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Comprehensive Study Guide for Chapter 13: Viruses (Microbiology)

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Q1. List the various characteristics of viruses.

Background

Topic: Viral Structure and Properties

This question tests your understanding of the fundamental features that define viruses and distinguish them from other microorganisms.

Key Terms:

  • Virus

  • Obligate intracellular parasite

  • Genome (DNA or RNA)

  • Capsid

  • Host specificity

Step-by-Step Guidance

  1. Recall that viruses are not considered living organisms because they cannot carry out metabolism or reproduce independently.

  2. Think about the basic structural components that all viruses possess (e.g., genetic material and a protein coat).

  3. Consider how viruses replicate and what makes them obligate intracellular parasites.

  4. List any additional features that may be present in some, but not all, viruses (such as envelopes or enzymes).

Try solving on your own before revealing the answer!

Final Answer:

  • Viruses are acellular, obligate intracellular parasites.

  • They contain either DNA or RNA as their genetic material, but never both.

  • All viruses have a protein coat called a capsid that surrounds their genetic material.

  • Some viruses have an outer lipid envelope derived from the host cell membrane.

  • Viruses lack ribosomes and metabolic machinery; they rely entirely on the host cell for replication.

  • They are much smaller than bacteria and can only be seen with an electron microscope.

  • Viruses exhibit host specificity, infecting only certain cell types.

These characteristics distinguish viruses from cellular life forms.

Q2. Distinguish between the characteristics of bacteria and viruses.

Background

Topic: Microbial Classification

This question assesses your ability to compare and contrast the fundamental differences between bacteria (prokaryotic cells) and viruses (acellular entities).

Key Terms:

  • Bacteria: Prokaryotic, cellular, living organisms

  • Viruses: Acellular, non-living, obligate intracellular parasites

  • Cell structure, metabolism, replication

Step-by-Step Guidance

  1. List the defining features of bacteria, such as cell structure, genetic material, and metabolic capabilities.

  2. List the defining features of viruses, focusing on their lack of cellular structure and dependence on host cells.

  3. Compare their modes of replication and ability to carry out metabolism.

  4. Think about their visibility under microscopes and their response to antibiotics.

Try solving on your own before revealing the answer!

Final Answer:

  • Bacteria are living, single-celled prokaryotes with cellular structures (cell wall, plasma membrane, ribosomes, etc.), capable of independent metabolism and reproduction by binary fission.

  • Viruses are non-living, acellular particles that lack cellular structures and metabolic machinery; they require a host cell for replication.

  • Bacteria contain both DNA and RNA, while viruses contain either DNA or RNA, never both.

  • Bacteria can be seen with a light microscope; viruses require an electron microscope.

  • Antibiotics can kill bacteria but are ineffective against viruses.

These differences are fundamental to understanding microbial classification and treatment strategies.

Q3. What components are found in all viruses and what are their functions?

Background

Topic: Viral Structure

This question focuses on the universal structural components of viruses and their roles in the viral life cycle.

Key Terms:

  • Genome (DNA or RNA)

  • Capsid

  • Capsomere

Step-by-Step Guidance

  1. Identify the two components that are present in all viruses.

  2. Describe the function of the viral genome.

  3. Describe the function of the capsid and its subunits (capsomeres).

  4. Consider any additional components that may be present in some, but not all, viruses.

Try solving on your own before revealing the answer!

Final Answer:

  • All viruses contain a nucleic acid genome (either DNA or RNA) that carries the genetic information necessary for replication.

  • All viruses have a protein coat called a capsid, made up of capsomeres, which protects the genome and aids in attachment to host cells.

Some viruses may also have an envelope and enzymes, but these are not universal.

Q4. What are spikes?

Background

Topic: Viral Structure – Surface Proteins

This question tests your knowledge of viral surface structures and their roles in infection.

Key Terms:

  • Spikes (peplomers)

  • Attachment

  • Host specificity

Step-by-Step Guidance

  1. Recall what structures are found on the surface of some viruses, especially enveloped viruses.

  2. Think about the function of these structures in the viral life cycle, particularly in host cell recognition and entry.

  3. Consider how spikes contribute to host specificity and immune response.

Try solving on your own before revealing the answer!

Final Answer:

Spikes are glycoprotein projections found on the surface of some viruses, especially enveloped viruses. They facilitate attachment to specific receptors on host cells and determine host specificity. Spikes can also be targets for the host immune response.

Q5. What is an envelope and when do viruses acquire their envelope?

Background

Topic: Viral Structure – Envelopes

This question examines your understanding of the viral envelope, its origin, and its significance in the viral life cycle.

Key Terms:

  • Envelope

  • Lipid bilayer

  • Budding

  • Host cell membrane

Step-by-Step Guidance

  1. Define what a viral envelope is and what it is composed of.

  2. Explain how and when viruses acquire their envelope during the replication cycle.

  3. Consider the role of the envelope in viral infectivity and immune evasion.

Try solving on your own before revealing the answer!

Final Answer:

The envelope is a lipid bilayer derived from the host cell membrane, surrounding the capsid of some viruses. Viruses acquire their envelope during the process of budding from the host cell, typically at the plasma membrane or internal membranes. The envelope contains viral proteins (including spikes) that aid in attachment and entry into new host cells.

Q6. Explain the key differences between the entry and exit stages of enveloped vs. non-enveloped viruses.

Background

Topic: Viral Replication – Entry and Exit Mechanisms

This question tests your understanding of how different types of viruses enter and exit host cells, focusing on the role of the viral envelope.

Key Terms:

  • Enveloped virus

  • Non-enveloped virus

  • Fusion

  • Endocytosis

  • Budding

  • Lysis

Step-by-Step Guidance

  1. Describe how enveloped viruses typically enter host cells (e.g., membrane fusion or endocytosis).

  2. Describe how non-enveloped viruses enter host cells (e.g., endocytosis or direct penetration).

  3. Explain how enveloped viruses exit host cells (e.g., budding, which preserves the host cell).

  4. Explain how non-enveloped viruses exit host cells (e.g., cell lysis, which destroys the host cell).

Try solving on your own before revealing the answer!

Final Answer:

  • Enveloped viruses typically enter host cells by fusing their envelope with the host cell membrane or via endocytosis, and exit by budding, acquiring their envelope from the host membrane.

  • Non-enveloped viruses usually enter by endocytosis or direct penetration and exit by causing cell lysis, which destroys the host cell.

Q7. Compare the stages of animal virus replication with bacteriophage replication.

Background

Topic: Viral Replication Cycles

This question asks you to compare the replication processes of viruses that infect animal cells versus those that infect bacteria (bacteriophages).

Key Terms:

  • Attachment

  • Penetration

  • Biosynthesis

  • Maturation/Assembly

  • Release

  • Lytic cycle

  • Lysogenic cycle

Step-by-Step Guidance

  1. List the general stages of viral replication common to both animal viruses and bacteriophages.

  2. Identify key differences in how animal viruses and bacteriophages attach to and enter their host cells.

  3. Consider differences in the release mechanisms (e.g., budding vs. lysis).

  4. Think about the presence of envelopes in animal viruses and their absence in most bacteriophages.

Try solving on your own before revealing the answer!

Final Answer:

  • Both animal viruses and bacteriophages undergo attachment, penetration, biosynthesis, maturation, and release.

  • Bacteriophages inject their DNA into the bacterial cell, while animal viruses often enter by endocytosis or membrane fusion.

  • Animal viruses may have an envelope and can exit by budding; bacteriophages typically cause host cell lysis for release.

  • Bacteriophages can undergo lysogenic cycles, integrating their DNA into the host genome as a prophage.

Q8. Explain the role of the three key enzymes found in HIV.

Background

Topic: Retroviruses – HIV Enzymes

This question tests your knowledge of the enzymes that are essential for HIV replication and their specific functions.

Key Terms:

  • Reverse transcriptase

  • Integrase

  • Protease

Step-by-Step Guidance

  1. Identify the three enzymes packaged within the HIV virion.

  2. Describe the function of reverse transcriptase in converting viral RNA to DNA.

  3. Explain the role of integrase in incorporating viral DNA into the host genome.

  4. Describe how protease processes viral proteins during maturation.

Try solving on your own before revealing the answer!

Final Answer:

  • Reverse transcriptase synthesizes complementary DNA (cDNA) from the viral RNA genome.

  • Integrase inserts the newly synthesized viral DNA into the host cell's genome.

  • Protease cleaves viral polyproteins into functional proteins, essential for assembling new virions.

Q9. Explain the specific mechanism of action of NRTIs (Example: Acyclovir) and NNRTIs.

Background

Topic: Antiviral Drugs – HIV Therapy

This question focuses on how nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs) inhibit HIV replication.

Key Terms:

  • NRTIs (Nucleoside/Nucleotide Reverse Transcriptase Inhibitors)

  • NNRTIs (Non-Nucleoside Reverse Transcriptase Inhibitors)

  • Reverse transcriptase

  • Chain termination

Step-by-Step Guidance

  1. Describe how NRTIs mimic natural nucleosides and are incorporated into viral DNA.

  2. Explain how this incorporation leads to chain termination during DNA synthesis.

  3. Describe how NNRTIs bind to reverse transcriptase and inhibit its activity by a different mechanism.

  4. Consider the clinical significance of these drugs in HIV therapy.

Try solving on your own before revealing the answer!

Final Answer:

  • NRTIs (e.g., Acyclovir) are analogs of natural nucleosides; they are incorporated into viral DNA by reverse transcriptase, causing chain termination and halting DNA synthesis.

  • NNRTIs bind directly to reverse transcriptase at a site distinct from the active site, causing a conformational change that inhibits enzyme activity.

Q10. Explain the specific mechanism of action of protease inhibitors.

Background

Topic: Antiviral Drugs – HIV Therapy

This question tests your understanding of how protease inhibitors block HIV maturation.

Key Terms:

  • Protease inhibitor

  • Viral polyprotein

  • Virion maturation

Step-by-Step Guidance

  1. Recall the role of HIV protease in processing viral polyproteins into functional proteins.

  2. Describe how protease inhibitors interfere with this process.

  3. Explain the effect of protease inhibition on the production of infectious virions.

Try solving on your own before revealing the answer!

Final Answer:

Protease inhibitors block the activity of HIV protease, preventing the cleavage of viral polyproteins into functional proteins. As a result, immature, non-infectious virions are produced, reducing viral replication.

Q11. Explain the key events that occur during the lytic cycle.

Background

Topic: Bacteriophage Replication – Lytic Cycle

This question tests your understanding of the steps involved in the lytic replication cycle of bacteriophages.

Key Terms:

  • Lytic cycle

  • Attachment

  • Penetration

  • Biosynthesis

  • Maturation

  • Release

Step-by-Step Guidance

  1. List the sequential steps of the lytic cycle.

  2. Describe what happens during attachment and penetration.

  3. Explain the biosynthesis of viral components.

  4. Describe maturation and release, focusing on host cell lysis.

Try solving on your own before revealing the answer!

Final Answer:

  • Attachment: The phage attaches to specific receptors on the bacterial surface.

  • Penetration: The phage injects its DNA into the host cell.

  • Biosynthesis: Host machinery is used to synthesize phage DNA and proteins.

  • Maturation: New phage particles are assembled.

  • Release: The host cell lyses, releasing new phages.

Q12. Explain the key events that occur during the lysogenic cycle.

Background

Topic: Bacteriophage Replication – Lysogenic Cycle

This question focuses on the steps and significance of the lysogenic cycle in bacteriophages.

Key Terms:

  • Lysogenic cycle

  • Prophage

  • Integration

  • Induction

Step-by-Step Guidance

  1. List the steps of the lysogenic cycle.

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

  3. Explain the concept of a prophage and its replication with the host cell.

  4. Consider what triggers the switch from lysogenic to lytic cycle (induction).

Try solving on your own before revealing the answer!

Final Answer:

  • Attachment and penetration occur as in the lytic cycle.

  • Phage DNA integrates into the host genome, becoming a prophage.

  • The prophage is replicated along with the host cell's DNA during cell division.

  • Environmental triggers can induce the prophage to excise and enter the lytic cycle.

Q13. What is prophage?

Background

Topic: Lysogeny

This question tests your understanding of the term "prophage" in the context of bacteriophage replication.

Key Terms:

  • Prophage

  • Lysogenic cycle

  • Integration

Step-by-Step Guidance

  1. Recall what happens to phage DNA during the lysogenic cycle.

  2. Define the term used for integrated phage DNA within the bacterial chromosome.

  3. Consider the significance of the prophage for both the virus and the host cell.

Try solving on your own before revealing the answer!

Final Answer:

A prophage is phage DNA that has been integrated into the bacterial host genome during the lysogenic cycle. It is replicated along with the host DNA and can remain dormant until induced to enter the lytic cycle.

Q14. Explain phage conversion.

Background

Topic: Lysogeny – Phage Conversion

This question examines your understanding of how lysogenic phages can alter the phenotype of their bacterial hosts.

Key Terms:

  • Phage conversion

  • Lysogenic conversion

  • Toxin genes

Step-by-Step Guidance

  1. Define phage conversion and how it occurs during lysogeny.

  2. Consider examples where phage genes confer new properties to the host bacterium.

  3. Think about the implications for bacterial pathogenicity.

Try solving on your own before revealing the answer!

Final Answer:

Phage conversion (lysogenic conversion) is the process by which a bacterium acquires new traits, such as toxin production, due to the expression of genes carried by a prophage. This can increase bacterial virulence.

Q15. What is transduction? Distinguish between specialized and generalized transduction.

Background

Topic: Horizontal Gene Transfer – Transduction

This question tests your understanding of how bacteriophages mediate gene transfer between bacteria and the differences between the two main types of transduction.

Key Terms:

  • Transduction

  • Generalized transduction

  • Specialized transduction

  • Lytic cycle

  • Lysogenic cycle

Step-by-Step Guidance

  1. Define transduction as a mechanism of horizontal gene transfer.

  2. Describe how generalized transduction occurs during the lytic cycle.

  3. Describe how specialized transduction occurs during the lysogenic cycle.

  4. Compare the types of bacterial genes transferred in each process.

Try solving on your own before revealing the answer!

Final Answer:

  • Transduction is the transfer of bacterial genes from one bacterium to another via a bacteriophage.

  • Generalized transduction occurs during the lytic cycle when random bacterial DNA is packaged into phage particles.

  • Specialized transduction occurs during the lysogenic cycle when specific bacterial genes adjacent to the prophage are transferred.

Q16. Influenza

Background

Topic: Influenza Virus – Epidemiology and Prevention

This question covers multiple aspects of influenza virus transmission, prevention, vaccination, and antigenic variation.

Key Terms:

  • Transmission

  • Prevention

  • Vaccination

  • Antigenic drift

  • Antigenic shift

Step-by-Step Guidance

  1. For transmission, recall how influenza spreads from person to person.

  2. For prevention, list common strategies to reduce influenza infection.

  3. Identify populations recommended for vaccination.

  4. Explain how the composition of the flu vaccine is determined each year.

  5. Describe the two mechanisms (antigenic drift and shift) by which influenza viruses change.

Try solving on your own before revealing the answer!

Final Answer:

  • Transmission: Influenza spreads via respiratory droplets from coughing, sneezing, or talking.

  • Prevention: Vaccination, hand hygiene, respiratory etiquette, and avoiding close contact with sick individuals.

  • Who should get vaccinated? Everyone over 6 months old, especially high-risk groups (elderly, young children, pregnant women, immunocompromised).

  • Vaccine composition: Determined annually based on surveillance of circulating strains worldwide.

  • Mechanisms of change: Antigenic drift (small mutations in HA/NA genes) and antigenic shift (major genetic reassortment leading to new subtypes).

Q17. Human Papillomavirus (HPV)

Background

Topic: HPV – Transmission, Health Effects, Prevention, and Treatment

This question covers the epidemiology, health consequences, and management of HPV infection.

Key Terms:

  • HPV

  • Transmission

  • Cervical cancer

  • Vaccination

  • Treatment

Step-by-Step Guidance

  1. Describe how HPV is transmitted.

  2. List health problems caused by HPV infection.

  3. Identify prevention strategies, including vaccination.

  4. Discuss available treatments for HPV-related conditions.

Try solving on your own before revealing the answer!

Final Answer:

  • Transmission: Primarily through sexual contact.

  • Health problems: Genital warts, cervical cancer, and other anogenital cancers.

  • Prevention: HPV vaccination, safe sex practices, regular screening (Pap smears).

  • Treatment: Removal of warts, treatment of precancerous lesions, but no cure for the virus itself.

Q18. Hepatitis B virus

Background

Topic: Hepatitis B – Transmission, Prevention, and Types of Infection

This question covers the epidemiology, prevention, and clinical types of Hepatitis B infection.

Key Terms:

  • Hepatitis B

  • Transmission

  • Prevention

  • Acute vs. chronic infection

Step-by-Step Guidance

  1. Describe the main routes of Hepatitis B transmission.

  2. List prevention strategies, including vaccination.

  3. Explain the difference between acute and chronic Hepatitis B infection.

Try solving on your own before revealing the answer!

Final Answer:

  • Transmission: Blood, sexual contact, perinatal (mother to child).

  • Prevention: Vaccination, safe injection practices, screening blood products.

  • Types of infection: Acute (short-term, self-limited) and chronic (long-term, can lead to liver disease and cancer).

Q19. Epstein-Barr virus (Human herpesvirus 4)

Background

Topic: EBV – Diseases, Transmission, and Epidemiology

This question covers the diseases caused by EBV, their symptoms, transmission, prevention, and epidemiological factors.

Key Terms:

  • Epstein-Barr virus (EBV)

  • Burkitt's lymphoma

  • Mononucleosis

  • Transmission

  • Prevention

Step-by-Step Guidance

  1. Define Burkitt's lymphoma and its association with EBV.

  2. List common symptoms of EBV infection.

  3. Describe how EBV is transmitted.

  4. Discuss prevention strategies.

  5. Consider why Burkitt's lymphoma is more common in Africa.

Try solving on your own before revealing the answer!

Final Answer:

  • Burkitt's lymphoma: A type of cancer of the lymphatic system associated with EBV infection, especially in African children.

  • Symptoms: Fever, sore throat, swollen lymph nodes, fatigue (mononucleosis).

  • Transmission: Saliva ("kissing disease").

  • Prevention: No vaccine; avoid sharing drinks or utensils.

  • Burkitt's lymphoma in Africa: More common due to co-infection with malaria, which weakens immune response.

Q20. Distinguish between latent and persistent viral infections. Provide examples of each type of infection.

Background

Topic: Viral Pathogenesis – Latency vs. Persistence

This question tests your understanding of the differences between latent and persistent viral infections and asks for examples of each.

Key Terms:

  • Latent infection

  • Persistent infection

  • Herpes simplex virus

  • HIV

Step-by-Step Guidance

  1. Define latent viral infection and describe its characteristics.

  2. Define persistent viral infection and describe its characteristics.

  3. Provide examples of viruses that cause each type of infection.

  4. Consider the clinical implications of each type.

Try solving on your own before revealing the answer!

Final Answer:

  • Latent infection: The virus remains dormant within the host cell and can reactivate later (e.g., Herpes simplex virus, Varicella-zoster virus).

  • Persistent infection: The virus is continuously present and replicates at low levels over a long period (e.g., HIV, Hepatitis B, Hepatitis C).

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