BIO2440 Microbiology Study Guide – Step-by-Step Guidance

Q1. Differentiate a virus from a bacterium.

Background

Topic: Viruses vs. Bacteria

This question tests your understanding of the fundamental differences between viruses and bacteria, including their structure, replication, and classification.

Key Terms:

• Virus: A non-cellular infectious agent that requires a host cell to replicate.

• Bacterium: A unicellular, prokaryotic microorganism capable of independent life and reproduction.

Step-by-Step Guidance

1. Consider the basic structure of each: viruses lack cellular structure, while bacteria are prokaryotic cells with a cell wall, plasma membrane, and cytoplasm.

2. Think about how each replicates: viruses require a host cell for replication, but bacteria can reproduce independently by binary fission.

3. Reflect on genetic material: viruses may have DNA or RNA, but bacteria always have both DNA and RNA.

4. Consider metabolic activity: bacteria carry out metabolism, while viruses do not have metabolic processes outside a host.

Try solving on your own before revealing the answer!

Final Answer:

Viruses are acellular infectious agents that require a host cell to replicate and lack metabolic machinery, while bacteria are unicellular prokaryotes capable of independent metabolism and reproduction. Viruses can have either DNA or RNA as genetic material, but bacteria have both DNA and RNA. Bacteria have cellular structures such as cell walls and plasma membranes; viruses do not.

Q2. How could the small size of viruses have helped researchers detect viruses before the invention of the electron microscope?

Background

Topic: Virus Discovery and Detection

This question explores how the physical properties of viruses, particularly their small size, contributed to their early detection using filtration techniques.

Key Terms:

• Filtration: A method used to separate particles based on size.

• Electron Microscope: An instrument that allows visualization of structures smaller than those visible with light microscopes.

Step-by-Step Guidance

1. Recall that viruses are much smaller than bacteria and can pass through filters that retain bacteria.

2. Think about how early researchers used porcelain or Chamberland filters to separate infectious agents from bacteria.

3. Consider what it meant when infectious material passed through a filter that should have removed all bacteria.

4. Reflect on how this observation led to the hypothesis of a new, smaller infectious agent—what we now call viruses.

Try solving on your own before revealing the answer!

Final Answer:

The small size of viruses allowed them to pass through filters that trapped bacteria, enabling researchers to detect their presence by observing infectious activity in the filtrate. This filtration evidence suggested the existence of infectious agents smaller than bacteria, leading to the discovery of viruses before electron microscopes were available.

Q3. Describe the chemical and physical structure of both an enveloped and a nonenveloped virus.

Background

Topic: Viral Structure

This question tests your knowledge of the basic components and differences between enveloped and nonenveloped viruses.

Key Terms:

• Capsid: Protein coat surrounding the viral genome.

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

• Spikes: Glycoprotein projections on the surface of some viruses.

Step-by-Step Guidance

1. Start by describing the core structure common to all viruses: the nucleic acid genome (DNA or RNA) and the protein capsid.

2. For nonenveloped viruses, focus on the capsid's shape (e.g., polyhedral, helical) and the presence of surface proteins or spikes.

3. For enveloped viruses, add the presence of a lipid bilayer envelope surrounding the capsid, often with embedded glycoprotein spikes.

4. Consider how the envelope is acquired (from the host cell membrane) and how it affects viral entry and immune evasion.

Try solving on your own before revealing the answer!

Final Answer:

Nonenveloped viruses consist of a nucleic acid genome enclosed in a protein capsid, sometimes with surface spikes. Enveloped viruses have a similar core but are surrounded by a lipid envelope derived from the host cell membrane, with embedded glycoprotein spikes. The envelope aids in host cell entry and immune evasion.

Q4. Diagram a nonenveloped polyhedral virus that has spikes.

Background

Topic: Viral Morphology

This question asks you to visualize and represent the structure of a nonenveloped polyhedral virus, emphasizing the arrangement of spikes.

Key Terms:

• Polyhedral Virus: A virus with a many-sided (often icosahedral) capsid.

• Spikes: Protein projections that extend from the capsid surface.

Step-by-Step Guidance

1. Draw a geometric shape representing the polyhedral capsid (commonly an icosahedron).

2. Indicate the presence of the viral genome inside the capsid.

3. Add spikes (protein projections) extending from the vertices or faces of the polyhedral capsid.

4. Label the capsid, spikes, and genome in your diagram.

Try solving on your own before revealing the answer!

Final Answer:

A nonenveloped polyhedral virus can be represented as an icosahedral (20-sided) structure with protein spikes protruding from its surface. The genome is enclosed within the capsid. Spikes are shown as short projections at the vertices or faces of the polyhedron.

Q5. Define viral species. How does a virus species differ from a bacterial species?

Background

Topic: Viral Taxonomy

This question examines your understanding of how viruses are classified and how their species concept differs from that of bacteria.

Key Terms:

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

• Bacterial Species: A group of bacteria with similar characteristics that can reproduce by binary fission.

Step-by-Step Guidance

1. Define what constitutes a viral species according to the International Committee on Taxonomy of Viruses (ICTV).

2. Describe how viral species are grouped based on genetic similarity and host range, rather than reproductive compatibility.

3. Contrast this with bacterial species, which are defined by phenotypic and genetic similarity and the ability to reproduce independently.

4. Consider why viruses cannot be classified by reproductive compatibility, as they do not reproduce sexually or by binary fission.

Try solving on your own before revealing the answer!

Final Answer:

A viral species is a group of viruses with the same genetic information and ecological niche. Unlike bacterial species, which are defined by the ability to reproduce and share genetic and phenotypic traits, viral species are classified based on genetic similarity and host range, since viruses do not reproduce independently.