Base pair

As a base pair is called two nucleobases in DNA or RNA that are complementary to each other and are held together by hydrogen bonds. The number of base pairs of the gene is an important measure of the information that is stored in the gene. It is in

  • Kbp or kb = kilo base pairs ( 1000 base pairs ) was measured.

The lengths for larger DNA segments are also

A bp corresponds to a quantity of information of 2 bits, as it may represent four different values. A base pair has thus double the information density of the binary code.

Importance of base pairs

Base pairing plays a significant role in the DNA replication, transcription and translation of the protein in the course of, as well as for a variety of configurations of the tertiary structure of nucleic acids.

  • Replication: The new nucleotide strands obtained by base-pairing the complementary base sequence to the two template strands.
  • Transcription: mRNA, tRNA and rRNA obtained by base pairing to the codogenic strand of DNA complementary base sequence, where A is paired with U.
  • The three bases of the anticodon of tRNAs pair with the complementary base triplet of the mRNA. This results in the encoded amino acid from the DNA sequence of the proteins. Here come the wobble pairings in the pairing of the third base of a codon of the mRNA with the first base of the tRNA.

Pairing rules

Basically always a purine base (guanine or adenine) with a pyrimidine (cytosine or thymine or uracil ) form exactly one base pair.

This yields the following pairings result:


  • A-T (adenine and thymine )
  • G -C ( guanine and cytosine)


  • A- U ( adenine and uracil)
  • G -C ( guanine and cytosine)

Watson -Crick pairings

Already 1949, biochemist Erwin Chargaff, the Austrian states that in DNA the number of the bases adenine (A) and thymine (T ) is always in the ratio 1: 1 is present, as the ratio of the bases guanine ( G) and cytosine ( C) 1: G or C: T strong ( Chargaff'sche rules ) 1 In contrast, the amount ratio A varies.

This included James D. Watson and Francis Harry Compton Crick that AT and GC each form complementary base pairs.

In the tRNA and rRNA base pairings also occur when the nucleotide strand forming loops and thereby facing complementary base sequences. Since in RNA instead of thymine only uracil is incorporated, are the pairs AU and GC.

Unusual pairings

Unusual pairings occur mainly in tRNAs and in triple helices. While you follow the Watson -Crick scheme, but form other hydrogen bonds from: examples are reverse Watson -Crick pairing, Hoogsteen pairs (named after Karst Hoogsteen, born 1923) and reverse - Hoogsteen pairings

Wobble pairings

The term refers to the wobble hypothesis of Francis Crick ( 1966). Wobble pairings are not Watson -Crick pairings GU or GT and AC: