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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 .
The chemical structure of DNA is insufficient to understand the complexity of the 3D structures of DNA. In contrast, animated molecular models allow one to visually explore the three-dimensional (3D) structure of DNA. The DNA model shown (far right) is a space-filling, or CPK, model of the DNA double helix. Animated molecular models, such as ...
DNA replication also works by using a DNA template, the DNA double helix unwinds during replication, exposing unpaired bases for new nucleotides to hydrogen bond to. Gene synthesis, however, does not require a DNA template and genes are assembled de novo. DNA synthesis occurs in all eukaryotes and prokaryotes, as well as some viruses. The ...
Since a sequence of single-stranded DNA needs to find its complementary strand to reform a double helix, common sequences renature more rapidly than rare sequences. Indeed, the rate at which a sequence will reassociate is proportional to the number of copies of that sequence in the DNA sample. A sample with a highly-repetitive sequence will ...
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 ...
Complementarity between two antiparallel strands of DNA. The top strand goes from the left to the right and the lower strand goes from the right to the left lining them up. Left: the nucleotide base pairs that can form in double-stranded DNA. Between A and T there are two hydrogen bonds, while there are three between C and G.
On contact with the intein-free copy, the HEG domain initiates the DNA double-stranded break repair mechanism. This process causes the intein sequence to be copied from the original source gene to the intein-free gene. This is an example of protein directly editing DNA sequence, as well as increasing the sequence's heritable propagation.
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.