Microbiology Study Guide: Viruses, Replication Cycles, and Related Concepts

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Q1. Describe the bacteriophage lytic and lysogenic replication.

Background

Topic: Bacteriophage Replication Cycles

This question tests your understanding of the two main replication strategies used by bacteriophages (viruses that infect bacteria): the lytic and lysogenic cycles.

Key Terms:

Lytic cycle: A viral replication process resulting in the destruction (lysis) of the host cell and release of new phage particles.
Lysogenic cycle: A viral replication process where the phage genome integrates into the host genome and replicates along with it without immediately destroying the host.
Prophage: The integrated phage DNA in the bacterial chromosome during lysogeny.

Step-by-Step Guidance

Start by outlining the steps of the lytic cycle: attachment, penetration, biosynthesis, maturation, and release.
Next, describe the lysogenic cycle: attachment, penetration, integration of phage DNA into the host genome (forming a prophage), and replication with the host cell.
Explain how the lysogenic cycle can switch to the lytic cycle under certain conditions (induction).
Compare the outcomes for the host cell in each cycle (immediate lysis vs. survival with integrated viral DNA).

Try solving on your own before revealing the answer!

Final Answer:

Lytic replication: The bacteriophage attaches to the bacterial cell, injects its DNA, takes over the host's machinery to produce new phage components, assembles new phages, and lyses (breaks open) the host cell to release progeny phages.

Lysogenic replication: The phage DNA integrates into the host's chromosome, becoming a prophage. The host cell survives and divides, copying the prophage DNA along with its own. The prophage can later be induced to enter the lytic cycle.

Q2. Understand the steps in the lysogenic cycle and how the lysogenic cycle presents an evolutionary advantage to the temperate bacteriophage.

Background

Topic: Lysogenic Cycle and Evolutionary Advantages

This question focuses on the detailed steps of the lysogenic cycle and why it benefits temperate phages (those capable of lysogeny).

Key Terms:

Temperate phage: A bacteriophage capable of both lytic and lysogenic cycles.
Prophage: Phage DNA integrated into the host genome.
Lysogeny: The state in which the phage genome is maintained in the host without causing lysis.

Step-by-Step Guidance

List the steps of the lysogenic cycle: attachment, penetration, integration, replication, and possible induction.
Describe what happens to the phage DNA during integration and how it is replicated with the host genome.
Discuss how the lysogenic cycle allows the phage to persist in the host population without killing the host immediately.
Consider why this persistence can be advantageous for the phage in terms of survival and spread.

Try solving on your own before revealing the answer!

Final Answer:

The lysogenic cycle involves the integration of phage DNA into the host genome, forming a prophage. The host cell survives and divides, passing the prophage to daughter cells. This allows the phage to persist in the population without killing the host, providing an evolutionary advantage by ensuring the phage's genetic material is maintained during times when host cells are scarce or conditions are unfavorable for lytic replication.

Q3. How does the lysogenic cycle differ from the lytic cycle?

Background

Topic: Comparison of Viral Replication Cycles

This question asks you to compare and contrast the two main bacteriophage replication strategies.

Key Terms:

Lytic cycle
Lysogenic cycle
Prophage

Step-by-Step Guidance

Identify the main steps and outcomes of the lytic cycle (immediate replication and host cell lysis).
Identify the main steps and outcomes of the lysogenic cycle (integration and dormancy).
Compare the fate of the host cell in each cycle.
Discuss the potential for switching from lysogenic to lytic under certain conditions.

Try solving on your own before revealing the answer!

Final Answer:

The lytic cycle results in the immediate production of new phages and lysis of the host cell, while the lysogenic cycle involves integration of the phage genome into the host DNA, allowing the host to survive and replicate with the prophage. The lysogenic cycle can later switch to the lytic cycle under certain conditions.

Q4. Understand the steps of animal virus replication.

Background

Topic: Animal Virus Replication

This question tests your knowledge of the general steps involved in the replication of animal viruses, which can differ from bacteriophage replication.

Key Terms:

Attachment
Penetration
Uncoating
Biosynthesis
Maturation
Release

Step-by-Step Guidance

List the main steps: attachment, penetration, uncoating, biosynthesis, maturation, and release.
Describe what happens during each step (e.g., how the virus enters the cell, how its genome is replicated, etc.).
Note differences between enveloped and non-enveloped viruses in the release step.
Consider how the host cell machinery is used during biosynthesis.

Try solving on your own before revealing the answer!

Final Answer:

The steps of animal virus replication are: (1) attachment to the host cell, (2) penetration (entry), (3) uncoating of the viral genome, (4) biosynthesis of viral components, (5) maturation (assembly of new virions), and (6) release of new viruses from the host cell (by budding for enveloped viruses or lysis for non-enveloped viruses).

Q5. Understand the following key differences between enveloped and non-enveloped viruses:

Background

Topic: Viral Structure and Release Mechanisms

This question focuses on the structural differences between enveloped and non-enveloped viruses and how these differences affect their entry and exit from host cells.

Key Terms:

Enveloped virus: Virus with a lipid membrane derived from the host cell.
Non-enveloped virus: Virus lacking a lipid envelope; only a protein capsid surrounds the genome.
Budding: Process by which enveloped viruses acquire their envelope and exit the host cell.
Lysis: Destruction of the host cell, releasing non-enveloped viruses.

Step-by-Step Guidance

Explain how enveloped viruses enter host cells (fusion with the cell membrane).
Describe how enveloped viruses acquire their envelope during the budding process.
Discuss how non-enveloped viruses exit the host cell (lysis) and do not acquire an envelope.
Summarize the implications of these differences for viral transmission and immune evasion.

Try solving on your own before revealing the answer!

Final Answer:

a. Enveloped viruses can enter host cells by fusion with the cell membrane. b. Enveloped viruses acquire their envelope as they bud from the host cell. c. Non-enveloped viruses do not bud from the host cell; instead, they are released by lysis, destroying the host cell.

Q6. Understand how the process of retrovirus biosynthesis works (hint: involves reverse transcriptase!).

Background

Topic: Retrovirus Replication

This question tests your understanding of how retroviruses replicate, focusing on the role of reverse transcriptase.

Key Terms and Enzymes:

Retrovirus: An RNA virus that uses reverse transcriptase to synthesize DNA from its RNA genome.
Reverse transcriptase: An enzyme that converts viral RNA into complementary DNA (cDNA).
Provirus: The integrated viral DNA in the host genome.

Step-by-Step Guidance

Describe how the retrovirus enters the host cell and releases its RNA genome.
Explain the function of reverse transcriptase in converting viral RNA into DNA.
Discuss how the newly synthesized DNA integrates into the host genome, forming a provirus.
Outline how the host cell machinery is then used to produce new viral RNA and proteins.

Try solving on your own before revealing the answer!

Final Answer:

Retrovirus biosynthesis involves the entry of the virus into the host cell, release of its RNA genome, and use of reverse transcriptase to synthesize complementary DNA (cDNA) from the RNA template. This DNA integrates into the host genome as a provirus, which is then transcribed and translated by the host cell to produce new viral particles.

Q7. What is a provirus? What family of viruses can form proviruses?

Background

Topic: Viral Integration

This question asks you to define a provirus and identify which viruses are capable of forming one.

Key Terms:

Provirus: Viral DNA that is integrated into the host cell's genome and can be replicated along with it.
Retroviridae: The family of viruses (including HIV) that form proviruses.

Step-by-Step Guidance

Define what a provirus is and how it differs from other viral forms.
Identify the virus family most associated with provirus formation.
Explain the significance of provirus formation in viral persistence and latency.

Try solving on your own before revealing the answer!

Final Answer:

A provirus is viral DNA that has been integrated into the host cell's genome. Retroviruses (family Retroviridae), such as HIV, are known to form proviruses as part of their replication cycle.

Q8. Understand that a prophage is not the same as a provirus!

Background

Topic: Viral Integration Terminology

This question tests your ability to distinguish between a prophage (bacteriophage DNA in bacteria) and a provirus (animal virus DNA in eukaryotic cells).

Key Terms:

Prophage: Integrated phage DNA in a bacterial genome.
Provirus: Integrated viral DNA in a eukaryotic host genome.

Step-by-Step Guidance

Define both terms: prophage and provirus.
Identify the type of host cell associated with each (bacterial vs. eukaryotic).
Explain why the distinction is important in microbiology.

Try solving on your own before revealing the answer!

Final Answer:

A prophage is phage DNA integrated into a bacterial genome, while a provirus is viral DNA integrated into a eukaryotic host genome. The terms refer to similar processes but in different types of host cells.

Q9. Several kinds of cancer are known to be caused by viruses.

Background

Topic: Oncogenic Viruses

This question highlights the role of certain viruses in causing cancer (oncogenesis).

Key Terms:

Oncogenic virus: A virus capable of causing cancer.
Transformation: The process by which a normal cell becomes cancerous.

Step-by-Step Guidance

List examples of viruses known to cause cancer (e.g., HPV, EBV, Hepatitis B and C).
Describe how viral infection can lead to transformation of host cells.
Explain the mechanisms by which viral genes can disrupt normal cell regulation.

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Final Answer:

Examples of viruses that can cause cancer include Human Papillomavirus (HPV), Epstein-Barr Virus (EBV), Hepatitis B and C viruses, and Human T-cell Leukemia Virus (HTLV-1). These viruses can disrupt normal cell cycle regulation, leading to uncontrolled cell growth and cancer.

Q10. What is a latent viral infection? Can you give an example?

Background

Topic: Viral Latency

This question asks you to define latent viral infections and provide an example.

Key Terms:

Latent infection: A viral infection in which the virus remains dormant within the host cell and can reactivate later.
Reactivation: The process by which a latent virus becomes active again.

Step-by-Step Guidance

Define what is meant by a latent viral infection.
Describe how the virus persists in the host without causing symptoms.
Think of a common example of a virus that establishes latency in humans.

Try solving on your own before revealing the answer!

Final Answer:

A latent viral infection is one in which the virus remains dormant within the host cell and can reactivate later. An example is Herpes Simplex Virus (HSV), which can remain latent in nerve cells and reactivate to cause cold sores.

Q11. What is a persistent viral infection? Can you give an example?

Background

Topic: Persistent Viral Infections

This question asks you to define persistent viral infections and provide an example.

Key Terms:

Persistent infection: A viral infection in which the virus is continuously present in the host, often at low levels, over a long period.
Chronic infection: A type of persistent infection with ongoing viral replication.

Step-by-Step Guidance

Define what is meant by a persistent viral infection.
Describe how the virus remains in the host and continues to replicate.
Think of an example of a virus that causes persistent infection in humans.

Try solving on your own before revealing the answer!

Final Answer:

A persistent viral infection is one in which the virus remains in the host and continues to replicate over a long period, often causing ongoing or recurring symptoms. An example is Hepatitis B virus, which can cause chronic liver infection.

Q12. What are prions?

Background

Topic: Infectious Proteins

This question asks you to define prions and understand their role in disease.

Key Terms:

Prion: An infectious protein that can cause neurodegenerative diseases.
Protein misfolding: The process by which prions induce normal proteins to adopt an abnormal conformation.

Step-by-Step Guidance

Define what a prion is and how it differs from viruses and bacteria.
Describe how prions cause disease through protein misfolding.
Note that prions lack nucleic acids (DNA or RNA).

Try solving on your own before revealing the answer!

Final Answer:

Prions are infectious proteins that cause disease by inducing abnormal folding of specific normal cellular proteins, primarily in the brain. They do not contain nucleic acids and are responsible for several neurodegenerative diseases.

Q13. Can you give examples of prion diseases?

Background

Topic: Prion Diseases

This question asks you to list diseases caused by prions.

Key Terms:

Transmissible spongiform encephalopathies (TSEs): A group of progressive, fatal brain diseases caused by prions.

Step-by-Step Guidance

Recall the main human and animal diseases caused by prions.
List at least two examples for each (human and animal).

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Final Answer:

Examples of prion diseases include Creutzfeldt-Jakob disease (CJD) and kuru in humans, and bovine spongiform encephalopathy (BSE, or "mad cow disease") and scrapie in animals.

Q14. What is antigenic shift?

Background

Topic: Viral Evolution

This question asks you to define antigenic shift, a process important in the evolution of certain viruses like influenza.

Key Terms:

Antigenic shift: A major change in viral antigens due to genetic reassortment, often leading to new viral strains.
Reassortment: The mixing of genetic material from different viral strains infecting the same cell.

Step-by-Step Guidance

Define antigenic shift and explain how it occurs.
Identify which viruses are most known for antigenic shift (e.g., influenza A).
Discuss the consequences of antigenic shift for public health (e.g., pandemics).

Try solving on your own before revealing the answer!

Final Answer:

Antigenic shift is a major change in the surface antigens of a virus, typically due to genetic reassortment between different viral strains. This process is common in influenza A viruses and can lead to the emergence of new strains capable of causing pandemics.

Q15. What is antigenic drift?

Background

Topic: Viral Evolution

This question asks you to define antigenic drift, a process that leads to gradual changes in viral antigens.

Key Terms:

Antigenic drift: Small, gradual changes in viral antigens due to point mutations during replication.
Mutation: A change in the nucleotide sequence of the viral genome.

Step-by-Step Guidance

Define antigenic drift and explain how it occurs.
Identify which viruses are most affected by antigenic drift (e.g., influenza viruses).
Discuss the implications for vaccine effectiveness and epidemics.

Try solving on your own before revealing the answer!

Final Answer:

Antigenic drift is the gradual accumulation of mutations in viral genes that code for surface antigens, leading to minor changes in the virus over time. This process is common in influenza viruses and can result in seasonal epidemics.

Q16. Define pandemic and understand that it can be brought about by antigenic shift in a virus.

Background

Topic: Epidemiology

This question asks you to define a pandemic and relate it to antigenic shift.

Key Terms:

Pandemic: An epidemic that has spread over multiple countries or continents, usually affecting a large number of people.
Antigenic shift: Major changes in viral antigens that can lead to pandemics.

Step-by-Step Guidance

Define what a pandemic is in epidemiological terms.
Explain how antigenic shift can lead to the emergence of new viral strains capable of causing pandemics.
Provide an example of a pandemic caused by antigenic shift (e.g., 2009 H1N1 influenza).

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Final Answer:

A pandemic is an epidemic that spreads across multiple countries or continents, affecting a large number of people. Antigenic shift in viruses like influenza can create new strains to which the population has little immunity, leading to pandemics.

Q17. Define epidemic and understand that it can be brought about by antigenic drift in a virus.

Background

Topic: Epidemiology

This question asks you to define an epidemic and relate it to antigenic drift.

Key Terms:

Epidemic: A sudden increase in the number of cases of a disease above what is normally expected in a specific area.
Antigenic drift: Minor changes in viral antigens that can lead to epidemics.

Step-by-Step Guidance

Define what an epidemic is in epidemiological terms.
Explain how antigenic drift can cause new viral variants that lead to epidemics.
Provide an example of an epidemic caused by antigenic drift (e.g., seasonal influenza outbreaks).

Try solving on your own before revealing the answer!

Final Answer:

An epidemic is a sudden increase in the number of cases of a disease above what is normally expected in a specific area. Antigenic drift in viruses like influenza can lead to new variants that cause epidemics.

Q18. Know the following virus families and associated diseases:

Background

Topic: Virus Families and Diseases

This question tests your ability to match virus families with the diseases they cause.

Key Terms:

Papovaviridae: Associated with human warts and some cancers.
Herpesviridae: Causes herpes and chicken pox (Varicellavirus).
Filoviridae: Enveloped helical viruses (e.g., Ebola).
Retroviridae: Lentivirus (HIV); all use reverse transcriptase and form a provirus.
Picornaviridae: Rhinovirus causes the common cold.
Orthomyxoviridae: Influenzavirus causes the flu.

Step-by-Step Guidance

Review each virus family and the diseases associated with them.
Note any unique features (e.g., reverse transcriptase in Retroviridae).
Match each family to its corresponding disease(s).

Try solving on your own before revealing the answer!

Final Answer:

a. Papovaviridae: human warts and some cancers b. Herpesviridae: herpes and chicken pox (Varicellavirus) c. Filoviridae: enveloped helical viruses (e.g., Ebola) d. Retroviridae: Lentivirus (HIV); all use reverse transcriptase and form a provirus e. Picornaviridae: Rhinovirus causes the common cold f. Orthomyxoviridae: Influenzavirus causes the flu

Q19. Be able to describe the properties of specificity versus sensitivity for diagnostic tests.

Background

Topic: Diagnostic Test Performance

This question asks you to explain the difference between specificity and sensitivity in the context of diagnostic tests.

Key Terms and Formulas:

Sensitivity: The ability of a test to correctly identify those with the disease (true positive rate).
Specificity: The ability of a test to correctly identify those without the disease (true negative rate).

Step-by-Step Guidance

Define sensitivity and specificity in your own words.
Write the formulas for each:
Explain why both properties are important in evaluating diagnostic tests.

Try solving on your own before revealing the answer!

Final Answer:

Sensitivity measures a test's ability to correctly identify individuals with the disease (true positives), while specificity measures its ability to correctly identify those without the disease (true negatives). High sensitivity reduces false negatives; high specificity reduces false positives.

Q20. Be able to describe potential antiviral drug targets.

Background

Topic: Antiviral Therapy

This question asks you to identify and describe possible targets for antiviral drugs in the viral life cycle.

Key Terms:

Antiviral drug target: A specific step or molecule in the viral life cycle that can be inhibited to prevent viral replication.
Examples: Entry inhibitors, reverse transcriptase inhibitors, protease inhibitors, integrase inhibitors, neuraminidase inhibitors.

Step-by-Step Guidance

List the main stages of the viral life cycle (entry, replication, assembly, release).
Identify which stages or viral enzymes can be targeted by drugs.
Give examples of drug classes that act at each stage (e.g., reverse transcriptase inhibitors for HIV).

Try solving on your own before revealing the answer!

Final Answer:

Potential antiviral drug targets include viral entry (entry inhibitors), genome replication (reverse transcriptase or polymerase inhibitors), protein processing (protease inhibitors), integration into the host genome (integrase inhibitors), and viral release (neuraminidase inhibitors). Targeting these steps can prevent the virus from completing its life cycle.