Florida Biology EOC Practice Test 2026 - Free Biology End-of-Course Practice Questions and Study Guide

The two strands of DNA are held together by hydrogen bonds, which are crucial for maintaining the double helix structure of DNA. These bonds form between complementary nitrogenous bases: adenine pairs with thymine and cytosine pairs with guanine. Each base pair is stabilized by hydrogen bonds, which allow the strands to separate easily during processes like DNA replication and transcription, yet remain intact during regular cellular functioning.

Covalent bonds, on the other hand, are present within each individual strand of DNA, linking the sugar and phosphate backbone together, but they do not hold the two strands together. Ionic bonds and Van der Waals forces are not involved in the stability of the DNA double helix structure. Therefore, hydrogen bonds are the primary force that keeps the strands of DNA together, facilitating both structural integrity and biological function.