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DNA
From Wikipedia, the free encyclopedia
For a non-technical introduction to the topic, see Introduction to genetics.
For other uses, see DNA (disambiguation).
The structure of the DNA double helix. The atoms in the structure are colour coded by element and the detailed structure of two base pairs is shown in the bottom right.
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The structure of part of a DNA double helixDeoxyribonucleic acid (/diˌɒksiˌraɪbɵ.njuːˌkleɪ.ɨk ˈæsɪd/ ( listen)), or DNA, is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms (with the exception of RNA viruses). The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of blueprints, like a recipe or a code, since itcontains 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. Along with RNA and proteins, DNA is one of the three major macromolecules that are essential for allknown forms of life.

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 nucleobases (informally, bases). It is the sequence of these four nucleobasesalong 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 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 in organelles, 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 histones compact and organize DNA.These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed.
Contents
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1 Properties
1.1 Grooves
1.2 Base pairing
1.3 Sense and antisense
1.4 Supercoiling
1.5 Alternate DNA structures
1.6 Alternate DNA chemistry
1.7 Quadruplex structures
1.8Branched DNA
1.9 Vibration
2 Chemical modifications
2.1 Base modifications
2.2 Damage
3 Biological functions
3.1 Genes and genomes
3.2 Transcription and translation
3.3 Replication
4 Interactions with proteins
4.1 DNA-binding proteins
4.2 DNA-modifying enzymes
4.2.1 Nucleases and ligases4.2.2 Topoisomerases and helicases
4.2.3 Polymerases
5 Genetic recombination
6 Evolution
7 Uses in technology
7.1 Genetic engineering
7.2 Forensics
7.3 Bioinformatics
7.4 DNA nanotechnology
7.5 History and anthropology
8 History of DNA research
9 See also
10 References
11 Further reading
12 Externallinks

Properties
Chemical structure of DNA. Hydrogen bonds shown as dotted lines.

DNA is a long polymer made from repeating units called nucleotides.[2][3][4] As first discovered by James D. Watson and Francis Crick, the structure of DNA of all species comprises two helical chains each coiled round the same axis, and each with a pitch of 34 Ångströms (3.4 nanometres) and a radius of 10...
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