Editing Base pair (section)

{{Short description|Two nucleobases bound by hydrogen bonds}}
[[File:DNA base-pair diagram.jpg|thumb|upright=1.4|The chemical structure of DNA base-pairs  ]]
A '''base pair''' ('''bp''') is a fundamental unit of double-stranded [[nucleic acids]] consisting of two [[nucleobases]] bound to each other by [[hydrogen bond]]s.  They form the building blocks of the [[DNA]] double helix and contribute to the folded structure of both DNA and [[RNA]]. Dictated by specific [[hydrogen bond]]ing patterns, "Watson–Crick" (or "Watson–Crick–Franklin") base pairs ([[guanine]]–[[cytosine]] and [[adenine]]–[[thymine]])<ref>{{cite journal | vauthors = Spencer M |title=The stereochemistry of deoxyribonucleic acid. II. Hydrogen-bonded pairs of bases |journal=Acta Crystallographica |date=10 January 1959 |volume=12 |issue=1 |pages=66–71 |doi=10.1107/S0365110X59000160 |url=https://scripts.iucr.org/cgi-bin/paper?S0365110X59000160 |language=en |issn=0365-110X|url-access=subscription }}</ref> allow the DNA helix to maintain a regular helical structure that is subtly dependent on its [[nucleotide sequence]].<ref>{{Cite book |chapter=Sequence-Dependent Variability of B-DNA | doi=10.1007/0-387-29148-2_2 | title=DNA Conformation and Transcription |pages=18–34 |year=2005 | vauthors = Zhurkin VB, Tolstorukov MY, Xu F, Colasanti AV, Olson WK  | isbn=978-0-387-25579-8 }}</ref> The [[Complementarity (molecular biology)|complementary]] nature of this based-paired structure provides a [[Redundancy (information theory)|redundant]] copy of the [[genetic information]] encoded within each strand of DNA. The regular structure and data redundancy provided by the DNA double helix make DNA well suited to the storage of genetic information, while base-pairing between DNA and incoming nucleotides provides the mechanism through which [[DNA polymerase]] replicates DNA and [[RNA polymerase]] transcribes DNA into RNA. Many DNA-binding proteins can recognize specific base-pairing patterns that identify particular regulatory regions of genes.

Intramolecular base pairs can occur within single-stranded nucleic acids. This is particularly important in RNA molecules (e.g., [[transfer RNA]]), where Watson–Crick base pairs (guanine–cytosine and adenine–[[uracil]]) permit the formation of short double-stranded helices, and a wide variety of non–Watson–Crick interactions (e.g., G–U or A–A) allow RNAs to fold into a vast range of specific three-dimensional [[RNA structure|structures]]. In addition, base-pairing between [[transfer RNA]] (tRNA) and [[messenger RNA]] (mRNA) forms the basis for the [[molecular recognition]] events that result in the nucleotide sequence of mRNA becoming [[Genetic code|translated]] into the amino acid sequence of [[protein]]s via the [[genetic code]].

The size of an individual [[gene]] or an organism's entire [[genome]] is often measured in base pairs because DNA is usually double-stranded. Hence, the number of total base pairs is equal to the number of nucleotides in one of the strands (with the exception of non-coding single-stranded regions of [[telomere]]s). The [[haploid]] [[human genome]] (23 [[chromosome]]s) is estimated to be about 3.2 billion base pairs long and to contain 20,000–25,000 distinct protein-coding genes.<ref>{{cite web | vauthors = Moran LA |url=http://sandwalk.blogspot.com/2011/03/how-big-is-human-genome.html |title=The total size of the human genome is very likely to be ~3,200 Mb |publisher=Sandwalk.blogspot.com |date=2011-03-24 |access-date=2012-07-16}}</ref><ref>{{cite web |url=http://www.strategicgenomics.com/Genome/index.htm |title=The finished length of the human genome is 2.86 Gb |publisher=Strategicgenomics.com |date=2006-06-12 |access-date=2012-07-16}}</ref><ref>{{cite web |url=https://www.genome.gov/genetics-glossary/Base-Pair |title=One copy of the human genome consists of approximately 3 billion base pairs of DNA |publisher=National Human Genome Research Institute |date=2024-08-24}}</ref><ref name="IHSGC2004">{{cite journal | vauthors = ((International Human Genome Sequencing Consortium)) | title = Finishing the euchromatic sequence of the human genome | journal = Nature | volume = 431 | issue = 7011 | pages = 931–945 | date = October 2004 | pmid = 15496913 | doi = 10.1038/nature03001 | doi-access = free | bibcode = 2004Natur.431..931H }}</ref> A [[kilobase]] (kb) is a unit of measurement in [[molecular biology]] equal to 1000 base pairs of DNA or RNA.<ref>{{cite journal | vauthors = Cockburn AF, Newkirk MJ, Firtel RA | title = Organization of the ribosomal RNA genes of Dictyostelium discoideum: mapping of the nontranscribed spacer regions | journal = Cell | volume = 9 | issue = 4 Pt 1 | pages = 605–613 | date = December 1976 | pmid = 1034500 | doi = 10.1016/0092-8674(76)90043-X | s2cid = 31624366 }}</ref> The total number of [[DNA]] base pairs on Earth is estimated at 5.0{{e|37}} with a weight of 50 billion [[tonne]]s.<ref name="NYT-20150718-rn">{{cite news | vauthors = Nuwer R |author-link=Rachel Nuwer |date=18 July 2015 |title=Counting All the DNA on Earth |url=https://www.nytimes.com/2015/07/21/science/counting-all-the-dna-on-earth.html |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2015/07/21/science/counting-all-the-dna-on-earth.html |archive-date=2022-01-01 |url-access=limited |work=The New York Times |location=New York |issn=0362-4331 |access-date=2015-07-18}}{{cbignore}}</ref><!--- PLOS paper cited by NYT used 'tonne' unit. ---> In comparison, the total [[Biomass (ecology)|mass]] of the [[biosphere]] has been estimated to be as much as 4&nbsp;[[tonnes#Derived units|TtC]] (trillion tons of [[carbon]]).<ref name="AGCI-2015">{{cite web |url=http://www.agci.org/classroom/biosphere/index.php |title=The Biosphere: Diversity of Life |author=<!--Staff writer(s); no by-line.--> |website=Aspen Global Change Institute |location=Basalt, CO |access-date=2015-07-19 |archive-date=2014-11-10 |archive-url=https://web.archive.org/web/20141110164609/http://www.agci.org/classroom/biosphere/index.php |url-status=dead }}</ref><!--- Aspen Global Change Institute (US-based) defined TtC as 'trillion tons of C'. --->