Virology Practice Questions

Q: Which one of the following is a function of the enzyme reverse transcriptase, which is unique to retroviruses?

RNA-dependent DNA polymerase activity. ***RNA-dependent DNA polymerase activity*** - **Reverse transcriptase** is a unique enzyme found in retroviruses that synthesizes **DNA from an RNA template**, hence its name "reverse" transcriptase. - This activity is crucial for the retroviral life cycle, as it allows the viral **RNA genome** to be reverse-transcribed into **DNA**, which can then integrate into the host cell's genome. *DNase activity* - **DNase** (deoxyribonuclease) enzymes degrade DNA. This activity is not a primary function of reverse transcriptase. - While integration of the viral DNA into the host genome involves DNA manipulation, the core reverse transcriptase enzyme does not exhibit DNase activity for its primary function. *RNA-dependent RNA polymerase activity* - This activity involves synthesizing **RNA from an RNA template**. It is characteristic of some **RNA viruses** (e.g., influenza virus), but not retroviruses. - Retroviruses use the host cell's machinery to transcribe their integrated DNA provirus into mRNA and new viral RNA genomes, rather than having their own RNA-dependent RNA polymerase. *RNA isomerase activity* - **RNA isomerase activity** is not a standard enzymatic function in the context of nucleic acid synthesis or modification performed by viral enzymes. - Isomerases typically rearrange atoms within a molecule. Reverse transcriptase's primary functions are polymerization and degradation of RNA/DNA hybrids, not isomerization.

Q: Which of the following is a lentivirus?

HIV. ***Correct Answer: HIV*** - **HIV** (Human Immunodeficiency Virus) is the most well-known example of a **lentivirus**, a genus within the **Retroviridae** family. - Lentiviruses are characterized by a long incubation period before disease onset and the ability to cause chronic, slowly progressive diseases. - Key features of lentiviruses include: ability to infect non-dividing cells, integration into host genome, and causing persistent infections. *Incorrect: HBV* - **HBV** (Hepatitis B Virus) belongs to the **Hepadnaviridae** family, not the lentivirus family. - It is a **DNA virus** (not a retrovirus) that primarily infects the liver and can cause acute or chronic hepatitis. *Incorrect: HCV* - **HCV** (Hepatitis C Virus) is a member of the **Flaviviridae** family and is an **RNA virus**. - It is known for causing hepatitis and can lead to chronic infection, cirrhosis, and hepatocellular carcinoma. - Unlike lentiviruses, HCV does not use reverse transcriptase or integrate into the host genome. *Incorrect: Rabies virus* - The **rabies virus** is a member of the **Rhabdoviridae** family, specifically the genus *Lyssavirus*. - It is an **RNA virus** that causes acute encephalitis in mammals, including humans. - Unlike lentiviruses which cause chronic slow infections, rabies causes acute rapidly progressive disease.

Q: Lysis of a bacterial colony in a culture is caused by which agent?

Bacteriophage. ***Bacteriophage*** - **Bacteriophages** are viruses that infect and **lyse bacteria**, creating clear zones (plaques) on a bacterial lawn. - The lysis of bacterial colonies by bacteriophages is a fundamental observation in **microbiology** used to detect and quantify these viruses. *Pox* - **Poxviruses** infect animal cells, not bacteria, and cause diseases like smallpox or cowpox. - Their replication cycle involves host cell machinery but does not result in the *lysis* of bacterial colonies. *HSV* - **Herpes Simplex Virus (HSV)** is a human virus that causes oral and genital lesions. - HSV infects human cells and does not target or lyse bacterial colonies in culture. *CMV* - **Cytomegalovirus (CMV)** is another human virus, part of the herpesvirus family, causing a wide range of clinical manifestations. - CMV infection is specific to human cells and does not cause lysis of bacterial colonies.

Q: The following are true about Epstein-Barr virus (EBV) except which of the following?

The main target of virus is the T-cell lymphocytes. ***The main target of virus is the T-cell lymphocytes*** - This statement is incorrect because **Epstein-Barr virus (EBV)** primarily targets **B-lymphocytes**, not T-cell lymphocytes. - EBV infects B cells by binding to the **CD21 receptor** on their surface. *A member of herpes virus family* - **EBV** is indeed a member of the **Herpesviridae family**, specifically **gammaherpesvirus**. - Other common herpesviruses include **herpes simplex virus (HSV)** and **cytomegalovirus (CMV)**. *Infects epithelial cells of pharynx* - EBV initially infects and replicates in **epithelial cells of the oropharynx**, contributing to viral shedding in saliva. - This initial infection allows the virus to spread to the targeted B-lymphocytes. *It is implicated in nasopharyngeal carcinoma* - EBV is strongly associated with **nasopharyngeal carcinoma (NPC)**, particularly in endemic regions. - It is also linked to other malignancies like **Burkitt lymphoma** and **Hodgkin lymphoma**.

Q: Which of the following statements about arboviruses is correct?

Chikungunya is transmitted by Aedes aegypti.. ***Chikungunya is transmitted by Aedes aegypti.*** - **Chikungunya virus** is primarily transmitted to humans through the bites of infected female **Aedes aegypti** and **Aedes albopictus** mosquitoes. - These mosquitoes are widespread in tropical and subtropical regions and are competent vectors for several arboviruses. *Dengue has only one serotype.* - Dengue virus has **four distinct serotypes** (DEN-1, DEN-2, DEN-3, and DEN-4), meaning infection with one serotype provides immunity to that serotype but not to the others. - Subsequent infection with a different serotype can lead to more severe disease, such as **Dengue Hemorrhagic Fever (DHF)** or **Dengue Shock Syndrome (DSS)**, due to antibody-dependent enhancement. *Kyasanur Forest Disease (KFD) was first identified in Kerala.* - **Kyasanur Forest Disease (KFD)** was first identified in the **Kyasanur Forest** of **Karnataka, India**, not Kerala, in 1957. - It is a **tick-borne hemorrhagic fever** caused by a flavivirus and is endemic to specific regions of India. *Yellow fever is endemic only in Asia.* - **Yellow fever** is endemic in **tropical and subtropical areas of South America and Africa**, not Asia. - The virus is transmitted to humans by infected **mosquitoes, primarily Aedes aegypti**.

Q: Among the following viruses, which one does NOT cause hemagglutination?

HPV. ***HPV*** - **Human Papillomavirus (HPV)** does not possess **hemagglutinin proteins** on its surface. - Hemagglutination is the process where viruses bind to **red blood cells**, causing them to clump together; HPV does not exhibit this property. *Influenza* - **Influenza viruses** have **hemagglutinin (HA) spikes** on their envelope, which bind to sialic acid residues on red blood cells. - This binding leads to **hemagglutination**, a key property used in diagnostic tests like the hemagglutination inhibition assay. *Rubella* - The **Rubella virus** is known to cause **hemagglutination** of red blood cells, particularly from one-day-old chicks or geese. - This property is utilized in the **hemagglutination inhibition (HI) test** for detecting antibodies against the Rubella virus. *Measles* - **Measles virus**, a paramyxovirus, contains **hemagglutinin proteins** on its surface. - These proteins enable the virus to agglutinate red blood cells, a characteristic contributing to its diagnostic detection.

Q: Which virus is primarily associated with Kaposi's sarcoma?

Human herpesvirus 8 (HHV-8). ***Human herpesvirus 8 (HHV-8)*** - **HHV-8**, also known as **Kaposi's sarcoma-associated herpesvirus (KSHV)**, is the causal agent for all forms of Kaposi's sarcoma. - It infects endothelial cells, leading to abnormal proliferation and the characteristic vascular lesions of **Kaposi's sarcoma**, particularly in immunocompromised individuals. *Hepatitis C virus (HCV)* - **HCV** is primarily associated with **hepatocellular carcinoma** and certain **lymphomas**, but not Kaposi's sarcoma. - It causes chronic liver inflammation and can lead to **cirrhosis** and liver failure. *Human papillomavirus (HPV)* - **HPV** is primarily known for causing **cervical cancer**, anogenital warts, and certain **oropharyngeal cancers**. - It does not have a direct causal link to Kaposi's sarcoma. *Herpes simplex virus (HSV)* - **HSV** types 1 and 2 cause **cold sores** (oral herpes) and **genital herpes**, respectively. - While it is a herpesvirus, it is not associated with Kaposi's sarcoma; HHV-8 is a distinct type of herpesvirus.

Q: Which of the following is the envelope glycoprotein of HIV that binds to CD4 receptors for cell entry?

GP120. ***GP120*** - **GP120** is the crucial **envelope glycoprotein** found on the surface of the **Human Immunodeficiency Virus (HIV)**. - It is essential for **viral entry** into host cells by binding to the **CD4 receptor** and a **co-receptor (CCR5 or CXCR4)** on T-helper cells. - This makes it a primary target for **neutralizing antibodies** and **vaccine development**. *Gp73* - **Gp73** is a **Golgi protein** that has been studied as a biomarker for **liver fibrosis** and **hepatocellular carcinoma**. - It is **not associated with HIV** structure or function. *P24* - **P24** is a **capsid protein** of HIV that forms the conical core surrounding the viral RNA. - While it is an important **HIV structural protein** used in diagnostic testing, it is **not an envelope glycoprotein**. - P24 is located **inside the virion**, not on the surface, and does not participate in CD4 receptor binding. *Gp5* - **Gp5** refers to a **glycoprotein** associated with other viruses, such as certain **herpesviruses** like **cytomegalovirus (CMV)**. - It is **not a protein of HIV**.

Q: What is the primary cellular target of Human immunodeficiency virus (HIV)?

CD4+ T cells. ***CD4+ T cells*** - HIV primarily targets and replicates within **CD4+ T lymphocytes**, which are crucial for the body's immune response. - The progressive destruction of these cells leads to **immunodeficiency**, making the body susceptible to opportunistic infections. *Erythrocytes* - **Red blood cells** (erythrocytes) are not directly targeted or infected by HIV. - HIV infection can indirectly lead to **anemia**, but this is not due to direct viral replication within erythrocytes. *Connective tissue cells* - While HIV can have effects on various organs, it does not primarily infect or replicate within **connective tissue cells**. - Its main cellular target is specific immune cells. *Allergy-mediating cells* - **Mast cells** and **basophils** are allergy-mediating cells that are not the primary targets of HIV. - HIV does not directly infect these cells to establish its life cycle.

Q: H1N1 is a subtype of which virus?

Influenza type A virus. ***Influenza type A virus*** - H1N1 refers to the specific **hemagglutinin (H)** and **neuraminidase (N)** proteins on the surface of the virus, which are characteristic of **influenza A viruses**. - Influenza A viruses are known for their ability to undergo **antigenic shift** and cause pandemics, as seen with the 2009 H1N1 pandemic. *SARS virus* - **SARS (Severe Acute Respiratory Syndrome)** is caused by a coronavirus, specifically **SARS-CoV**, which is distinct from influenza viruses. - While both can cause respiratory illness, their genetic structure and mechanisms of infection are entirely different. *Influenza type B virus* - Influenza B viruses primarily infect humans and do not have the same H and N protein classification (e.g., H1N1) that influenza A viruses do. - They tend to cause **seasonal epidemics** but are not typically associated with pandemics. *Influenza type C virus* - Influenza C viruses cause a **mild respiratory illness** and are not classified by H and N subtypes. - They are less common and cause milder symptoms compared to influenza A and B viruses.

Question 1

Which one of the following is a function of the enzyme reverse transcriptase, which is unique to retroviruses?

Accepted Answer

RNA-dependent DNA polymerase activity

Answer

DNase activity

Answer

RNA-dependent RNA polymerase activity

Answer

RNA isomerase activity

Question 2

Which of the following is a lentivirus?

Accepted Answer

HIV

Answer

HBV

Answer

HCV

Answer

Rabies virus

Question 3

Lysis of a bacterial colony in a culture is caused by which agent?

Accepted Answer

Bacteriophage

Answer

Pox

Answer

HSV

Answer

CMV

Question 4

The following are true about Epstein-Barr virus (EBV) except which of the following?

Accepted Answer

The main target of virus is the T-cell lymphocytes

Answer

Infects epithelial cells of pharynx

Answer

It is implicated in nasopharyngeal carcinoma

Answer

A member of herpes virus family

Question 5

Which of the following statements about arboviruses is correct?

Accepted Answer

Chikungunya is transmitted by Aedes aegypti.

Answer

Kyasanur Forest Disease (KFD) was first identified in Kerala.

Answer

Dengue has only one serotype.

Answer

Yellow fever is endemic only in Asia.

Question 6

Among the following viruses, which one does NOT cause hemagglutination?

Accepted Answer

HPV

Answer

Rubella

Answer

Measles

Answer

Influenza

Question 7

Which virus is primarily associated with Kaposi's sarcoma?

Accepted Answer

Human herpesvirus 8 (HHV-8)

Answer

Hepatitis C virus (HCV)

Answer

Human papillomavirus (HPV)

Answer

Herpes simplex virus (HSV)

Question 8

Which of the following is the envelope glycoprotein of HIV that binds to CD4 receptors for cell entry?

Accepted Answer

GP120

Answer

Gp73

Answer

P24

Answer

Gp5

Question 9

What is the primary cellular target of Human immunodeficiency virus (HIV)?

Accepted Answer

CD4+ T cells

Answer

Erythrocytes

Answer

Connective tissue cells

Answer

Allergy-mediating cells

Question 10

H1N1 is a subtype of which virus?

Accepted Answer

Influenza type A virus

Answer

SARS virus

Answer

Influenza type B virus

Answer

Influenza type C virus

Virology — MCQs

Virology — MCQs

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