- or double-stranded).

2. Describe how replication strategies differ between DNA and RNA viruses.

3. Consider examples of each type of virus.

Try comparing the two types before checking the answer!

Q11. What are the characteristics of prions?

Background

Topic: Prions

This question tests your understanding of prions, which are infectious proteins distinct from viruses and bacteria.

Key Terms:

• Prion: Infectious protein particle lacking nucleic acid.

• Protein misfolding: Prions cause normal proteins to misfold.

• Diseases: Prions cause neurodegenerative diseases (e.g., Creutzfeldt-Jakob disease).

Step-by-Step Guidance

1. Define what a prion is and how it differs from viruses and bacteria.

2. Describe how prions propagate in the host.

3. List diseases associated with prions.

Try listing prion characteristics before checking the answer!