What is the structure made up of proteins that serves as the outer coat of a virus?

The outer coat of a virus is specifically referred to as a capsid. This structure is composed of protein molecules that assemble into a protective shell, which encases the viral genetic material, whether it is DNA or RNA. The capsid plays a crucial role in protecting the viral genome from degradation and in facilitating the infection process by helping the virus attach to and enter host cells.

In contrast, while the term “protein coat” might seem somewhat related and may informally describe the capsid, it does not accurately reflect the standard terminology used in virology. The significance of the capsid is highlighted in its function and structure, as it is precise and widely recognized in scientific contexts.

The nucleoid refers to a region within a prokaryotic cell that contains genetic material, and it is not applicable to viruses. The envelope, on the other hand, refers to an additional lipid layer that some viruses possess outside the capsid. This envelope can help the virus evade the host immune response but is not the primary structure identified as the viral coat. Thus, the most accurate term for the outer structure of a virus is indeed the capsid.