Study Guide: Viruses, Prions, and Prokaryotes (Bio 101)

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Q1. Why are viruses not considered living things?

Background

Topic: Characteristics of Life

This question tests your understanding of what defines a living organism and why viruses do not meet these criteria.

Key Terms:

Living things: Organisms that exhibit all characteristics of life (such as metabolism, growth, response to stimuli, and reproduction on their own).
Virus: A microscopic infectious agent that can only replicate inside the living cells of an organism.

Step-by-Step Guidance

Recall the main characteristics that define living things (e.g., cellular structure, metabolism, growth, response to environment, reproduction).
Consider which of these characteristics viruses possess and which they lack.
Think about how viruses reproduce and whether they can do so independently.
Reflect on whether viruses have cellular structures or metabolic processes.

Try solving on your own before revealing the answer!

Final Answer:

Viruses are not considered living things because they lack many characteristics of life. Specifically, they do not have a cellular structure, cannot carry out metabolism on their own, and cannot reproduce independently—they require a host cell to replicate. Therefore, they do not meet the criteria for life.

Q2. What are the two basic structural parts of a virus?

Background

Topic: Viral Structure

This question tests your knowledge of the fundamental components that make up all viruses.

Key Terms:

Capsid: The protein shell that surrounds the viral genome.
Genome: The genetic material (DNA or RNA) inside the virus.

Step-by-Step Guidance

Recall the basic structure of a virus and what all viruses have in common.
Identify the part that contains the genetic information.
Identify the protective layer that surrounds the genetic material.
Optional: Think about how you would draw these two parts (a simple circle for the capsid with a strand inside for the genome).

Try solving on your own before revealing the answer!

Final Answer:

The two basic structural parts of a virus are the capsid (protein coat) and the genome (nucleic acid, which can be DNA or RNA). The capsid surrounds and protects the viral genome.

Q3. If you are swimming in a lake with fish that are infected with a virus, why would it be very unlikely that you would get sick?

Background

Topic: Host Specificity of Viruses

This question tests your understanding of how viruses infect specific hosts and why cross-species infection is rare.

Key Terms:

Host specificity: The tendency of a virus to infect only certain species or cell types.
Viral receptors: Molecules on the surface of host cells that viruses must bind to in order to infect the cell.

Step-by-Step Guidance

Consider how viruses recognize and enter host cells.
Think about whether the receptors on fish cells are the same as those on human cells.
Reflect on why most viruses cannot infect organisms outside their usual host range.
Consider what would need to happen for a fish virus to infect a human.

Try solving on your own before revealing the answer!

Final Answer:

It is very unlikely you would get sick because viruses are usually highly specific to their host species. Fish viruses typically cannot infect human cells because they do not recognize or bind to human cell receptors. Therefore, cross-species infection is rare.

Q4. What kinds of nucleic acids can you find in a virus (the genome)?

Background

Topic: Viral Genomes

This question tests your knowledge of the types of genetic material that viruses can have.

Key Terms:

DNA (deoxyribonucleic acid): Double- or single-stranded genetic material.
RNA (ribonucleic acid): Double- or single-stranded genetic material.

Step-by-Step Guidance

Recall that viruses can have either DNA or RNA as their genetic material.
Think about whether these nucleic acids can be single-stranded or double-stranded.
Consider examples of viruses with each type of genome.

Try solving on your own before revealing the answer!

Final Answer:

Viruses can have DNA or RNA as their genome, and each can be either single-stranded or double-stranded. This means there are four possibilities: double-stranded DNA, single-stranded DNA, double-stranded RNA, or single-stranded RNA.

Q5. Describe how a virus infects a host cell (step by step).

Background

Topic: Viral Infection Cycle

This question tests your understanding of the general steps a virus takes to infect and replicate within a host cell.

Key Terms:

Attachment: Virus binds to host cell surface.
Entry: Virus or its genetic material enters the host cell.
Replication: Viral genome is copied.
Assembly: New viral particles are put together.
Release: New viruses exit the host cell.

Step-by-Step Guidance

Start by identifying how the virus recognizes and attaches to the host cell.
Describe how the virus or its genome enters the host cell.
Explain what happens to the viral genome once inside the cell (replication and expression).
Think about how new viral particles are assembled and released from the host cell.

Try solving on your own before revealing the answer!

Final Answer:

The general steps are: (1) Attachment to the host cell, (2) Entry of the viral genome, (3) Replication and synthesis of viral components, (4) Assembly of new viruses, and (5) Release of new viruses from the host cell. These steps allow the virus to hijack the host's machinery to make more viruses.

Q6. What is a prion? Explain as if you are explaining to somebody who has never taken this class.

Background

Topic: Infectious Agents

This question tests your ability to explain what prions are in simple terms.

Key Terms:

Prion: An infectious protein that can cause disease.
Protein: A molecule made of amino acids that performs various functions in cells.

Step-by-Step Guidance

Start by defining what a prion is in basic terms.
Explain how prions differ from other infectious agents like bacteria and viruses.
Describe what makes prions unique (they are just proteins, not living organisms).

Try solving on your own before revealing the answer!

Final Answer:

A prion is a misfolded protein that can cause other normal proteins in the brain to also misfold, leading to disease. Unlike bacteria or viruses, prions do not contain DNA or RNA—they are just proteins.

Q7. How do prions work? Include what they do to the host’s normal proteins in your response.

Background

Topic: Mechanism of Prion Diseases

This question tests your understanding of how prions cause disease at the molecular level.

Key Terms:

Misfolding: When a protein does not fold into its normal shape.
Aggregation: Clumping together of misfolded proteins.

Step-by-Step Guidance

Recall that prions are misfolded proteins.
Explain how a prion interacts with normal proteins in the host.
Describe what happens to the normal proteins after contact with a prion.
Think about the consequences of having many misfolded proteins in the brain.

Try solving on your own before revealing the answer!

Final Answer:

Prions cause disease by inducing normal proteins in the host to change their shape (misfold) into the abnormal prion form. These misfolded proteins then aggregate, forming clumps that damage brain tissue and lead to disease symptoms.

Q8. What are a couple of examples of prion-caused diseases?

Background

Topic: Prion Diseases

This question tests your ability to recall specific diseases caused by prions.

Key Terms:

Prion disease: A disease caused by infectious prion proteins.

Step-by-Step Guidance

Think about diseases in humans and animals that are associated with prions.
Recall any famous outbreaks or cases discussed in class or the textbook.
List at least two examples, one in humans and one in animals if possible.

Try solving on your own before revealing the answer!

Final Answer:

Examples of prion-caused diseases include Creutzfeldt-Jakob disease (CJD) in humans and mad cow disease (bovine spongiform encephalopathy) in cattle. Another example is scrapie in sheep.

Q9. What are the two domains of prokaryotes, and how do they differ from each other?

Background

Topic: Classification of Life

This question tests your understanding of the major groups of prokaryotes and their differences.

Key Terms:

Bacteria: One domain of prokaryotes.
Archaea: The other domain of prokaryotes.
Prokaryote: An organism without a nucleus.

Step-by-Step Guidance

Recall the three domains of life and which two are prokaryotic.
List the two domains of prokaryotes.
Think about key differences between Bacteria and Archaea (e.g., cell wall composition, environments they live in, genetic differences).
Summarize one or two main differences between the two domains.

Try solving on your own before revealing the answer!

Final Answer:

The two domains of prokaryotes are Bacteria and Archaea. They differ in cell wall composition (Bacteria have peptidoglycan, Archaea do not), membrane lipids, and some aspects of their genetics and biochemistry. Archaea often live in extreme environments.

Q10. Rank from smallest to largest: prokaryotic cell, virus, eukaryotic cell.

Background

Topic: Cell Size Comparison

This question tests your understanding of the relative sizes of different biological entities.

Key Terms:

Virus: Smallest infectious agent.
Prokaryotic cell: Bacteria or Archaea, larger than viruses.
Eukaryotic cell: Cells with a nucleus, largest of the three.

Step-by-Step Guidance

Recall the approximate size ranges for viruses, prokaryotic cells, and eukaryotic cells.
Arrange them in order from smallest to largest based on their typical sizes.
Double-check your order by comparing the size ranges (e.g., viruses are measured in nanometers, cells in micrometers).

Try solving on your own before revealing the answer!

Final Answer:

From smallest to largest: virus < prokaryotic cell < eukaryotic cell.

Q11. Be able to describe the shapes and structures of bacteria. Include in your description of bacterial structures, what each structure does.

Background

Topic: Bacterial Morphology and Structure

This question tests your ability to describe bacterial shapes and the function of their cellular structures.

Key Terms:

Cocci: Spherical bacteria.
Bacilli: Rod-shaped bacteria.
Spirilla: Spiral-shaped bacteria.
Cell wall, plasma membrane, flagella, pili, capsule, nucleoid, plasmid, ribosomes.

Step-by-Step Guidance

List the three main shapes of bacteria (cocci, bacilli, spirilla).
Identify the main structures found in a bacterial cell.
For each structure, briefly describe its function (e.g., cell wall provides support, flagella for movement).
Think about how these structures help bacteria survive and reproduce.

Try solving on your own before revealing the answer!

Final Answer:

Bacteria can be cocci (spherical), bacilli (rod-shaped), or spirilla (spiral-shaped). Key structures include: cell wall (protection and shape), plasma membrane (controls entry/exit), flagella (movement), pili (attachment and DNA transfer), capsule (protection), nucleoid (DNA region), plasmid (extra DNA), and ribosomes (protein synthesis).

Q12. What is the major structure that allows bacteria to move?

Background

Topic: Bacterial Motility

This question tests your knowledge of how bacteria move.

Key Terms:

Flagellum (plural: flagella): A whip-like structure used for movement.

Step-by-Step Guidance

Recall which bacterial structure is responsible for motility.
Think about how this structure works to propel the bacterium.
Consider whether all bacteria have this structure.

Try solving on your own before revealing the answer!

Final Answer:

The major structure that allows bacteria to move is the flagellum (plural: flagella), which acts like a propeller to move the cell through its environment.

Q13. What is the DNA like in a prokaryote? Include its shape, and what a plasmid is in your answer.

Background

Topic: Prokaryotic Genetics

This question tests your understanding of the organization of genetic material in prokaryotes.

Key Terms:

Nucleoid: Region where the main DNA is found.
Plasmid: Small, circular DNA molecule separate from the main chromosome.

Step-by-Step Guidance

Recall the shape of the main DNA molecule in prokaryotes.
Describe where this DNA is located in the cell.
Explain what a plasmid is and how it differs from the main chromosome.
Think about the functions plasmids can provide to bacteria.

Try solving on your own before revealing the answer!

Final Answer:

Prokaryotic DNA is typically a single, circular chromosome located in the nucleoid region. Plasmids are small, circular DNA molecules that exist separately from the main chromosome and often carry genes that provide advantages, such as antibiotic resistance.

Q14. After binary fission, how do the daughter cells compare to the parent?

Background

Topic: Prokaryotic Cell Division

This question tests your understanding of the outcome of binary fission in prokaryotes.

Key Terms:

Binary fission: Asexual reproduction in prokaryotes.
Daughter cells: The two cells produced from division.

Step-by-Step Guidance

Recall the process of binary fission and what happens to the DNA.
Think about whether the daughter cells are genetically identical or different from the parent.
Consider if there are any exceptions or mutations that could occur.

Try solving on your own before revealing the answer!

Final Answer:

After binary fission, the two daughter cells are genetically identical to each other and to the parent cell, except for rare mutations that may occur during DNA replication.

Q15. How quickly do bacteria reproduce? (generally speaking)

Background

Topic: Bacterial Growth

This question tests your knowledge of the typical rate of bacterial reproduction under ideal conditions.

Key Terms:

Generation time: The time it takes for a bacterial population to double.

Step-by-Step Guidance

Recall the typical range of generation times for bacteria in optimal conditions.
Think about how environmental factors can affect reproduction rate.
Consider examples of fast-growing bacteria.

Try solving on your own before revealing the answer!

Final Answer:

Bacteria can reproduce very quickly, with some species doubling in number every 20 minutes under ideal conditions. However, actual rates depend on the environment and resources available.

Q16. Do bacteria reproduce sexually, or asexually? Explain.

Background

Topic: Modes of Reproduction

This question tests your understanding of how bacteria reproduce and whether genetic exchange occurs.

Key Terms:

Asexual reproduction: Offspring arise from a single parent, no fusion of gametes.
Binary fission: Main method of bacterial reproduction.
Genetic exchange: Transfer of DNA between cells (not true sexual reproduction).

Step-by-Step Guidance

Recall the main method by which bacteria reproduce.
Explain why this method is considered asexual.
Consider whether bacteria can exchange genetic material in other ways (e.g., conjugation), and if this counts as sexual reproduction.

Try solving on your own before revealing the answer!

Final Answer:

Bacteria reproduce asexually by binary fission, producing genetically identical offspring. While they can exchange genetic material through processes like conjugation, this is not considered true sexual reproduction because it does not involve gametes or the formation of a new organism from two parents.

Q17. What is the purpose of a sex pilus? How could this relate to antibiotic resistance?

Background

Topic: Bacterial Conjugation and Antibiotic Resistance

This question tests your understanding of the role of the sex pilus in genetic exchange and its implications for antibiotic resistance.

Key Terms:

Sex pilus: A structure used to transfer DNA between bacteria.
Conjugation: The process of DNA transfer via the sex pilus.
Antibiotic resistance: The ability of bacteria to survive antibiotics.

Step-by-Step Guidance

Define what a sex pilus is and its function in bacterial cells.
Explain how the sex pilus is involved in conjugation (DNA transfer).
Consider what types of genes can be transferred via conjugation (e.g., antibiotic resistance genes on plasmids).
Think about how this process can spread antibiotic resistance in bacterial populations.

Try solving on your own before revealing the answer!

Final Answer:

The sex pilus is used by bacteria to connect to another cell and transfer DNA during conjugation. This process can transfer plasmids carrying antibiotic resistance genes, allowing resistance to spread rapidly among bacteria.

Q18. Why are bacteria more able to quickly adapt to their environments (evolve) than multicellular organisms?

Background

Topic: Evolution and Adaptation

This question tests your understanding of the factors that contribute to rapid bacterial evolution.

Key Terms:

Mutation rate: Frequency of genetic changes.
Generation time: Time between cell divisions.
Genetic exchange: Transfer of genes between cells.

Step-by-Step Guidance

Consider how quickly bacteria reproduce compared to multicellular organisms.
Think about the impact of short generation times on evolution.
Recall that bacteria can exchange genes through processes like conjugation, transformation, and transduction.
Reflect on how these factors contribute to rapid adaptation and evolution.

Try solving on your own before revealing the answer!

Final Answer:

Bacteria can adapt quickly because they reproduce rapidly (short generation times), have high mutation rates, and can exchange genes with other bacteria. These factors allow beneficial traits to spread quickly, leading to rapid evolution compared to multicellular organisms.

Definitions: Capsid, Pandemic, Cocci, Bacilli, Plasmid, Binary Fission, Sex Pilus

Background

Topic: Key Terms in Microbiology

This section tests your ability to define important terms related to viruses and prokaryotes.

Key Terms:

Capsid: Protein shell of a virus.
Pandemic: A global outbreak of disease.
Cocci: Spherical bacteria.
Bacilli: Rod-shaped bacteria.
Plasmid: Small, circular DNA in bacteria.
Binary Fission: Asexual reproduction in prokaryotes.
Sex Pilus: Structure for DNA transfer in bacteria.

Step-by-Step Guidance

Write a one-sentence definition for each term.
For structures, mention their function or role in the cell.
For terms like pandemic, relate to disease spread.

Try solving on your own before revealing the answer!

Final Answer:

Capsid: The protein shell that surrounds and protects the genetic material of a virus.
Pandemic: A disease outbreak that spreads across countries or continents, affecting a large number of people.
Cocci: Spherical-shaped bacteria.
Bacilli: Rod-shaped bacteria.
Plasmid: A small, circular DNA molecule in bacteria that can carry extra genes, such as those for antibiotic resistance.
Binary Fission: The process by which prokaryotes reproduce asexually, producing two identical cells.
Sex Pilus: A hair-like appendage used by bacteria to transfer DNA to another cell during conjugation.