Nucleic acids deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the genetic material of cells. Their names are derived from the type of sugar, ribose, contained within these molecules.

Phosphate-Sugar Backbone

Nucleotides linked together by covalent bonds between the phosphate of one nucleotide and the sugar of next. These linked monomers become the phosphate-sugar backbone of nucleic acids. Nitrogenous bases extending from this phosphate-sugar backbone like teeth of a comb.

The Twisted “Ladder” of Nucleic Acid

Hydrogen bonds form between specific bases of two nucleic acid chains, forming a stable, double-stranded DNA molecule, which looks like a ladder. Three H bonds form between bases cytosine (C) and guanine (G), which always pair up together between two nucleic acid chains. Two H bonds form between adenine (A) and thymine (T) in DNA or adenine and uracil (U) in RNA molecules.

The structure is analogous to a ladder, with the two deoxyribose-phosphate chains as side rails and the base pairs, linked by hydrogen bonds, forming the rungs. Hydrogen bonding also twists the phosphate-deoxyribose backbones into a helix, thus typical DNA is a double helix.
Additional Organic Chemistry Resources

To learn more about cell biology and organic chemisty and molecules, see the Suite101 articles What Is a Lipid, Amino Acids & Proteins, What Is a Carbohydrate and What Are Organic Molecules. Other excellent sites for information on organic chemistry include Science Prof Online and the Organic Chemistry Help site.