Final answer:
The primary structure of a protein is least affected by a disruption in hydrogen bonding because it is maintained by covalent peptide bonds, which are not broken under conditions that disrupt weaker hydrogen bonds.
Step-by-step explanation:
The structural level of a protein least affected by a disruption in hydrogen bonding is the primary structure. This level of structure refers to the sequence of amino acids in the polypeptide chain, held together by peptide bonds, which are much stronger than hydrogen bonds. Despite the breaking of hydrogen bonds during denaturation, which will disrupt secondary, tertiary, and quaternary structures, the primary structure remains intact because the peptide bonds are not broken under conditions that disrupt hydrogen bonds. Therefore, the answer is a. the primary level.
The secondary structure is defined by the spatial arrangement of the polypeptide chain's backbone, primarily through hydrogen bonding, forming structures like α-helices and β-pleated sheets. Interruption of hydrogen bonding in this structure affects the correct folding and thus its stability and function.
Tertiary structure is the three-dimensional shape of a single polypeptide chain, stabilized by various interactions, including hydrogen bonds. Quaternary structure involves the interaction and assembly of multiple polypeptide subunits, which is also dependent on hydrogen bonds among other interactions for stability.
While all secondary, tertiary, and quaternary structures can be disrupted by the loss of hydrogen bonding, it is specifically the primary structure that will persist because its stability is owed to covalent peptide bonds.