Virology VIVA Questions and Answers with Mnemonics
The field of Virology, the study of viruses, is a core component of Microbiology and requires a deep understanding of classification, structure, replication, and pathogenesis. For students preparing for practical or oral examinations (VIVA), mastering key concepts and high-yield facts is crucial. This comprehensive guide is structured in a question-and-answer format, utilizing powerful mnemonics to aid in rapid memory recall, transforming complex virological data into easily digestible information for exam success. The questions cover fundamental concepts and the classification of major viral families based on their nucleic acid and structural properties.
Fundamental Viral Concepts
Q: Define a virus. Why are they called obligatory intracellular parasites?
A: A virus is the smallest obligatory intracellular parasite with only one type of nucleic acid (either RNA or DNA) in its genome. They are called obligatory intracellular parasites because they lack the necessary cellular machinery—specifically, ribosomes and mitochondria—to generate energy (ATP) or synthesize proteins independently. Consequently, they must replicate within a host cell, effectively hijacking the host’s enzymes and energy-yielding apparatus for their own propagation. Outside a living cell, they are inert particles.
Q: What is a defective virus? Give an example.
A: A defective virus is one that lacks one or more functional genes required for its replication. Therefore, it requires the ‘help’ of another, unrelated virus (a helper virus) to successfully complete its life cycle. The classic example is the Hepatitis D virus (HDV), which is defective and requires the presence of the Hepatitis B virus (HBV) to provide the necessary surface antigen (HBsAg) for its packaging and entry into new cells.
Q: Name the major phases of the virus replication cycle.
A: The phases of the virus replication cycle, which can be broken down for examination, include: 1) Attachment & Penetration, 2) Uncoating of the viral genome, 3) Early viral mRNA synthesis (Transcription), 4) Early viral protein synthesis (Translation), 5) Viral genome replication, 6) Late viral mRNA synthesis, 7) Late viral protein synthesis, 8) Assembly/Progeny virion assembly, and 9) Virion release from the cell.
DNA Viruses: Classification and Key Properties
DNA viruses are generally double-stranded (dsDNA), linear, have an icosahedral capsid, and replicate in the host cell nucleus. Success in VIVA requires knowing the exceptions to these general rules, often aided by specific mnemonics.
Q: List the major families of DNA viruses using a common mnemonic.
A: Use the mnemonic “HHAPPPPy CHEVrolet” to recall the major DNA virus families: – **H**epadnavirus
– **H**erpesvirus (which itself includes sub-families like CMV, HSV-1, HSV-2, HHV-6, EBV, VZV)
– **A**denovirus
– **P**arvovirus
– **P**apillomavirus
– **P**olyomavirus
– **P**oxvirus
Q: What are the three major exceptions to the ‘DNA virus rules’ regarding nucleic acid and replication site?
A: The three critical exceptions are:1. **ssDNA:** **Parvovirus** is the only single-stranded DNA virus. (Mnemonic: *Parvo is ‘part’ of a double strand*).
2. **Circular DNA:** **Hepadnavirus, Papillomavirus, and Polyomavirus** have circular DNA. (Mnemonic: *HiPPies have circular signs*).
3. **Cytoplasmic Replication:** **Poxvirus** is the only DNA virus that replicates entirely in the cytoplasm. (Mnemonic: *Poxvirus has a complex structure and is too large to enter the nucleus*).
RNA Viruses: Classification and Key Properties
RNA viruses are extremely diverse. Their classification is based on their strandedness (+/- sense), shape (icosahedral/helical), and envelope status, with many important mnemonics to aid recall.
Q: Which RNA viruses have a naked capsid (non-enveloped)? What is the mnemonic?
A: All RNA viruses are enveloped, except for the three families with naked capsids: **Picornavirus, Calicivirus, and Reovirus** (which is also the only dsRNA virus). The mnemonic is **PCR** (Picornavirus, Calicivirus, Reovirus). This simple three-letter mnemonic is a high-yield VIVA fact.
Q: What is the main exception to the rule that all RNA viruses replicate in the cytoplasm?
A: All RNA viruses replicate in the cytoplasm, with the exceptions of **Influenza virus** (part of the Orthomyxovirus family) and **Retrovirus**. They replicate in the host cell nucleus.
Q: List the positive-sense (+) single-stranded RNA viruses and the mnemonic for them.
A: These viruses have genomes that can act directly as mRNA for protein synthesis. A mnemonic to list them is: **Call Pico and Flavi To Come Rightaway** – Families: **C**alicivirus, **Pico**rnavirus, **Flavi**virus, **To**gavirus, **Corona**virus, **Retro**virus.
Q: What does it mean for an RNA virus to be negative-sense (-)? List the families and a mnemonic.
A: A negative-sense RNA virus has a genome complementary to the mRNA. Because the host cell cannot transcribe the (-) strand directly, these viruses must carry their own enzyme, **RNA-dependent RNA Polymerase (RdRp)**, to first transcribe their (-) genome into a (+) sense mRNA inside the host cell. The mnemonic is: **Always Bring Polymerase Or Fail Replication**
– Families: **A**renavirus, **B**unyavirus, **P**aramyxovirus, **O**rthomyxovirus, **F**ilovirus, **R**habdovirus.
Viral Transmission and Pathogenesis
A crucial VIVA skill is the ability to recall specific transmission routes and causative agents for common diseases, often integrating virology with bacteriology and parasitology.
Q: Name the viruses and other organisms that are transmitted vertically (from mother to fetus/child). What is the mnemonic provided for the viral component?
A: Vertical transmission occurs in several organisms, collectively often remembered by the TORCH complex. The mnemonic **ESR-pH-cH** is provided as a guide for key pathogens in this context: – **E**pstein Barr Virus (EBV)
– **S**yphilis (T. pallidum, a bacterium) or **H**erpes **S**implex Virus (HSV)
– **R**ubella virus
– **P**arvovirus
– **H**IV
– **C**ytomegalovirus (CMV)
– **H**epatitis B & C virus
It is important to remember that this category mixes viruses and other pathogens, demanding an integrated approach in the examination setting.
Q: Distinguish between the causative agents for Chickenpox and Bacillary Dysentery.
A: Chickenpox is caused by the **Varicella-Zoster Virus (VZV)**, a DNA virus from the Herpesvirus family. Bacillary Dysentery is caused by the bacterium **Shigella dysenteriae**. This highlights the necessity of distinguishing between viral and bacterial pathogens for correct diagnosis and treatment.
Q: What virus causes the Common Cold, and which virus causes Chickenpox?
A: The Common Cold is most frequently caused by the **Rhinovirus**, a positive-sense, single-stranded RNA virus from the Picornavirus family. Chickenpox is caused by the **Varicella-Zoster Virus (VZV)**.
Conclusion: The Strategy of Mnemonics in Virology
Success in a Virology VIVA is not solely about exhaustive knowledge but also about quick, confident recall of specific details, which is where mnemonics prove invaluable. By associating viral families, their unique properties (like the Parvovirus being ssDNA or the Poxvirus replicating in the cytoplasm), and the diseases they cause with memorable phrases or images, students can efficiently retrieve information under extreme exam pressure. The interconnected nature of these facts—from the viral genome type to the required host machinery and the ultimate outcome of infection—necessitates a systematic approach to study. Utilizing these structured questions and proven mnemonics allows for a rapid mental checklist of high-yield virology facts, enabling students to move beyond simple memorization to functional, applicable knowledge.