Virology Practice Questions

Q: What is the primary function of the nucleocapsid proteins in the measles virus?

Protect the RNA from degradation during replication.. **Protect the RNA from degradation during replication.** - The **nucleocapsid proteins** (N proteins) in the measles virus encapsidate the **viral RNA genome**, forming a helical ribonucleoprotein (RNP) complex. - This **encapsidation** provides crucial protection to the RNA from cellular **nucleases**, preventing its degradation and maintaining its integrity for successful replication and transcription. *Facilitate the assembly of the virion structure.* - While nucleocapsid proteins are part of the virion structure, their primary function isn't to **facilitate the assembly** but rather to protect the genetic material within that structure. - **Matrix proteins** and other viral components are more directly involved in the overall assembly and budding process. *Assist in the packaging of the viral genome.* - **Packaging** of the viral genome is a separate, although related, process where the protected nucleocapsid is incorporated into the newly forming virion. - The fundamental role of the nucleocapsid protein is the **protection and organization of the RNA**, which then enables efficient packaging. *Protect the genome RNA from nuclease digestion and recognize the location in the cell membrane for budding.* - **Protecting the genome RNA from nuclease digestion** is indeed a key function of nucleocapsid proteins. - However, **recognizing the location in the cell membrane for budding** is primarily mediated by the viral **matrix (M) protein**, which links the nucleocapsid to the envelope glycoproteins.

Q: Which receptors do avian influenza HA viruses primarily bind to?

Alpha 2-3 sialic acid receptors. ***Alpha 2-3 sialic acid receptors*** - Avian influenza viruses preferentially bind to **alpha 2-3 sialic acid receptors**, which are abundant in the **gastrointestinal tract of birds**. - This specificity explains why these viruses primarily infect birds and generally require adaptation to infect humans efficiently. - The α2-3 linkage configuration allows optimal binding of avian HA proteins. *Alpha 2-6 sialic acid receptors* - These receptors are the **primary binding targets for human-adapted influenza A viruses**, found abundantly in the **human upper respiratory tract**. - Avian influenza viruses typically bind less efficiently to α2-6 receptors unless specific mutations occur in the HA protein. - The shift from α2-3 to α2-6 binding preference is a key adaptation for human transmission. *Alpha 2-8 sialic acid receptors* - Alpha 2-8 linkages exist in **polysialic acid chains** and certain gangliosides but are **not recognized binding targets for influenza HA proteins**. - Influenza viruses specifically recognize α2-3 or α2-6 linkages, not α2-8. *Alpha 2-9 sialic acid receptors* - Alpha 2-9 linkages are **not biologically relevant receptors for influenza viruses**. - The key receptor specificity determinant for influenza is the distinction between α2-3 (avian) and α2-6 (human) linkages.

Q: Slapped cheek appearance is caused by:

Parvovirus. ***Parvovirus*** - **Parvovirus B19** causes Fifth disease, characterized by a distinctive bright red rash on the cheeks, which gives the appearance of "slapped cheeks." - This **erythematous rash** is a hallmark symptom, often followed by a lacy or reticular rash on the trunk and limbs. *Measles* - Measles, caused by the **measles virus**, presents with a **maculopapular rash** that starts on the face and spreads downwards, often preceded by **Koplik spots** in the mouth. - It does not typically cause a "slapped cheek" appearance. *Rubella* - Rubella, or **German measles**, is caused by the **rubella virus** and features a milder rash than measles, typically a fine, pink maculopapular rash that starts on the face and spreads to the rest of the body. - It is not associated with the "slapped cheek" rash. *HHV-6* - Human Herpesvirus 6 (HHV-6) is the cause of **roseola infantum**, or Sixth disease, which is characterized by a high fever followed by a sudden **rose-pink rash** on the trunk and neck as the fever breaks. - This rash does not produce the "slapped cheek" appearance.

Q: The paramyxovirus that lacks both hemagglutinin and neuraminidase activities is:

Respiratory syncytial virus. ***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**.

Q: The virus HIV is produced and propagated in:

Circulating T4 lymphocytes. ***Circulating T4 lymphocytes*** - HIV primarily targets and replicates within **CD4+ T lymphocytes** (also known as T4 lymphocytes), which are crucial for the immune response. - The virus uses its **gp120 protein** to bind to the **CD4 receptor** and a coreceptor (CCR5 or CXCR4) on these cells, initiating entry and subsequent replication. *Dendritic cells in the lymph nodes* - Dendritic cells can be infected by HIV, but they primarily function as **reservoirs** and vehicles for transporting the virus to lymph nodes, rather than the main site of productive replication. - While they can transfer HIV to CD4+ T cells, the *primary propagation* occurs in the activated T cells themselves. *B-lymphocytes in the lymph nodes* - **B-lymphocytes** lack the primary **CD4 receptor** and co-receptors (CCR5/CXCR4) necessary for efficient HIV entry and replication. - Therefore, B-cells are generally **not productively infected** by HIV and do not serve as a site for significant viral propagation. *Epithelial cells of the reproductive system* - While HIV can be found in bodily fluids of the reproductive system, **epithelial cells** are generally not the target cells for HIV infection and replication. - The virus primarily targets immune cells, particularly **CD4+ T cells and macrophages**, not epithelial cells of mucosal surfaces for propagation.

Question 1

What is the primary function of the nucleocapsid proteins in the measles virus?

Accepted Answer

Protect the RNA from degradation during replication.

Answer

Facilitate the assembly of the virion structure.

Answer

Assist in the packaging of the viral genome.

Answer

Protect the genome RNA from nuclease digestion and recognize the location in the cell membrane for budding.

Question 2

Which receptors do avian influenza HA viruses primarily bind to?

Accepted Answer

Alpha 2-3 sialic acid receptors

Answer

Alpha 2-9 sialic acid receptors

Answer

Alpha 2-6 sialic acid receptors

Answer

Alpha 2-8 sialic acid receptors

Question 3

Slapped cheek appearance is caused by:

Accepted Answer

Parvovirus

Answer

Measles

Answer

Rubella

Answer

HHV-6

Question 4

The paramyxovirus that lacks both hemagglutinin and neuraminidase activities is:

Accepted Answer

Respiratory syncytial virus

Answer

Mumps virus

Answer

Measles virus

Answer

Parainfluenza virus

Question 5

The virus HIV is produced and propagated in:

Accepted Answer

Circulating T4 lymphocytes

Answer

Dendritic cells in the lymph nodes

Answer

B-lymphocytes in the lymph nodes

Answer

Epithelial cells of the reproductive system

Virology — MCQs

Virology — MCQs

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