Complementarity (molecular biology)



In molecular biology, complementarity is a property of double-stranded nucleic acids such as DNA, as well as DNA:RNA duplexes. Each strand is complementary to the other in that the base pairs between them are non-covalently connected via two or three hydrogen bonds. For DNA, adenine (A) bases complement thymine (T) bases and vice versa; guanine (G) bases complement cytosine (C) bases and vice versa. With RNA, it is the same except that adenine (A) bases complement uracil (U) bases instead of thymine (T) bases.

Since there is only one complementary base for each of the bases found in DNA and in RNA, one can reconstruct a complementary strand for any single strand. All C bases in one strand will pair with G bases in the complementary strand, etc. This is essential for DNA replication.

For example, the complementary strand of the DNA sequence
 * 5' A G T C A T G 3'

is
 * 3' T C A G T A C 5'

Note that the latter is often written as the reverse complement with the 5' end on the left and the 3' end on the right
 * 5' C A T G A C T 3'

A sequence that is equal to its reverse complement is said to be a palindromic sequence.