Viral Replication — MCQs
What is a potential outcome of the integration of a viral genome into a host cell chromosome?
Which is the correct sequence of steps in isolating desirable protein using recombinant DNA technology? 1. Expression of protein and lysis of the bacterial cell 2. Incorporation of genes into bacteria 3. SDS PAGE 4. Protein elution 5. Column chromatography
The paramyxovirus that lacks both hemagglutinin and neuraminidase activities is:
Which of the following is a defective virus?
Cell-matrix adhesions are mediated by?
Which of the following does not have a viral etiology?
What mechanism does Chlamydia use to evade killing by the immune system?
All of the following are RNA viruses except
Influenza virus culture is done on ?
In lymphoid tissue biopsy from a patient with suspected measles, multinucleated giant cells with 'clockwise' nuclear arrangement are observed. What are these cells called?
Viral Replication Indian Medical PG Practice Questions and MCQs
Question 1: What is a potential outcome of the integration of a viral genome into a host cell chromosome?
- A. Altered growth
- B. Malignancy
- C. Latency
- D. All of the options (Correct Answer)
Explanation: ***All of the options*** - The insertion of a viral genome, known as a **provirus**, into the host chromosome can lead to a variety of sustained and complex interactions. - This integration can cause **long-term changes** in cell behavior, including altered gene expression and cell cycle regulation, which may manifest as any of the specified outcomes. *Malignancy* - Viral integration can interrupt or activate host genes, such as **oncogenes** or **tumor suppressor genes**, leading to uncontrolled cell proliferation and potential tumor formation. - An example is **human papillomavirus (HPV)** integrating into host cells, increasing the risk of cervical cancer. *Altered growth* - Integration can change the cell's normal growth patterns, either by promoting excessive division or by causing cell cycle arrest, impacting tissue development and function. - This can be due to the insertion of viral promoters or enhancers near growth-regulating genes. *Latency* - The integrated viral genome can remain dormant within the host chromosome without producing new viral particles for extended periods, a state known as **latency**. - During latency, the virus can be reactivated later to cause a productive infection, as seen with **herpesviruses**.
Question 2: Which is the correct sequence of steps in isolating desirable protein using recombinant DNA technology? 1. Expression of protein and lysis of the bacterial cell 2. Incorporation of genes into bacteria 3. SDS PAGE 4. Protein elution 5. Column chromatography
- A. 2,1,3,5,4 (Correct Answer)
- B. 2,4,5,3,1
- C. 1,2,4,3,5
- D. 1,5,2,4,3
Explanation: ***2,1,3,5,4*** - This sequence accurately reflects the typical order of operations in **recombinant protein isolation**: first, the gene is introduced into bacteria, then protein is expressed and cells lysed, followed by **SDS-PAGE as an intermediate quality check** to confirm protein expression before proceeding to purification steps (column chromatography and elution). - The process starts with gene incorporation, includes an analytical checkpoint after lysis, and ends with purified protein elution. *2,4,5,3,1* - This sequence is incorrect because **protein elution (4)** and **column chromatography (5)** are purification steps that occur *after* protein expression and cell lysis. - **Lysis (1)** cannot happen after elution, as cells must be lysed first to release the protein for purification. *1,2,4,3,5* - This sequence is incorrect because **expression and lysis (1)** must occur *after* the gene has been **incorporated into bacteria (2)** - the gene must be present before it can be expressed. - Additionally, **protein elution (4)** should follow **column chromatography (5)**, as elution is the step where protein is collected from the chromatography column. *1,5,2,4,3* - This sequence is incorrect because **incorporation of genes (2)** must be the first step - the gene needs to be in the bacteria before any expression, lysis, or purification can occur. - Starting with **expression and lysis (1)** before gene incorporation is impossible.
Question 3: The paramyxovirus that lacks both hemagglutinin and neuraminidase activities is:
- A. Mumps virus
- B. Respiratory syncytial virus (Correct Answer)
- C. Measles virus
- D. Parainfluenza virus
Explanation: ***Respiratory syncytial virus*** - **Respiratory syncytial virus (RSV)** is unique among paramyxoviruses because it **lacks both hemagglutinin (HA) and neuraminidase (NA)** surface glycoproteins. - Instead, RSV uses its **fusion (F) protein** to mediate viral entry and induce syncytia formation. *Mumps virus* - Mumps virus possesses both **hemagglutinin and neuraminidase (HN) activity** on a single surface glycoprotein. - This HN protein is crucial for **viral attachment and release** from host cells. *Measles virus* - Measles virus has **hemagglutinin (H)** activity for attachment but **lacks neuraminidase activity**. - Its F protein is essential for **cell fusion** and spread. *Parainfluenza virus* - Parainfluenza viruses, like mumps, possess a **hemagglutinin-neuraminidase (HN) protein** with both activities. - This dual function is important for their **lifecycle and pathogenesis**.
Question 4: Which of the following is a defective virus?
- A. HAV
- B. HBV
- C. HCV
- D. HDV (Correct Answer)
Explanation: ***HDV*** - **Hepatitis D virus (HDV)** is a unique **defective RNA virus** that requires the **Hepatitis B surface antigen (HBsAg)** for its replication and assembly. - It uses **HBsAg** as its envelope protein, meaning it can only infect and cause disease in individuals who are also infected with **HBV**. *HAV* - **Hepatitis A virus (HAV)** is a **non-enveloped RNA picornavirus** with a single-stranded RNA genome. - It is a **complete, independent virus** capable of replicating without the assistance of other viruses. *HBV* - **Hepatitis B virus (HBV)** is a **partially double-stranded DNA hepadnavirus** that can replicate independently. - While it coinfects with HDV, it does not require another virus for its own replication or infectivity. *HCV* - **Hepatitis C virus (HCV)** is a **single-stranded RNA flavivirus** that is fully capable of independent replication. - It is an enveloped virus but does not rely on co-infection with other hepatitis viruses for its life cycle.
Question 5: Cell-matrix adhesions are mediated by?
- A. Integrins (Correct Answer)
- B. Selectins
- C. Calmodulin
- D. Cadherins
Explanation: ***Integrins*** - **Integrins** are transmembrane receptors that mediate cell adhesion to the **extracellular matrix (ECM)**, linking it to the cell's cytoskeleton. - They bind to various ECM components like **fibronectin**, **collagen**, and **laminin**. *Cadherins* - **Cadherins** are primarily involved in **cell-to-cell adhesion**, forming junctions like **adherens junctions** and **desmosomes**. - They are **calcium-dependent adhesion molecules** that do not directly bind to the extracellular matrix. *Selectins* - **Selectins** are cell adhesion molecules involved in **leukocyte rolling** and **adhesion to endothelial cells** during inflammation. - They mediate **transient cell-to-cell interactions**, not cell-matrix adhesion. *Calmodulin* - **Calmodulin** is a **calcium-binding protein** that acts as a signal transducer, regulating various intracellular processes. - It is involved in **calcium-dependent signaling pathways** and enzyme activation, not cell adhesion.
Question 6: Which of the following does not have a viral etiology?
- A. Hepatocellular carcinoma
- B. Nasopharyngeal carcinoma
- C. Colorectal adenocarcinoma
- D. Breast ductal carcinoma (Correct Answer)
Explanation: ***Hodgkin's lymphoma*** - Hodgkin's lymphoma is primarily associated with **genetic factors** and environmental triggers instead of a viral cause [1][2]. - It can arise from **Reed-Sternberg cells**, which are not related to viral infections [1][2]. - EBV is not associated with certain subtypes of Hodgkin lymphoma [3]. *Nasopharyngeal carcinoma* - Strongly linked to **Epstein-Barr virus (EBV)**, which plays a significant role in its pathogenesis. - It is characterized by **nasal obstruction** and symptoms related to tumor invasion, with a clear viral etiology. *Hepatocellular carcinoma* - Often associated with **hepatitis B and C viruses**, which are well-known risk factors for liver cancer. - Chronic infection leads to **cirrhosis**, predisposing individuals to carcinoma development. *Burkitt's lymphoma* - Associated with **EBV**, particularly in endemic forms in Africa, affecting the jaw or abdomen [4]. - It involves **aggressive B-cell proliferation**, strongly linked to viral infection [4]. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Diseases Of The Urinary And Male Genital Tracts, pp. 556-557. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, pp. 614-616. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, p. 618. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 335-336.
Question 7: What mechanism does Chlamydia use to evade killing by the immune system?
- A. Inhibiting phagolysosome fusion (Correct Answer)
- B. Causing cell membrane perforation
- C. Molecular mimicry in immune evasion
- D. Producing immune-modulating factors
Explanation: ***Inhibiting phagolysosome fusion*** - *Chlamydia* **prevents the fusion of the phagosome** (containing the bacterium) with the lysosome, thus avoiding the degradative enzymes and low pH environment that would kill it. - This mechanism allows *Chlamydia* to **replicate intracellularly** within a protected vacuole called an **inclusion body**. - This is the **most direct mechanism** by which *Chlamydia* evades intracellular killing. *Molecular mimicry in immune evasion* - **Molecular mimicry** involves pathogens displaying antigens similar to host tissues, leading to **autoimmune damage** rather than evasion of killing. - While this may contribute to chronic complications of *Chlamydia* infection, it is not the primary mechanism *Chlamydia* employs to directly **evade intracellular destruction** by immune cells. *Causing cell membrane perforation* - **Cell membrane perforation** would typically lead to cell lysis and release of intracellular contents, which is counterproductive for an **obligate intracellular pathogen** like *Chlamydia*. - Instead, *Chlamydia* **maintains host cell integrity** to establish its replicative niche within the inclusion body. *Producing immune-modulating factors* - While *Chlamydia* does produce **immune-modulating factors** to suppress host immune responses, this is a **secondary mechanism** that complements its survival strategy. - The question specifically asks about evading **killing**, which is most directly achieved by **preventing phagolysosome fusion** and the resulting exposure to lysosomal enzymes. - Immune modulation affects the broader immune response but does not directly prevent the bacterium from being killed once inside a phagosome.
Question 8: All of the following are RNA viruses except
- A. Influenza virus
- B. Parainfluenza virus
- C. Mumps virus
- D. Herpes virus (Correct Answer)
Explanation: ***Herpes virus*** - **Herpesviruses** are a large family of **DNA viruses** that cause diseases in animals, including humans. - They are characterized by their ability to establish **latent infections** and periodically reactivate. *Influenza virus* - The **influenza virus** is an **RNA virus** belonging to the family **Orthomyxoviridae**. - It is known for causing the seasonal **flu** and respiratory infections. *Parainfluenza virus* - **Parainfluenza viruses** are a group of **RNA viruses** in the family **Paramyxoviridae**. - They are a common cause of **respiratory tract infections**, especially in children, leading to conditions like **croup**. *Mumps virus* - The **mumps virus** is an **RNA virus** that is part of the **Paramyxoviridae** family. - It is well-known for causing **mumps**, which is characterized by the swelling of the **parotid glands**.
Question 9: Influenza virus culture is done on ?
- A. Chorioallantoic membrane
- B. Allantoic cavity (Correct Answer)
- C. Yolk sac
- D. All of the options
Explanation: ***Allantoic cavity*** - The **allantoic cavity** of embryonated chicken eggs is the standard and most effective site for isolating and propagating **influenza viruses** for vaccine production and research. - This cavity provides an optimal environment for viral replication, particularly yielding high titers of **hemagglutinin**, a key influenza antigen. *Chorioallantoic membrane* - While embryonated eggs are used for virus culture, the **chorioallantoic membrane (CAM)** is primarily used for cultivating viruses that produce **pocks** (visible lesions), such as Vaccinia and Herpes Simplex Virus. - Influenza virus growth on the CAM is less efficient and typically doesn't produce distinct pocks, making it unsuitable for high-yield propagation compared to the allantoic cavity. *Yolk sac* - The **yolk sac** of embryonated eggs is ideal for growing viruses or bacteria that require a **lipid-rich environment** and replicate intracellularly, such as Chlamydia or Rickettsia. - It is not the preferred site for influenza virus isolation or proliferation due to suboptimal conditions for viral replication and lower viral yields. *All of the options* - While all these sites are components of an embryonated chicken egg, each serves as a host for different types of microorganisms or for specific purposes in virology. - For **influenza virus culture**, the **allantoic cavity** is the specifically utilized site for optimal growth and high viral yield.
Question 10: In lymphoid tissue biopsy from a patient with suspected measles, multinucleated giant cells with 'clockwise' nuclear arrangement are observed. What are these cells called?
- A. Cowdry type A
- B. Warthin-Finkeldey cells (Correct Answer)
- C. Negri bodies
- D. Henderson-Paterson bodies
Explanation: ***Warthin-Finkeldey cells*** - These are **multinucleated giant cells** with many nuclei arranged in a **\"clockwise\" or syncytial pattern**, a characteristic histopathological finding in **lymphoid tissues (lymph nodes, tonsils, spleen) during prodromal measles**. - They represent a key diagnostic marker for measles infection, formed by the fusion of infected lymphoid cells. - They are typically found **before the appearance of the measles rash**. *Cowdry type A* - **Cowdry type A inclusion bodies** are intranuclear inclusions characteristic of **herpes simplex virus** and **varicella-zoster virus** infections. - They are eosinophilic inclusions surrounded by a clear halo, seen in herpesvirus-infected cells, not measles. *Negri bodies* - **Negri bodies** are eosinophilic, cytoplasmic inclusion bodies found in neurons (especially hippocampal pyramidal cells), characteristic of **rabies infection**. - They are pathognomonic for rabies virus and are not observed in measles. *Henderson-Paterson bodies* - **Henderson-Paterson bodies** are large, eosinophilic intracytoplasmic inclusions (molluscum bodies) found in epidermal cells infected with **molluscum contagiosum virus**. - They are pathognomonic for molluscum contagiosum and have no association with measles.
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