Microbiology Study Guide: Viruses (Chapter 13)

Q1. Define a virus.

Background

Topic: Virology - Virus Definition

This question tests your understanding of what constitutes a virus and how it differs from other microorganisms.

Key Terms

• Virus: A microscopic infectious agent that requires a host cell to replicate.

• Obligate intracellular parasite: An organism that can only reproduce inside the cells of a host organism.

Step-by-Step Guidance

1. Consider what makes viruses unique compared to bacteria, fungi, and other microbes.

2. Think about whether viruses are considered living or non-living, and why.

3. Identify the basic structural and functional characteristics that all viruses share.

4. Reflect on the requirement for a host cell in the viral life cycle.

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Q2. Identify common structures associated with viruses.

Background

Topic: Viral Structure

This question focuses on the physical components that make up a virus particle (virion).

Key Terms

• Capsid: Protein shell that encloses the viral genome.

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

• Nucleic acid: Genetic material (DNA or RNA) inside the virus.

• Spikes (glycoproteins): Surface proteins involved in host cell attachment.

Step-by-Step Guidance

1. List the main components found in all viruses.

2. Identify which structures are optional (present in some, but not all, viruses).

3. Consider the function of each structure in the viral life cycle.

4. Think about how these structures help viruses infect host cells.

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Q3. Diagram the bacteriophage lytic replication cycle.

Background

Topic: Bacteriophage Life Cycles

This question asks you to outline the steps a bacteriophage (virus that infects bacteria) takes to replicate via the lytic cycle.

Key Terms

• Lytic cycle: Viral replication process resulting in destruction of the host cell.

• Bacteriophage: Virus that infects bacteria.

Step-by-Step Guidance

1. Recall the main stages of the lytic cycle (e.g., attachment, penetration, etc.).

2. For each stage, briefly describe what happens to the phage and the host cell.

3. Think about how the viral genome is replicated and new virions are assembled.

4. Consider what happens to the host cell at the end of the cycle.

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Q4. Differentiate between the lytic replication cycle and lysogeny.

Background

Topic: Bacteriophage Life Cycles

This question tests your understanding of the two main types of bacteriophage replication cycles: lytic and lysogenic.

Key Terms

• Lytic cycle: Immediate replication and destruction of the host cell.

• Lysogeny: Viral genome integrates into the host genome and replicates passively.

• Prophage: Phage DNA integrated into the bacterial chromosome.

Step-by-Step Guidance

1. Define the lytic cycle and its outcome for the host cell.

2. Define lysogeny and explain how it differs in terms of viral replication and host cell fate.

3. Identify the conditions under which a lysogenic phage might enter the lytic cycle.

4. Compare the advantages and disadvantages of each cycle for the virus.

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Q5. Explain the term phage conversion.

Background

Topic: Bacteriophage Genetics

This question is about how bacteriophages can alter the phenotype of their bacterial hosts.

Key Terms

• Phage conversion (lysogenic conversion): When a bacterium acquires new traits due to the presence of a prophage.

• Prophage: Phage DNA integrated into the bacterial genome.

Step-by-Step Guidance

1. Define what happens during lysogeny at the genetic level.

2. Consider how the presence of phage genes can affect bacterial properties.

3. Think of examples where phage conversion leads to increased virulence in bacteria.

4. Reflect on the significance of this process in bacterial evolution and disease.

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