Final answer:
A fully folded, functional protein with all subunits intact is in its native folded state. Denaturation, often caused by changes in temperature, pH, or chemicals, can lead to reversible or irreversible loss of protein function. The term 'native folded' contrasts with a denatured state, where a protein loses its higher-order structure but maintains its primary sequence of amino acids.
Step-by-step explanation:
The protein in its intact, fully functional form, fully folded with all subunits intact if it is multimeric, would be considered in its native folded state. The process that leads to a protein assuming a three-dimensional structure, which is critical to its function, is called protein folding. A protein's native structure is its functional form that has the secondary, tertiary, and possibly quaternary structure intact. This structurally integral form contrasts with the denatured state where a protein loses these higher-order structures and often, its biological function. It's important to note that such denaturing conditions do not affect the protein's primary structure—that is, the sequence of amino acids in the polypeptide chain remains unchanged.
Under certain conditions, such as changes in temperature, pH, or chemical exposure, denaturation can occur. However, this process is sometimes reversible, allowing the protein to refold and regain its function. If the denaturing agent is removed, the preserved primary structure can allow the protein to resume its function. Yet, it's also possible for denaturation to be irreversible, resulting in a permanent loss of a protein's function. An example of this is the cooking of egg whites where the albumin protein becomes denatured.