Virus Core Structure: Genome and Capsid (Nucleocapsid)

The core of a virus particle (virion) is the nucleocapsid, composed of:

• Viral genome: Either DNA or RNA (single- or double-stranded, linear or circular).
• Capsid: Protein shell made of repeating subunits (capsomeres) that encloses and protects the genome.

Additional Structures (Virus-Dependent)

• Envelope: Lipid bilayer derived from host cell membrane, studded with viral glycoproteins (e.g., influenza, HIV, herpesviruses).
• Matrix proteins: Link capsid to envelope (e.g., M1 in influenza).
• Tegument proteins: In herpesviruses, a layer between capsid and envelope containing regulatory proteins.

Function

The nucleocapsid delivers the genome into the host cell. Capsid stability, genome packaging, and receptor-binding proteins on the surface determine infectivity and host range.