what are capsids
capsid. the shell of protein that protects the nucleic acid of a virus; it is composed of structural units, or capsomers. According to the number of subunits possessed by capsomers, they are called dimers (2), trimers (3), pentamers (5), or hexamers (6).(kap'sid),apsid. the shell of protein that protects the nucleic acid of a virus; it is composed of structural units, or capsomers. According to the number of subunits possessed by capsomers, they are called dimers (2), trimers (3), pentamers (5), or hexamers (6). (kap'sid),