The protective protein coat of a virus, known as a viral capsid, covers the nucleic acid inside the virus and protects it while the virus inserts itself into the host. The capsid proteins help the virus attach to and penetrate into host cells in order to infect the host.
The viral capsid is a shell that is composed of different structural proteins. This structure covers and protects the nucleic acid within the virus, which is either ribonucleic acid or deoxyribonucleic acid, but not both RNA and DNA. Without a capsid, the nucleic acid can become degraded by digestive enzymes of host cells.