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Deoxyribonucleic acid (DNA) is a molecule made up of two polynucleotide chains that coil around each other to create a double helix and carry genetic instructions for all known organisms and viruses’ formation, function, growth, and reproduction. Nucleic acids include DNA and ribonucleic acid (RNA). Nucleic acids are one of the four primary types of macromolecules that are required for all known forms of life, alongside proteins, lipids, and complex carbohydrates (polysaccharides).

Because they are made up of smaller monomeric units called nucleotides, the two DNA strands are known as polynucleotides. Each nucleotide is made up of a sugar termed deoxyribose, a phosphate group, and one of four nitrogen-containing nucleobases (cytosine, guanine, adenine, or thymine). Covalent connections (known as the phospho-diester linkage) between the sugar of one nucleotide and the phosphate of the next nucleotide bind the nucleotides together in a chain, resulting in an alternating sugar-phosphate backbone.

To create double-stranded DNA, the nitrogenous bases of the two distinct polynucleotide strands are linked together with hydrogen bonds according to base pairing regulations (A with T and C with G). Pyrimidines and purines are the two types of complimentary nitrogenous bases. Thymine and cytosine are pyrimidines in DNA, while adenine and guanine are purines.

The biological information is stored on both strands of double-stranded DNA. When the two strands split, this information is duplicated. Non-coding DNA makes up a substantial portion of DNA (more than 98 percent in humans), which means it does not serve as a blueprint for protein sequences. The two strands of DNA are antiparallel because they run in opposing directions.

Each sugar has one of four types of nucleobases attached to it (or bases). The genetic information is encoded by the sequence of these four nucleobases along the backbone. In a process known as transcription, RNA strands are produced using DNA strands as a template, with DNA bases being exchanged for their equivalent bases except for thymine (T), for which RNA replaces uracil (U). These RNA strands determine the sequence of amino acids within proteins in a process known as translation, which is controlled by the genetic code.

DNA is arranged into lengthy structures called chromosomes within eukaryotic cells. These chromosomes are replicated in the process of DNA replication before normal cell division, giving a complete set of chromosomes for each daughter cell. The majority of DNA in eukaryotic creatures (animals, plants, fungi, and protists) is stored in the cell nucleus as nuclear DNA, with some stored as mitochondrial DNA or chloroplast DNA.

Prokaryotes (bacteria and archaea), on the other hand, only store their DNA in the cytoplasm, in circular chromosomes. Chromatin proteins, such as histones, compress and arrange DNA within eukaryotic chromosomes. These compacting structures help regulate which portions of the DNA get transcribed by guiding the connections between DNA and other proteins.

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