The structure of part of a DNA double helix
Deoxyribonucleic acid (DNA) is a nucleic acid that con-
tains the genetic instructions used in the development
and functioning of all known living organisms and some
viruses. The main role of DNA molecules is the long-
term storage of information. DNA is often compared to a
set of blueprints or a recipe, or a code, since it contains
the instructions needed to construct other components
of cells, such as proteins and RNA molecules. The DNA
segments that carry this genetic information are called
genes, but other DNA sequences have structural pur-
poses, or are involved in regulating the use of this genet-
Chemically, DNA consists of two long polymers of
simple units called nucleotides, with backbones made of
sugars and phosphate groups joined by ester bonds.
These two strands run in opposite directions to each
other and are therefore anti-parallel. Attached to each
sugar is one of four types of molecules called bases. It is
the sequence of these four bases along the backbone
that encodes information. This information is read using
the genetic code, which specifies the sequence of the
amino acids within proteins. The code is read by copying
stretches of DNA into the related nucleic acid RNA, in a
process called transcription.
Within cells, DNA is organized into structures called
chromosomes. These chromosomes are duplicated be-
fore cells divide, in a process called DNA replication.
Eukaryotic organisms (animals, plants, fungi, and prot-
ists) store their DNA inside the cell nucleus, while in
prokaryotes (bacteria and archaea) it is found in the
cell’s cytoplasm. Within the chromosomes, chromatin
proteins such as histones compact and organize DNA.
between DNA and other proteins, helping control which
parts of the DNA are transcribed.
DNA is a long polymer made from repeating units called
nucleotides. The DNA chain is 22 to 26 Ångströms
wide (2.2 to 2.6 nanometres), and one nucleotide un