(SEM VIII) THEORY EXAMINATION 2024-25 VIROLOGY

VIROLOGY (KOE087)

B.Tech – Semester VIII | Theory Examination 2024–25

SECTION A

(Attempt all questions – brief but descriptive)

a) Commonly used antiretroviral drug classes

Antiretroviral drugs are used in the treatment of HIV infection to suppress viral replication and prevent disease progression. Two commonly used classes are reverse transcriptase inhibitors, which block the conversion of viral RNA into DNA, and protease inhibitors, which prevent the maturation of newly formed viral particles by inhibiting viral protease enzymes.

b) Viral diagnostic techniques used in clinical practice

Viral diagnostic techniques are essential for identifying viral infections accurately. Commonly used methods include polymerase chain reaction (PCR), which detects viral nucleic acids with high sensitivity, and enzyme-linked immunosorbent assay (ELISA), which detects viral antigens or host antibodies against viruses.

c) Conventional vaccines and their types

Conventional vaccines are traditional vaccines prepared using whole pathogens or their components to induce immunity. These vaccines stimulate the immune system to recognize and respond to pathogens. Two main types of conventional vaccines are live attenuated vaccines, which use weakened forms of the virus, and inactivated vaccines, which contain killed viruses that cannot replicate.

d) Antiviral libraries

Antiviral libraries refer to large collections of chemical compounds or molecules that are screened for antiviral activity. These libraries are used in drug discovery to identify potential inhibitors that can block viral replication, entry, or assembly. High-throughput screening of antiviral libraries accelerates the development of new antiviral drugs.

e) Viruses from Herpesviridae and Poxviridae families

An example of a virus belonging to the Herpesviridae family is Herpes simplex virus, which causes oral and genital herpes. An example from the Poxviridae family is Variola virus, the causative agent of smallpox.

f) Enzyme responsible for converting viral RNA into DNA

In retroviruses, the enzyme responsible for converting viral RNA into DNA is reverse transcriptase. This enzyme synthesizes complementary DNA from the viral RNA template, which is a crucial step in the retroviral life cycle.

g) Common shapes of viral capsids

Viral capsids commonly exhibit icosahedral symmetry, which forms a spherical structure, and helical symmetry, where the capsid proteins are arranged in a spiral around the viral genome. These shapes provide structural stability and protect viral genetic material.

h) Virus family responsible for dengue and its genome type

Dengue virus belongs to the Flaviviridae family. It contains a positive-sense single-stranded RNA genome, which acts directly as mRNA for viral protein synthesis after infection.

i) Difference between cytokines and interferons

Cytokines are small signaling proteins released by immune cells to regulate immune responses, inflammation, and cell communication. Interferons are a specific group of cytokines that play a crucial role in antiviral defense by inhibiting viral replication and activating immune cells.

j) Virion and its difference from living organisms

A virion is a complete, infectious viral particle consisting of nucleic acid enclosed within a protein coat, sometimes surrounded by a lipid envelope. Unlike living organisms, virions lack cellular structures, do not carry out metabolism, and can replicate only inside a host cell.

SECTION B

(Attempt any three – long descriptive answers)

a) Virus classification systems and nomenclature

Virus classification is based on structural, genetic, and replication characteristics. Modern classification systems consider factors such as type of nucleic acid, symmetry of the capsid, presence or absence of an envelope, and replication strategy. The Baltimore classification system categorizes viruses based on genome type and method of mRNA synthesis, while the International Committee on Taxonomy of Viruses provides standardized nomenclature to ensure uniform naming and classification worldwide.

b) Strategies used by retroviruses for integration and persistence

Retroviruses integrate into the host genome using reverse transcription followed by integration of viral DNA into host chromosomes. This integration allows the virus to persist for long periods and evade immune detection. Latency, continuous low-level replication, and genetic variability contribute to disease progression and long-term infection.

c) Pathogenic mechanism of rabies virus

Rabies virus enters the body through animal bites and initially replicates in muscle cells. It then travels through peripheral nerves to the central nervous system using retrograde axonal transport. The virus causes neuronal dysfunction rather than cell destruction, leading to symptoms such as hydrophobia, paralysis, and ultimately death. Host immune responses are limited due to immune evasion by the virus.

d) Structure and replication cycle of Influenza virus

Influenza virus is an enveloped virus with a segmented negative-sense RNA genome. Its envelope contains hemagglutinin and neuraminidase proteins, which play roles in attachment and release. Replication occurs in the host cell nucleus, involving transcription, translation, assembly, and budding. Antigenic variation through drift and shift makes influenza difficult to control.

e) Naked and enveloped viruses

Naked viruses lack a lipid envelope and consist only of a capsid surrounding the genome, making them more resistant to environmental conditions. Examples include adenovirus and poliovirus. Enveloped viruses possess a lipid membrane derived from host cells, making them more sensitive but better at immune evasion. Examples include HIV and influenza virus.

SECTION C

(Attempt any one part from each question)

3(a) DNA vaccine and subunit vaccine with role of adjuvants

DNA vaccines introduce genetic material encoding viral antigens into host cells, leading to in situ antigen production and immune activation. Subunit vaccines contain purified viral proteins and are safer but less immunogenic. Adjuvants enhance immune responses by stimulating antigen-presenting cells and prolonging antigen exposure.

3(b) Molecular biology of SARS-CoV and public health impact

SARS-CoV is a positive-sense RNA virus encoding structural and non-structural proteins essential for replication. Its spike protein mediates host cell entry via ACE2 receptors. The virus caused severe respiratory illness and had a major public health impact due to rapid transmission, high mortality, and global spread.

4(a) Historical milestones in virology

The discovery of viruses began with the identification of filterable agents by Ivanovsky and Beijerinck. Later advances such as electron microscopy, cell culture techniques, and molecular biology revealed viral structure, replication, and genetics, establishing virology as a distinct scientific discipline.

4(b) HIV structure, replication and pathogenesis of AIDS

HIV is an enveloped retrovirus containing RNA, reverse transcriptase, and envelope glycoproteins. It infects CD4+ T cells, integrates into the host genome, and causes progressive immune deficiency. Loss of immune function leads to opportunistic infections characteristic of AIDS.

5(a) Effect of viral infections on host macromolecules

Viruses hijack host cellular machinery to synthesize viral proteins and nucleic acids. They alter host DNA replication, RNA transcription, and protein synthesis. For example, poliovirus shuts down host protein synthesis, while hepatitis viruses disrupt liver cell metabolism.

5(b) Differences among positive-strand RNA viruses and Picornaviruses

Positive-strand RNA viruses use their genome directly as mRNA. Picornaviruses are a subgroup characterized by small size, naked capsids, and cytoplasmic replication. Differences exist in genome organization, pathogenesis, and host range.

6(a) Oncogenesis by DNA viruses

DNA viruses such as Human papillomavirus cause cancer by integrating viral genes that disrupt cell cycle regulation. Viral proteins inactivate tumor suppressor genes, leading to uncontrolled cell division and malignant transformation.

6(b) Viral mechanisms to counter host antiviral defenses

Viruses evade host defenses by inhibiting interferon signaling, mutating antigenic proteins, blocking apoptosis, and hiding within host cells. These strategies allow prolonged infection and immune escape.

7(a) siRNA and ribozymes in viral control

siRNA mediates gene silencing by degrading viral RNA, while ribozymes are catalytic RNA molecules that cleave viral genomes. Both represent modern antiviral strategies targeting viral replication at the molecular level.

7(b) Life cycle of retroviruses

Retroviruses enter host cells, reverse transcribe their RNA into DNA, integrate into the host genome, and use host machinery for transcription and translation. Reverse transcription is a defining feature and key target for antiviral therapy.