ICAR AIEEA PG Animal Biotechnology 09 July 2023 (Shift 1) Paper

Viral capsid assembly models in structural virology:

• Hepatitis B virus (HBV) core protein (HBcAg) readily self-assembles in vitro and in recombinant expression systems into highly regular, homogeneous icosahedral capsids ($T=4$ with 120 dimers and $T=3$ with 90 dimers). Due to its robust self-assembly kinetics, defined dimeric building blocks, and ease of biochemical manipulation, HBV core has emerged as the premier model system for studying thermodynamic and structural mechanisms of viral capsid assembly.
• Poxviruses are enormous, complex brick-shaped enveloped viruses with multicomponent coats unsuitable for simple capsid self-assembly studies.
• Rabies virus is an enveloped bullet-shaped rhabdovirus with a helical ribonucleoprotein core.
• Picornaviruses have complex capsid maturation involving proteolytic cleavage of a polyprotein precursor ($P1 \to VP0, VP3, VP1$).

Bacteriophage developmental life cycles:

• The lysogenic cycle involves integration of phage DNA into the bacterial genome where it replicates passively without killing the host cell.
• The lytic cycle (virulent infection) involves active phage genome replication, transcription, structural protein synthesis, virion packaging, and eventual synthesis of endolysins and holins that cause enzymatic lysis and physical bursting (destruction) of the host cell wall to release progeny virions.
• prophage is the latent, quiescent viral genome integrated into the host chromosome during lysogeny.
• Temperate phase refers to phages capable of adopting the dormant lysogenic pathway without destroying the host.

Structural classification of viral particles:

• Primitive virus is an evolutionary term, not a structural classification.
• Virion denotes any complete, infectious extracellular viral particle (which may be either enveloped or non-enveloped).
• Viruses that consist solely of a nucleic acid genome (DNA or RNA) enclosed by a protein shell (capsid) without an outer surrounding lipid bilayer membrane (envelope) are specifically termed naked viruses (non-enveloped viruses, such as picornaviruses, adenoviruses, and reoviruses).
• Capsovirion is a non-standard artificial term.