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In molecular biology, the term double helix [1] refers to the structure formed by double-stranded molecules of nucleic acids such as DNA. The double helical structure of a nucleic acid complex arises as a consequence of its secondary structure , and is a fundamental component in determining its tertiary structure .
A distinct group of DNA-binding proteins is the DNA-binding proteins that specifically bind single-stranded DNA. In humans, replication protein A is the best-understood member of this family and is used in processes where the double helix is separated, including DNA replication, recombination, and DNA repair. [ 123 ]
Structure of double-stranded DNA, the product of DNA synthesis, showing individual nucleotide units and bonds. DNA synthesis is the natural or artificial creation of deoxyribonucleic acid (DNA) molecules. DNA is a macromolecule made up of nucleotide units, which are
DNA exists as a double-stranded structure, with both strands coiled together to form the characteristic double helix. Each single strand of DNA is a chain of four types of nucleotides. Nucleotides in DNA contain a deoxyribose sugar, a phosphate, and a nucleobase.
In most cases, naturally occurring DNA molecules are double-stranded and RNA molecules are single-stranded. [19] There are numerous exceptions, however—some viruses have genomes made of double-stranded RNA and other viruses have single-stranded DNA genomes, [20] and, in some circumstances, nucleic acid structures with three or four strands ...
When a molecule of DNA is double stranded, as DNA usually is, the two strands run in opposite directions. Therefore, one end of the molecule will have the 3' end of strand 1 and the 5' end of strand 2, and vice versa in the other end. [2] However, the fact that the molecule is two stranded allows numerous different variations.
The tertiary arrangement of DNA's double helix in space includes B-DNA, A-DNA, and Z-DNA. Triple-stranded DNA structures have been demonstrated in repetitive polypurine:polypyrimidine Microsatellite sequences and Satellite DNA. B-DNA is the most common form of DNA in vivo and is a more narrow, elongated helix than A-DNA. Its wide major groove ...
To synthesize DNA, the double-stranded DNA is unwound by DNA helicases ahead of polymerases, forming a replication fork containing two single-stranded templates. Replication processes permit copying a single DNA double helix into two DNA helices, which are divided into the daughter cells at mitosis.