By Noelle Carver – Updated March 24, 2022
Jason Reed/Photodisc/Getty Images
The deoxyribonucleic acid (DNA) molecule is a double‑helical “twisted ladder.” Each rung of this ladder is composed of a nucleotide, which contains a sugar, a phosphate group, and one of four nitrogenous bases. Understanding the arrangement of these bases is key to grasping how DNA encodes genetic information.
Each strand of DNA is a sequence of the four bases: Adenine (A), Cytosine (C), Guanine (G), and Thymine (T). Adenine and Guanine are purines (double‑ring structures), while Cytosine and Thymine are pyrimidines (single‑ring structures). Base‑pairing rules dictate that A pairs with T and C pairs with G via hydrogen bonds. In your model, label each rung with its corresponding complementary pair.
Between the two bases of a rung lie the hydrogen bonds that stabilize the helix. Mark these bonds on your diagram or physical model to illustrate the inter‑strand connections.
The two long strands that form the sides of the ladder are the sugar‑phosphate backbone. Use a distinct color or label to highlight this structural framework.
Triplets of bases—such as ATG, CTC, GAA—form codons, the “words” of the genetic language. Sequences of codons create genes, the “sentences” that dictate cellular function.
