Microbiology Study Guide: Viruses, Viroids, and Prions

Q1. What are the general characteristics of all viruses?

Background

Topic: Virology Basics

This question tests your understanding of what makes viruses unique compared to other microorganisms, including their structure, replication, and dependence on host cells.

Key Terms:

• Obligate intracellular parasites

• Capsid

• Nucleic acid (DNA or RNA)

• Host specificity

Step-by-Step Guidance

1. List the main features that all viruses share, such as their basic structure and replication requirements.

2. Consider how viruses differ from living cells (e.g., lack of cellular structure, metabolism, or independent reproduction).

3. Think about the types of genetic material viruses can have (DNA or RNA, single- or double-stranded).

4. Reflect on the importance of the capsid and, in some cases, an envelope.

Try summarizing these characteristics before checking the answer!

Final Answer:

All viruses are acellular, obligate intracellular parasites composed of genetic material (either DNA or RNA) surrounded by a protein coat called a capsid. Some have an additional lipid envelope. They cannot carry out metabolism or reproduce independently, relying entirely on host cells for replication.

Q2. What are the six characteristics in which viruses differ?

Background

Topic: Viral Diversity

This question asks you to identify the main ways in which viruses can be classified or distinguished from one another.

Key Terms:

• Genome type (DNA or RNA, single- or double-stranded)

• Capsid symmetry

• Presence or absence of envelope

• Host range

• Size and shape

• Replication strategy

Step-by-Step Guidance

1. Recall the different types of viral genomes and how they affect classification.

2. Think about the physical structure of viruses, including capsid shape and presence of an envelope.

3. Consider how viruses differ in the hosts they infect and their replication cycles.

4. List out six distinct characteristics based on your textbook or lecture notes.

Try listing all six characteristics before checking the answer!

Final Answer:

The six characteristics include: type of nucleic acid, strandedness, capsid symmetry, presence or absence of envelope, host range, and replication strategy.

Q3. Describe the lytic replication cycle of bacteriophage T4.

Background

Topic: Bacteriophage Life Cycles

This question focuses on the steps involved in the lytic cycle, where a bacteriophage infects a bacterial cell and leads to its destruction.

Key Terms:

• Attachment

• Penetration

• Synthesis

• Assembly

• Release

Step-by-Step Guidance

1. Identify and describe each stage of the lytic cycle in order.

2. Explain what happens to the host cell at each stage.

3. Consider how the phage uses the host's machinery for replication.

4. Think about the outcome for the bacterial cell at the end of the cycle.

Try outlining the steps before checking the answer!

Final Answer:

The lytic cycle includes: attachment, penetration, synthesis of viral components, assembly of new virions, and release (lysis) of the host cell.

Q4. How do you interpret a graph of burst time and burst size?

Background

Topic: Bacteriophage Replication Kinetics

This question tests your ability to analyze data from experiments measuring the timing and quantity of virus release from infected cells.

Key Terms:

• Burst time: time from infection to cell lysis

• Burst size: number of virions released per cell

Step-by-Step Guidance

1. Examine the axes of the graph to determine what is being measured (e.g., time vs. number of virions).

2. Identify the point at which the number of virions increases sharply (indicating lysis).

3. Determine the burst time by finding the time interval between infection and the start of virion release.

4. Estimate the burst size by looking at the plateau value after lysis.

Try interpreting a sample graph before checking the answer!

Final Answer:

Burst time is the interval from infection to lysis, and burst size is the number of virions released per lysed cell, shown by the plateau on the graph.

Q5. Describe the lysogenic replication cycle of bacteriophage lambda.

Background

Topic: Lysogeny in Bacteriophages

This question focuses on the alternative replication cycle where the phage genome integrates into the host genome and remains dormant.

Key Terms:

• Prophage

• Lysogeny

• Induction

• Integration

Step-by-Step Guidance

1. List the steps of the lysogenic cycle, starting with attachment and entry.

2. Describe how the phage DNA integrates into the host chromosome.

3. Explain what happens during the lysogenic state and how the prophage is replicated.

4. Discuss what can trigger induction and entry into the lytic cycle.

Try outlining the lysogenic cycle before checking the answer!

Final Answer:

The lysogenic cycle involves integration of phage DNA into the host genome (prophage), replication with the host, and possible induction into the lytic cycle.

Q6. What are three mechanisms of animal virus attachment and entry?

Background

Topic: Animal Virus Infection

This question asks you to describe how animal viruses attach to and enter host cells.

Key Terms:

• Direct penetration

• Membrane fusion

• Endocytosis

Step-by-Step Guidance

1. Identify the three main mechanisms by which animal viruses enter host cells.

2. Briefly describe each mechanism and the types of viruses that use them.

3. Consider how the presence or absence of an envelope affects entry.

Try describing each mechanism before checking the answer!

Final Answer:

The three mechanisms are direct penetration, membrane fusion (for enveloped viruses), and endocytosis.

Q7. How do the replication and synthesis processes differ among dsDNA, ssDNA, ssRNA+, ssRNA-, retroviruses, and dsRNA viruses?

Background

Topic: Viral Genome Replication Strategies

This question tests your understanding of how different types of viral genomes are replicated and expressed in host cells.

Key Terms:

• dsDNA: double-stranded DNA

• ssDNA: single-stranded DNA

• ssRNA+: positive-sense single-stranded RNA

• ssRNA-: negative-sense single-stranded RNA

• Retrovirus: RNA virus with reverse transcription

• dsRNA: double-stranded RNA

Step-by-Step Guidance

1. For each genome type, recall where replication occurs (nucleus or cytoplasm) and what enzymes are required.

2. Describe how mRNA is produced for each type (e.g., direct use, transcription, reverse transcription).

3. Note any unique steps, such as reverse transcription in retroviruses.

4. Compare and contrast the synthesis processes among the different types.

Try summarizing the differences before checking the answer!

Final Answer:

Each genome type uses different strategies: dsDNA viruses use host or viral polymerases, ssDNA viruses must synthesize a complementary strand, ssRNA+ can serve as mRNA, ssRNA- must be transcribed to mRNA, retroviruses use reverse transcriptase, and dsRNA viruses require RNA-dependent RNA polymerase.

Q8. What is a persistent infection?

Background

Topic: Viral Pathogenesis

This question asks you to define and explain infections where the virus remains in the host for extended periods.

Key Terms:

• Chronic infection

• Latent infection

• Slow infection

Step-by-Step Guidance

1. Define what makes an infection 'persistent' compared to acute infections.

2. Describe the possible outcomes for the host and the virus.

3. Give examples of persistent infections if possible.

Try defining persistent infection before checking the answer!

Final Answer:

A persistent infection is one in which the virus remains in the host for long periods, often with ongoing or intermittent production of new virions.

Q9. What is the difference between latency in animal viruses and bacteriophages?

Background

Topic: Viral Latency

This question compares how viruses remain dormant in animal cells versus bacterial cells.

Key Terms:

• Latency (animal viruses)

• Lysogeny (bacteriophages)

• Provirus

• Prophage

Step-by-Step Guidance

1. Define latency in the context of animal viruses and lysogeny in bacteriophages.

2. Describe how the viral genome is maintained in each case (integrated or episomal).

3. Explain how reactivation or induction can occur.

4. Compare the permanence of integration in animal viruses versus bacteriophages.

Try comparing the two forms of latency before checking the answer!

Final Answer:

Latency in animal viruses can involve integration as a provirus or episomal maintenance, while lysogeny in bacteriophages involves integration as a prophage; proviruses may be permanent, while prophages can be excised.

Q10. Define: neoplasia, tumor, benign, malignant, metastasis, and cancer.

Background

Topic: Viral Oncology

This question asks for definitions of terms related to abnormal cell growth and cancer, which can be linked to viral infections.

Key Terms:

• Neoplasia

• Tumor

• Benign

• Malignant

• Metastasis

• Cancer

Step-by-Step Guidance

1. Define each term clearly and concisely.

2. Note the differences between benign and malignant growths.

3. Explain how metastasis relates to cancer progression.

Try defining each term before checking the answer!

Final Answer:

Neoplasia: uncontrolled cell growth; Tumor: mass of neoplastic cells; Benign: non-invasive tumor; Malignant: invasive, cancerous tumor; Metastasis: spread of cancer cells; Cancer: disease caused by malignant neoplasia.

Q11. What is the oncogene theory of induction of cancer?

Background

Topic: Viral Carcinogenesis

This question focuses on how viruses can contribute to cancer development by affecting cellular genes.

Key Terms:

• Oncogene

• Proto-oncogene

• Transformation

• Viral integration

Step-by-Step Guidance

1. Define oncogenes and proto-oncogenes.

2. Explain how viruses can activate oncogenes or disrupt normal gene regulation.

3. Describe the process of transformation and its link to cancer.

Try explaining the theory before checking the answer!

Final Answer:

The oncogene theory states that viruses can induce cancer by activating proto-oncogenes or inserting oncogenes, leading to uncontrolled cell growth.

Q12. What are the three main ways viruses are cultured?

Background

Topic: Virus Cultivation

This question asks you to recall laboratory methods for growing and studying viruses.

Key Terms:

• Cell culture

• Embryonated eggs

• Laboratory animals

Step-by-Step Guidance

1. List the three main methods used to culture viruses.

2. Briefly describe each method and its advantages or limitations.

3. Consider which viruses are best suited for each method.

Try listing and describing the methods before checking the answer!

Final Answer:

The three main methods are: cell (tissue) culture, embryonated eggs, and laboratory animals.

Q13. What are viroids?

Background

Topic: Subviral Agents

This question asks you to define viroids and understand their unique features.

Key Terms:

• Viroid

• RNA

• Plant pathogens

Step-by-Step Guidance

1. Define what a viroid is and how it differs from a virus.

2. Describe the structure and genetic material of viroids.

3. Explain what organisms viroids infect.

Try defining viroids before checking the answer!

Final Answer:

Viroids are small, circular RNA molecules that infect plants and lack a protein coat.

Q14. What are prions and how do they replicate?

Background

Topic: Infectious Proteins

This question asks you to define prions and describe their unique replication process.

Key Terms:

• Prion

• Protein misfolding

• Transmissible spongiform encephalopathies

Step-by-Step Guidance

1. Define prions and how they differ from viruses and viroids.

2. Describe the process of prion replication via protein misfolding.

3. Explain the diseases associated with prions.

Try explaining prion replication before checking the answer!

Final Answer:

Prions are infectious proteins that replicate by inducing misfolding of normal proteins, leading to neurodegenerative diseases.