American Chemical Society (ACS) Chemistry Practice Exam – Practice Test & Study Guide

The structure of proteins and DNA is primarily stabilized by hydrogen bonds. In proteins, these bonds help maintain the secondary structure, such as alpha helices and beta sheets, by forming interactions between the backbone amide groups and carbonyl groups. In the case of DNA, hydrogen bonds play a crucial role in holding the two strands of the double helix together, specifically between the nitrogenous bases—adenine pairs with thymine via two hydrogen bonds, while cytosine pairs with guanine through three hydrogen bonds.

While covalent bonds are essential for linking amino acids in proteins (through peptide bonds) and connecting the sugar and phosphate in the DNA backbone, they do not provide the same dynamic stability as hydrogen bonds. Ionic bonds contribute to protein structure and stability through interactions between charged side chains but are not the primary stabilizing force. Metallic bonds do not pertain to the structural makeup of proteins or DNA. Thus, hydrogen bonds are key in providing the necessary stability and flexibility for both proteins and DNA, making them the correct choice.