Base pair

A base pair (bp) is a fundamental unit of double-stranded <a href="/facts/Nucleic_acids/2tTgcI0v">nucleic acids</a> consisting of two <a href="/facts/Nucleobases/zj1Vl9Qh">nucleobases</a> bound to each other by <a href="/facts/Hydrogen_bond/85V86IIg">hydrogen bonds</a>. They form the building blocks of the <a href="/facts/DNA/nB89Iauz">DNA</a> double helix and contribute to the folded structure of both DNA and <a href="/facts/RNA/HxPeNfNj">RNA</a>. Dictated by specific <a href="/facts/Hydrogen_bond/85V86IIg">hydrogen bonding</a> patterns, "Watson–Crick" (or "Watson–Crick–Franklin") base pairs (<a href="/facts/Guanine/hoTSpz0x">guanine</a>–<a href="/facts/Cytosine/JW20j33u">cytosine</a> and <a href="/facts/Adenine/PSeDFBnl">adenine</a>–<a href="/facts/Thymine/A5C8MnLN">thymine</a>) allow the DNA helix to maintain a regular helical structure that is subtly dependent on its <a href="/facts/Nucleotide_sequence/qAf4kTee">nucleotide sequence</a>. The <a href="/facts/Complementarity_(molecular_biology)/WQfqGlBJ">complementary</a> nature of this based-paired structure provides a <a href="/facts/Redundancy_(information_theory)/HnbfBLE0">redundant</a> copy of the <a href="/facts/Genetic_information/qAf4kTee">genetic information</a> 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 <a href="/facts/DNA_polymerase/xtNLncBu">DNA polymerase</a> replicates DNA and <a href="/facts/RNA_polymerase/gHd0ET9R">RNA polymerase</a> 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., <a href="/facts/Transfer_RNA/pR9T5XSl">transfer RNA</a>), where Watson–Crick base pairs (guanine–cytosine and adenine–<a href="/facts/Uracil/KUAcYYpQ">uracil</a>) 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 <a href="/facts/RNA_structure/U7sYh5pn">structures</a>. In addition, base-pairing between <a href="/facts/Transfer_RNA/pR9T5XSl">transfer RNA</a> (tRNA) and <a href="/facts/Messenger_RNA/oUL6qxQn">messenger RNA</a> (mRNA) forms the basis for the <a href="/facts/Molecular_recognition/a3QRaYN4">molecular recognition</a> events that result in the nucleotide sequence of mRNA becoming <a href="/facts/Genetic_code/zUK0bY1B">translated</a> into the amino acid sequence of <a href="/facts/Protein/Jxmagu3E">proteins</a> via the <a href="/facts/Genetic_code/zUK0bY1B">genetic code</a>.
The size of an individual <a href="/facts/Gene/e1swwPY6">gene</a> or an organism's entire <a href="/facts/Genome/31Sm08JT">genome</a> 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 <a href="/facts/Telomere/RQ4Gp9LT">telomeres</a>). The <a href="/facts/Haploid/U8zl4AQe">haploid</a> <a href="/facts/Human_genome/VTV85pbn">human genome</a> (23 <a href="/facts/Chromosome/FRGf11FC">chromosomes</a>) is estimated to be about 3.2 billion base pairs long and to contain 20,000–25,000 distinct protein-coding genes. A <a href="/facts/Kilobase/xmPpPQ9W">kilobase</a> (kb) is a unit of measurement in <a href="/facts/Molecular_biology/YgqU35ub">molecular biology</a> equal to 1000 base pairs of DNA or RNA. The total number of <a href="/facts/DNA/nB89Iauz">DNA</a> base pairs on Earth is estimated at 5.0×1037 with a weight of 50 billion <a href="/facts/Tonne/gMymLmWv">tonnes</a>. In comparison, the total <a href="/facts/Biomass_(ecology)/A5rDsUax">mass</a> of the <a href="/facts/Biosphere/P1ltA4sb">biosphere</a> has been estimated to be as much as 4 <a href="/facts/Tonnes/gMymLmWv">TtC</a> (trillion tons of <a href="/facts/Carbon/ukrgQexo">carbon</a>).

Base pair open-in-new

Base pair