Base pair

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 bonds. 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 bonding patterns, "Watson–Crick" (or "Watson–Crick–Franklin") base pairs (guanine–cytosine and adenine–thymine)[1] allow the DNA helix to maintain a regular helical structure that is subtly dependent on its nucleotide sequence.[2] The complementary nature of this based-paired structure provides a 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 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 translated into the amino acid sequence of proteins 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 telomeres). The haploid human genome (23 chromosomes) is estimated to be about 3.2 billion base pairs long and to contain 20,000–25,000 distinct protein-coding genes.[3][4][5][6] A kilobase (kb) is a unit of measurement in molecular biology equal to 1000 base pairs of DNA or RNA.[7] The total number of DNA base pairs on Earth is estimated at 5.0×1037 with a weight of 50 billion tonnes.[8] In comparison, the total mass of the biosphere has been estimated to be as much as 4 TtC (trillion tons of carbon).[9]

  1. ^ Spencer M (10 January 1959). "The stereochemistry of deoxyribonucleic acid. II. Hydrogen-bonded pairs of bases". Acta Crystallographica. 12 (1): 66–71. doi:10.1107/S0365110X59000160. ISSN 0365-110X.
  2. ^ Zhurkin VB, Tolstorukov MY, Xu F, Colasanti AV, Olson WK (2005). "Sequence-Dependent Variability of B-DNA". DNA Conformation and Transcription. pp. 18–34. doi:10.1007/0-387-29148-2_2. ISBN 978-0-387-25579-8.
  3. ^ Moran LA (2011-03-24). "The total size of the human genome is very likely to be ~3,200 Mb". Sandwalk.blogspot.com. Retrieved 2012-07-16.
  4. ^ "The finished length of the human genome is 2.86 Gb". Strategicgenomics.com. 2006-06-12. Retrieved 2012-07-16.
  5. ^ "One copy of the human genome consists of approximately 3 billion base pairs of DNA". National Human Genome Research Institute. 2024-08-24.
  6. ^ International Human Genome Sequencing Consortium (October 2004). "Finishing the euchromatic sequence of the human genome". Nature. 431 (7011): 931–945. Bibcode:2004Natur.431..931H. doi:10.1038/nature03001. PMID 15496913.
  7. ^ Cockburn AF, Newkirk MJ, Firtel RA (December 1976). "Organization of the ribosomal RNA genes of Dictyostelium discoideum: mapping of the nontranscribed spacer regions". Cell. 9 (4 Pt 1): 605–613. doi:10.1016/0092-8674(76)90043-X. PMID 1034500. S2CID 31624366.
  8. ^ Nuwer R (18 July 2015). "Counting All the DNA on Earth". The New York Times. New York. ISSN 0362-4331. Archived from the original on 2022-01-01. Retrieved 2015-07-18.
  9. ^ "The Biosphere: Diversity of Life". Aspen Global Change Institute. Basalt, CO. Archived from the original on 2014-11-10. Retrieved 2015-07-19.