Identify the incorrect  statements about  tertiary structure of proteins?

To identify the incorrect statement about the tertiary structure of proteins, we examine each statement based on the structural features and stabilizing forces involved in protein folding.

The tertiary structure of a protein represents the overall three-dimensional folding of a polypeptide chain and may adopt either a fibrous or globular form. Therefore, the statement that it can be fibrous or globular in structure is correct.

The tertiary structure is stabilized by several interactions, including hydrogen bonding, disulphide linkages, van der Waals forces, and electrostatic interactions between amino acid side chains. Hence, this statement is also correct.

The statement that the tertiary structure remains intact when exposed to pH changes is incorrect. Changes in pH alter the ionization states of amino acid side chains, disrupting ionic interactions and hydrogen bonds that stabilize the protein. As a result, the protein may undergo denaturation, losing its native three-dimensional structure.

Protein folding follows a hierarchical organization in which the linear polypeptide chain (primary structure) first forms secondary structures such as $$\alpha$$-helices and $$\beta$$-pleated sheets, and further folding of these secondary structures gives rise to the tertiary structure. Therefore, this statement is correct.

Hence, the incorrect statement is Option C, since the tertiary structure of proteins does not remain intact when exposed to significant changes in pH.