• Basic terminology
o Virion a complete virus particle. An infectious particle.
o Capsid a protein coat which encloses the genome of the virus.
o Nucleocapsid this is a protein coat which comes into direct contact with the genome.
o Envelope lipid bilayer which also acts to carry viral glycoproteins.
• There are three main types of structures that viral capsids may take upon:
• Capsid/nucleocapsids play multiple roles, however their primary function is to protect the genome from environmental harm.
o Protection from dessication (enveloped viruses are more prone to dessication)
o Protection from gastric acids
o Many capsids will also determine the host range due to the receptors that are present on the surface.
This may also be used to determine the serology of a virus particle.
o Nucleocapsids often function to make sure the genome is “delivered” to the proper destination.
• The envelope is very similar to the cells lipid bilayer.
o It contains glycoproteins which are largely used for recognition of cell receptor and the ability to gain entry into a cell.
• Viral receptors are those proteins which are part of the envelope or the capsid and will determine the host range of the virus.
• Often times the virion will have a nonstructural component already packaged with it.
o This is largely because the item it needs from the cell is either not readily available or unable to be utilized.
These consist of viral enzymes: polymerases, reverse transcriptase.
Others: transcription factors, host defense attack.
• Those proteins which actively contribute to the structure of a complete virion are considered to be structural proteins.
• Those proteins which are not an active part of a complete virion particle and carry out a different function not related to structure are known as non-structural (ie polymerases, TF).
• Taxonomic classification of virus particles are based upon: