Question

Which statement about protein stability and denaturation is incorrect?

a) Proteins can be denatured by significant changes in pH since this affects stabilizing electrostatic interactions.

b) Denaturants such as urea and guanidinium hydrochloride are used to denature proteins.

c) Hydrolytic enzymes, such as proteases, cleave the backbone peptide bonds of proteins, which alters the primary structure of the protein.

d) Proteins can be denatured by heat since this affects covalent peptide bonds.

e) An inactive protein is still folded but has undergone small conformational changes from the native state, making it unable to catalyze reactions.

Answer 1

Statement d is incorrect because heat denatures proteins by disrupting non-covalent bonds and interactions, not the covalent peptide bonds in the primary structure. Denaturation involves changes to a protein's shape without altering its amino acid sequence unless hydrolysis occurs, which is not a denaturation process.

Step-by-step explanation:

The incorrect statement about protein stability and denaturation is: d) Proteins can be denatured by heat since this affects covalent peptide bonds. Heat causes denaturation by disrupting the non-covalent bonds and interactions that maintain the protein's tertiary and secondary structures, not the primary structure's covalent peptide bonds.

Proteins are made up of chains of amino acids with a unique sequence (primary structure) that fold into complex three-dimensional shapes (secondary, tertiary, and quaternary structures) critical for their function. Various agents and conditions such as significant changes in pH, denaturants like urea and guanidinium hydrochloride, and heat can cause protein denaturation. However, this process typically does not break the covalent bonds within the primary structure unless under extreme conditions.

Hydrolytic enzymes, like proteases, can alter a protein's primary structure by cleaving its backbone peptide bonds, but this is not denaturation—it is hydrolysis. A denatured protein can sometimes return to its native state when the denaturing agent is removed, provided its primary sequence remains intact. However, denaturation can also be irreversible, for example, when cooking an egg white.