In the ribonuclease experiment, which type of bond does urea break?

In the ribonuclease experiment, urea primarily disrupts hydrogen bonds. Urea is a chaotropic agent, meaning it can interfere with the stabilizing interactions that maintain the three-dimensional structure of proteins. In proteins, hydrogen bonds are crucial for stabilizing secondary and tertiary structures, such as alpha helices and beta sheets. By breaking these hydrogen bonds, urea unfolds the protein, allowing researchers to study its denatured state.

The other types of bonds in the options play different roles in protein structure. Disulfide bridges, formed between cysteine residues in proteins, contribute to the stability of the tertiary structure, but are not primarily affected by urea. Hydrophobic interactions, which occur between nonpolar side chains, also hold proteins in specific conformations, but are not directly broken down by urea; rather, these interactions are disrupted due to changes in the protein environment that urea creates. Ionic bonds involve interactions between charged side chains, and while they can be influenced by urea, the primary action of urea is its interaction with hydrogen bonding networks.