Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are two types of macromolecules that play a role in the genetic makeup of living things.
Nucleic acids, such as deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are composed of smaller subunits called nucleotides. They have a sugar-phosphate backbone and can be single or double stranded. A nucleotide is an organic compound composed of three parts: a sugar (either ribose or deoxyribose), at least one phosphate group, and a nitrogen-containing base. The base can have a single- or double-ring structure. Nucleotides have many functions. In addition to acting as the building blocks for nucleic acids, nucleotides can act as energy carriers, as coenzymes, and as chemical messengers.
DNA is a double-stranded molecule that consists of four types of nucleotides: adenine, thymine, guanine, and cytosine. RNA is usually single stranded and also consists of four types of nucleotides. Deoxyribose is different from the ribose sugar in RNA, as the 2′ hydroxyl group is replaced with a hydrogen. Unlike DNA, RNA contains the nitrogenous base uracil, in place of thymine. Like protein synthesis, the process of DNA and RNA synthesis from nucleotides occurs via a series of condensation reactions. Several nucleotides bond together through the formation of phosphate ester linkages. This happens when the hydroxyl group of a phosphate from one nucleotide participates in a condensation reaction with the hydroxyl group on the carbohydrate ring from a different nucleotide. As this reaction proceeds, nucleotides link together, forming a nucleic acid molecule. In terms of structure, the 5′ and 3′ end of carbons attached to the ribose of DNA and RNA are essential in forming backbones for both nucleic acid structures. The nitrogenous base, part of this nucleic acid structure, is free to pair with its complement base. That is, the nitrogenous base adenine can pair with its complement thymine while cytosine pairs with guanine.