Each capsid is composed of protein subunits called capsomeres . The capsid can be composed of a single protein or several proteins depending upon the virus. The envelope is a membrane c omposed of glycolipids, proteins and carbohydrates. The envelope originates from host plasma membrane when the virus buds out of the cell. Viruses without an envelope are known as naked.
Viruses come in all shapes and sizes but none can be seen by a light microscope.
The capsid or envelope determines the shape of the virion . Cultivation of Viruses Viruses are difficult to grow, primarily because they need a host to grow in. Also, when they infect this host they generally kill it. The availability of tissue culture has greatly simplified the growth of animal viruses. These are eucaryotic cells that are grown in an incubator and can be infected under very controlled conditions.