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Purines form hydrogen bonds to pyrimidines, with adenine bonding only to thymine in two hydrogen bonds, and cytosine bonding only to guanine in three hydrogen bonds. This arrangement of two nucleotides binding together across the double helix (from six-carbon ring to six-carbon ring) is called a Watson-Crick base pair.
DNA is a macromolecule made up of nucleotide units, which are linked by covalent bonds and hydrogen bonds, in a repeating structure. DNA synthesis occurs when these nucleotide units are joined to form DNA; this can occur artificially (in vitro) or naturally (in vivo). Nucleotide units are made up of a nitrogenous base (cytosine, guanine ...
The chemical structure of DNA base-pairs . A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA and RNA.
In DNA double helix, the two strands of DNA are held together by hydrogen bonds. The nucleotides on one strand base pairs with the nucleotide on the other strand. The secondary structure is responsible for the shape that the nucleic acid assumes. The bases in the DNA are classified as purines and pyrimidines. The purines are adenine and guanine ...
The initial theory of hydrogen bonding proposed by Linus Pauling suggested that the hydrogen bonds had a partial covalent nature. This interpretation remained controversial until NMR techniques demonstrated information transfer between hydrogen-bonded nuclei, a feat that would only be possible if the hydrogen bond contained some covalent character.
The A–T pairing is based on two hydrogen bonds, while the C–G pairing is based on three. In both cases, the hydrogen bonds are between the amine and carbonyl groups on the complementary bases. Nucleobases such as adenine, guanine, xanthine , hypoxanthine , purine, 2,6-diaminopurine , and 6,8-diaminopurine may have formed in outer space as ...
Hoogsteen pointed out that if the alternative hydrogen-bonding patterns were present in DNA, then the double helix would have to assume a quite different shape. Hoogsteen base pairs are observed in alternative structures such as the four-stranded G-quadruplex structures that form in DNA and RNA.
Nucleobases are matched between strands through hydrogen bonds to form base pairs. Adenine pairs with thymine (two hydrogen bonds), and guanine pairs with cytosine (three hydrogen bonds). [18] DNA strands have a directionality, and the different ends of a single strand are called the "3′ (three-prime) end" and the "5′ (five-prime) end". By ...