Editing DNA (section)

{{Short description|Molecule that carries genetic information}}
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{{For-multi|a non-technical introduction to the topic|Introduction to genetics|other uses}}
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{{Chromosome}}
[[File:DNA Structure+Key+Labelled.pn NoBB.png|thumb|right|upright=1.33|The structure of the DNA [[double helix]] (type [[B-DNA]]). The [[atom]]s in the structure are colour-coded by [[Chemical element|element]] and the detailed structures of two [[base pair]]s are shown in the bottom right.]][[File:Phosphate backbone.jpg|thumb|Simplified diagram]]
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'''Deoxyribonucleic acid''' ({{IPAc-en|audio=en-us-Deoxyribonucleic acid.ogg|d|iː|ˈ|ɒ|k|s|ᵻ|ˌ|r|aɪ|b|oʊ|nj|uː|ˌ|k|l|iː|ᵻ|k|,_|-|ˌ|k|l|eɪ|-}};<ref>{{MerriamWebsterDictionary|deoxyribonucleic acid}}</ref> '''DNA''') is a [[polymer]] composed of two [[polynucleotide]] chains that coil around each other to form a [[Nucleic acid double helix|double helix]]. The polymer carries [[genetics|genetic]] instructions for the development, functioning, growth and [[reproduction]] of all known [[organism]]s and many [[virus]]es. DNA and [[ribonucleic acid]] (RNA) are [[nucleic acid]]s. Alongside [[protein]]s, [[lipids]] and complex carbohydrates ([[polysaccharide]]s), nucleic acids are one of the four major types of [[macromolecule]]s that are essential for all known forms of [[life]].

The two DNA strands are known as polynucleotides as they are composed of simpler [[monomer]]ic units called [[nucleotide]]s.<ref>{{Cite book |vauthors= Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P |title= Molecular Biology of the Cell |edition= 6th |publisher= Garland |year= 2014 |url= http://www.garlandscience.com/product/isbn/9780815344322 |page= Chapter 4: DNA, Chromosomes and Genomes |isbn= 978-0-8153-4432-2 |url-status=live |archive-url= https://web.archive.org/web/20140714210549/http://www.garlandscience.com/product/isbn/9780815344322 |archive-date= 14 July 2014 |df= dmy-all }}</ref><ref>{{cite web | vauthors = Purcell A |title=DNA |url=http://basicbiology.net/micro/genetics/dna|website=Basic Biology |url-status=live |archive-url=https://web.archive.org/web/20170105045651/http://basicbiology.net/micro/genetics/dna/ |archive-date=5 January 2017}}</ref> Each nucleotide is composed of one of four [[nitrogenous base|nitrogen-containing]] [[nucleobase]]s ([[cytosine]] [C], [[guanine]] [G], [[adenine]] [A] or [[thymine]] [T]), a [[monosaccharide|sugar]] called [[deoxyribose]], and a [[Organophosphate|phosphate group]]. The nucleotides are joined to one another in a chain by [[covalent bond]]s (known as the [[Phosphodiester bond|phosphodiester linkage]]) between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating [[backbone chain|sugar-phosphate backbone]]. The nitrogenous bases of the two separate polynucleotide strands are bound together, according to [[base pair]]ing rules (A with T and C with G), with [[hydrogen bond]]s to make double-stranded DNA. The complementary nitrogenous bases are divided into two groups, the single-ringed [[pyrimidine]]s and the double-ringed [[purine]]s. In DNA, the pyrimidines are thymine and cytosine; the purines are adenine and guanine.

Both strands of double-stranded DNA store the same [[Central dogma of molecular biology#Biological sequence information|biological information]]. This information is [[DNA replication|replicated]] when the two strands separate. A large part of DNA (more than 98% for humans) is [[non-coding DNA|non-coding]], meaning that these sections do not serve as patterns for [[Primary protein structure|protein sequences]]. The two strands of DNA run in opposite directions to each other and are thus [[antiparallel (biochemistry)|antiparallel]]. Attached to each sugar is one of four types of nucleobases (or ''bases''). It is the [[Nucleic acid sequence|sequence]] of these four nucleobases along the backbone that encodes genetic information. RNA strands are created using DNA strands as a template in a process called [[transcription (genetics)|transcription]], where DNA bases are exchanged for their corresponding bases except in the case of thymine (T), for which RNA substitutes [[uracil]] (U).<ref>{{Cite web|url=https://www.genome.gov/genetics-glossary/Uracil|title=Uracil|website=Genome.gov|language=en|access-date=21 November 2019}}</ref> Under the [[genetic code]], these RNA strands specify the sequence of [[amino acid]]s within proteins in a process called [[translation (genetics)|translation]].

Within eukaryotic cells, DNA is organized into long structures called [[chromosome]]s. Before typical [[cell division]], these chromosomes are duplicated in the process of DNA replication, providing a complete set of chromosomes for each daughter cell. [[Eukaryote|Eukaryotic organisms]] ([[animal]]s, [[plant]]s, [[Fungus|fungi]] and [[protist]]s) store most of their DNA inside the [[cell nucleus]] as [[nuclear DNA]], and some in the [[mitochondrion|mitochondria]] as [[mitochondrial DNA]] or in [[chloroplast]]s as [[chloroplast DNA]].<ref>{{cite book | vauthors = Russell P | title= iGenetics |url= https://archive.org/details/igenetics0000russ_v6o1 |url-access= registration |publisher= Benjamin Cummings |location= New York |year= 2001 |isbn= 0-8053-4553-1}}</ref> In contrast, [[prokaryote]]s ([[bacteria]] and [[archaea]]) store their DNA only in the [[cytoplasm]], in [[circular chromosome]]s. Within eukaryotic chromosomes, [[chromatin]] proteins, such as [[histone]]s, compact and organize DNA. These compacting structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed.

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