Protein
Proteins are the most versatile macromolecules in living systems and they play important roles in essentially all biological processes. Protein makes up the capsid of a virus. The infective extracellular form of a virus known as a virion contains at least one unique protein synthesized by specific genes in the nucleic acid of that virus. In almost all viruses, at least one of these proteins forms a shell (called a capsid) around the nucleic acid. Certain viruses also have other proteins internal to the capsid. Some of these proteins act as enzymes during the synthesis of viral nucleic acids.