Base pair

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In molecular biology and genetics, a base pair (or bp) represents the linking of two nitrogenous bases within a DNA double helix that are connected via hydrogen bonds. In the canonical Watson-Crick DNA base pairing, adenine (A) forms a base pair with thymine (T), and guanine (G) forms a base pair with cytosine (C).[1] In RNA, thymine is replaced by uracil (U). Alternate hydrogen bonding patterns, such as the wobble base pair and Hoogsteen base pair, also occur — in particular, in RNA — giving rise to complex and functional tertiary structures.[2] Pairing is the mechanism by which codons on messenger RNA molecules are recognized by anticodons on transfer RNA during protein translation. Some DNA- or RNA-binding enzymes can recognize specific base pairing patterns that identify particular regulatory regions of genes.

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).

Length measurements

The following abbreviations are commonly used to describe the length of a D/RNA molecule:

  • bp = base pair = one bp, which corresponds to approximately 3.4 Å of length along the strand's helix axis[3][1]
  • kb = kilo base pairs = 1,000 bp
  • Mb = mega base pairs = 1,000,000 bp
  • Gb = giga base pairs = 1,000,000,000 bp
  • Tb = tera base pairs = 1,000,000,000,000 bp

Note: In the case of single-stranded RNA, the unit of measure is the nucleotide (abbreviated nt, knt, Mnt, Gnt respectively), similar to how "base pair" is a length unit for double-stranded DNA. When making a distinction between units of computer storage and base pairs, kbp, Mbp, Gbp, etc. may be used for base pairs.


An element or two of this article is reused from the Wikipedia article.


  1. 1.0 1.1 Abouelmagd, Ahmed; Ageely, Hussein M. (2009). Basic Genetics: Textbook and Activities. Universal-Publishers. p. 87. ISBN 1599429039. Retrieved 30 September 2012. 
  2. Sinden, Richard R. (1994). DNA Structure and Function (2nd, illustrated, revised ed.). Gulf Professional Publishing. p. 15–21. ISBN 0126457506. Retrieved 30 September 2012. 
  3. Tropp, Burton E. (2011). Molecular Biology: Genes to Proteins (4th, revised ed.). Jones & Bartlett Publishers. p. 20. ISBN 0763786632. Retrieved 30 September 2012.