The smallest known infectious agent, consisting only of nucleic acid surrounded by a protein coat, is a(n) ________.

Nucleic Acid

A complex organic substance present in living cells, especially DNA or RNA, whose molecules consist of many nucleotides linked in a long chain.

Protein Coat

A protective layer surrounding the genetic material of a virus, known as a capsid, which helps in attaching the virus to host cells and facilitating viral entry.

Infectious Agent

A biological pathogen that has the ability to cause disease or illness in its host, including viruses, bacteria, fungi, and parasites.