base pair

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A pair of nitrogenous bases, consisting of a purine linked by hydrogen bonds to a pyrimidine, that connects the complementary strands of DNA or of hybrid molecules joining DNA and RNA. The base pairs are adenine-thymine and guanine-cytosine in DNA, and adenine-uracil and guanine-cytosine in RNA.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Biochemistry, Genetics) a unit of double-stranded DNA or RNA consisting of two complementary bases on opposing strands of the double-stranded polynucleotide, bound together by hydrogen bonds and other non-covalent chemical forces. The bases comprising the base pairs are adenine, thymine, cytidine, and guanine. In normal DNA, the base adenine on one strand of DNA pairs with thymine on the opposite strand, and cytosine on one strand pairs with guanine on the opposite strand. The term base pair usually includes the sugar (ribose or deoxyribose) and the phosphate bound to each base to form a nucleotide unit. One base pair is sometimes used as a unit of length or size for DNA, and in this usage is abbreviated bp. A length of 1000 base pairs is a kilobase pair or kbp.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun biology In molecular biology, two nucleotides on opposite complementary DNA or RNA strands that are connected via hydrogen bonds.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun one of the pairs of chemical bases joined by hydrogen bonds that connect the complementary strands of a DNA molecule or of an RNA molecule that has two strands; the base pairs are adenine with thymine and guanine with cytosine in DNA and adenine with uracil and guanine with cytosine in RNA