The outer protein coat of a virus is known as the

• A. Capsid
• B. Nucleoid
• C. Envelope
• D. Genome

Answer: (A)

The outer protein shell of a virus is called the capsid. This protein coat is built from subunits called capsomeres and serves to protect the viral genome and help deliver it into a host cell by attaching to receptors on the cell surface. Some viruses also have an envelope, a lipid membrane derived from the host that sits outside the capsid and carries viral glycoproteins to assist entry; however, this envelope is not the protein coat itself. The genome refers to the viral genetic material inside the capsid, and the nucleoid is a term used for bacterial chromosomal regions, not for viruses.