A<unk>  is the protein shell of a virus. It consists of several oligomeric subunits made of protein. The<unk>  encloses the genetic material of the virus.<unk> s are broadly classified according to their structure.  The majority of viruses have<unk> s with either helical or icosahedral structure.  Some viruses, such as bacteriophages, have developed more complicated structures.  The icosahedral shape, which has 20 equilateral triangular faces, approximates a sphere, while the helical shape is cylindrical.  The<unk>  faces may consist of one or more proteins.  For example, the foot-and-mouth disease virus<unk>  has faces consisting of three proteins named VP1-3.
Some viruses are enveloped, meaning that the<unk>  is coated with a lipid membrane known as the viral envelope.  The envelope is acquired by the<unk>  from an intracellular membrane; some examples would include the inner nuclear membrane, the golgi membrane, or the cell's outer membrane.
Once the virus has infected the cell, it will start replicating itself, using the mechanisms of the infected host cell. During this process, new<unk>  subunits are synthesized according to the genetic material of the virus, using the protein biosynthesis mechanism of the cell.  During the assembly process, a portal subunit is assembled at one vertex of the<unk> .  Through this portal, viral DNA or RNA is transported into the<unk> .  The structure and assembly of the Herpes virus<unk>  Portal Protein has been imaged via cryo-electron microscopy.
Structural analyses of major<unk>  protein (MCP) architectures have been used to<unk> tegorise viruses into families. For example, the bacteriophage PRD1, Paramecium bursaria Chlorella algal virus, and mammalian adenovirus have been placed in the same family.
Capsid
Electron shell
Viral vector
Macrocycle
Vector
Vector 
Transfer RNA
Diatomic molecule