Here's why:

* Nucleic acid: Viruses contain either DNA or RNA as their genetic material.

* Protein coat (capsid): This protein shell surrounds the nucleic acid, protecting it and enabling the virus to attach to and enter host cells.

While viruses are often described as being "coated" in protein, it's important to understand that the capsid isn't simply a layer on the outside. The protein molecules are arranged in a specific, complex structure that interacts with the nucleic acid inside.

Let me know if you'd like to learn more about the different types of viral capsids or how viruses infect cells!