DNA (IMAGE) University of California - Santa Barbara Caption One example of how hydrophobic interactions are critical to biomedical applications can be found in how DNA base pairs on the two strands are drawn together to form a double helix. The basic structure of a DNA molecule is a hydrophilic backbone and a hydrophobic inner region of nitrogenous bases (adenine, guanine, thymine, and cytosine). These molecular hydrophobic forces repel the water between them which drives the bases towards each other. Credit UCSB Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.