What makes up a viral capsid?
The viral capsid consists of several oligomeric structural subunits called capsomeres.
Capsomeres are made up of protein subunits called protomeres. Capsid proteins are coded for by the viral genome. Because of its limited size, the genome codes for only a few structural proteins. Capsids are formed as single or double protein shells and consist of only one or a few structural protein species.
Capsomeres self assemble to form the capsid. Various arrangements of capsomeres are - icosahedral, helical and complex.
One of the major functions of the capsid is to introduce the enclosed viral genome into host cells by adsorbing readily to host cell surface. Thus the capsid is important in determining the host range and antigenic composition of the virion.