Consequently, they are obligate intracellular parasites . Viral replication depends on the expression of the viral genome for the formation of the viral proteins. This is accomplished by hijacking host components such as ribosomes, enzymes etc.
Viral genomes are extremely small.
In some cases, they only encode three or four proteins. 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.