DNA

Deoxyribonucleic acid ( /diːˌɒksɨˌraɪbɵ.n(j)uːˈkleɪ.ɪk ˈæsɪd/ (help·info)) (DNA) is anucleic acid that contains 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 ofblueprints, like 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 purposes, or are involved in regulating the use of this genetic information.

Chemically, DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars andphosphate 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 calledbases. It is the sequence of these four bases along the backbone that encodes information. This information is read using thegenetic code, which specifies the sequence of the amino acidswithin 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 long structures called chromosomes. These chromosomes are duplicated before cells divide, in a process called DNA replication. Eukaryotic organisms (animals,plants, fungi, and protists) store most of their DNA inside the cell nucleus and some of their DNA inorganelles, such as mitochondria or chloroplasts.^[1] In contrast, prokaryotes (bacteria and archaea) store their DNA only in the cytoplasm. Within the chromosomes, chromatin proteins such as histonescompact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed.