tertiary structure

This term is a specialized technical expression used almost exclusively in biochemistry and molecular biology. It describes the final, functional shape of a protein, which is critical because the specific geometry determines how the protein interacts with other molecules. A failure in this folding process often leads to non-functional proteins or diseases, such as Alzheimer's.

In a linguistic sense, the term is a compound noun. While "structure" is generally countable, "tertiary structure" is typically treated as an uncountable concept when referring to the general state of folding, though it can be countable when discussing the specific structures of different proteins.