Exam 2

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, which are two major types of microorganisms studied in microbiology.

Key Terms:

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

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

Step-by-Step Guidance

1. Consider the structural differences: Think about whether each has a cell wall, cell membrane, cytoplasm, and genetic material.

2. Reflect on their replication: Ask yourself if either can reproduce independently or if one requires a host cell.

3. Think about their size and visibility: Which can be seen with a light microscope, and which typically requires an electron microscope?

4. Consider their response to antibiotics: Do both respond to antibiotics in the same way?

Try solving on your own before revealing the answer!

Final Answer:

Viruses are acellular, much smaller than bacteria, and require a host cell to replicate; they lack cellular structures such as a cell wall, cytoplasm, and ribosomes. Bacteria are unicellular prokaryotes that can reproduce independently, have a cell wall, and can be treated with antibiotics, unlike viruses.

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

Background

Topic: Virus Detection and Size

This question explores how the physical properties of viruses, particularly their small size, influenced early virology research methods.

Key Terms:

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

• Electron Microscope: An instrument that allows visualization of very small particles, such as viruses.

Step-by-Step Guidance

1. Recall what types of filters were available to early researchers and what they could separate.

2. Think about what would happen if a solution containing both bacteria and viruses was passed through a filter with very small pores.

3. Consider what researchers might observe in the filtrate after filtering out bacteria.

4. Reflect on how the presence of infectious material in the filtrate could suggest the existence of something smaller than bacteria.

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. Researchers noticed that the filtrate could still cause disease, indicating the presence of infectious agents smaller than bacteria, even before viruses could be seen with an electron microscope.

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 surrounding some viruses, derived from the host cell membrane.

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

Step-by-Step Guidance

1. Identify the basic components all viruses share (nucleic acid and capsid).

2. Describe what additional structure enveloped viruses have compared to nonenveloped viruses.

3. Explain the function and composition of the envelope and spikes.

4. Think about how these structures affect the virus's ability to infect host cells and survive outside the host.

Try solving on your own before revealing the answer!

Final Answer:

Nonenveloped viruses consist of nucleic acid (DNA or RNA) surrounded by a protein capsid. Enveloped viruses have an additional lipid bilayer envelope, often with glycoprotein spikes, surrounding the capsid. The envelope is derived from the host cell membrane and helps the virus enter host cells.

Q4. Diagram a nonenveloped polyhedral virus that has spikes.

Background

Topic: Viral Morphology

This question asks you to visualize and draw the structure of a specific type of virus, reinforcing your understanding of viral shapes and surface features.

Key Terms:

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

• Spikes: Protein structures that protrude from the capsid.

Step-by-Step Guidance

1. Recall the typical shape of a polyhedral virus (often icosahedral).

2. Draw a geometric shape (like a soccer ball) to represent the capsid.

3. Add short projections (spikes) extending from the vertices or faces of the polyhedron.

4. Label the nucleic acid inside, the capsid, and the spikes.

Try solving on your own before revealing the answer!

Final Answer:

A nonenveloped polyhedral virus can be drawn as an icosahedron (20-sided figure) with protein spikes protruding from its surface. The nucleic acid is enclosed within the capsid, and the spikes help the virus attach to host cells.

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

Background

Topic: Microbial Taxonomy

This question examines your understanding of how viruses are classified and how this differs from the classification 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. Recall the definition of a species for both viruses and bacteria.

2. Think about how viruses replicate compared to bacteria.

3. Consider why the concept of species is different for viruses (which do not reproduce sexually or asexually in the same way as bacteria).

4. Reflect on the criteria used to group viruses into species (genetic similarity, host range, etc.).

Try solving on your own before revealing the answer!

Final Answer:

A viral species is defined as 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 characteristics, viral species are grouped by genetic similarity and host range, since viruses do not reproduce independently.