Base Pair | Molecular Biology - Britannica

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External Websites

• Nature - Nature Communications - Shedding light on the base-pair opening dynamics of nucleic acids in living human cells
• Chemistry LibreTexts - DNA Base Pairs
• National Center for Biotechnology Information - PubMed Central - Model Systems for Understanding DNA Base Pairing

base pair molecular biology Ask Anything Homework Help Written by Justin Corfield Contributor to Encyclopedia of Global Health. He contributed several articles to SAGE Publications’ Encyclopedia of Governance (2007), which served as the basis for his contributions... Justin Corfield Fact-checked by Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Britannica Editors Last updated Dec. 15, 2025 •History Britannica AI Ask Anything Homework Help Table of Contents Table of Contents Ask Anything

base pair, in molecular biology, two complementary nitrogenous molecules that are connected by hydrogen bonds. Base pairs are found in double-stranded DNA and RNA, where the bonds between them connect the two strands, making the double-stranded structures possible. Base pairs themselves are formed from bases, which are complementary nitrogen-rich organic compounds known as purines or pyrimidines. According to Watson-Crick base-pairing, which forms the basis for the helical configuration of double-stranded DNA, DNA contains four bases: the two purines adenine (A) and guanine (G) and the two pyrimidines cytosine (C) and thymine (T). Within the DNA molecule, A bonds only with T and C bonds only with G. In RNA, thymine is replaced by uracil (U). Non-Watson-Crick base-pairing models display alternative hydrogen-bonding patterns; examples are Hoogsteen base pairs, which are A-T or C-G analogues.

Related Topics: nucleic acid (Show more) On the Web: Chemistry LibreTexts - DNA Base Pairs (Dec. 15, 2025) (Show more) See all related content

Base pairs often are used to measure the size of an individual gene within a DNA molecule. The total number of base pairs is equal to the number of nucleotides in one of the strands (each nucleotide consists of a base pair, a deoxyribose sugar, and a phosphate group). With extremely complex genomes, the detailing of base pairs can be complicated. The human genome, for example, is made up of an estimated three billion base pairs, with about 20,000 to 25,000 distinct genes. For dealing with those large numbers, scientists use measures such as kilobase pair (kb, or kbp), which is equivalent to 1,000 base pairs; megabase pair (Mb), which is equivalent to one million base pairs; and gigabase pair (Gb), which is equivalent to one billion base pairs.

Justin Corfield The Editors of Encyclopaedia Britannica