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The replication fork is a structure that forms within the long helical DNA during DNA replication. It is produced by enzymes called helicases that break the hydrogen bonds that hold the DNA strands together in a helix.
The process of semiconservative replication for the site of DNA replication is a fork-like DNA structure, the replication fork, where the DNA helix is open, or unwound, exposing unpaired DNA nucleotides for recognition and base pairing for the incorporation of free nucleotides into double-stranded DNA. [3]
The combination of template DNA and primer RNA is referred to as 'A-form DNA' and it is thought that clamp loading replication proteins (helical heteropentamers) want to associate with A-form DNA because of its shape (the structure of the major/minor groove) and chemistry (patterns of hydrogen bond donors and acceptors).
More than five decades ago, Jacob, Brenner, and Cuzin proposed the replicon hypothesis to explain the regulation of chromosomal DNA synthesis in E. coli. [18] The model postulates that a diffusible, trans-acting factor, a so-called initiator, interacts with a cis-acting DNA element, the replicator, to promote replication onset at a nearby origin.
A theta structure is an intermediate structure formed during the replication of a circular DNA molecule. Two replication forks can proceed independently around the DNA ring and when viewed from above the structure resembles the Greek letter "theta" (θ). [1] [2] Originally discovered by John Cairns, it led to the understanding that (in this ...
The double-helix model of DNA structure was first published in the journal Nature by James Watson and Francis Crick in 1953, [6] (X,Y,Z coordinates in 1954 [7]) based on the work of Rosalind Franklin and her student Raymond Gosling, who took the crucial X-ray diffraction image of DNA labeled as "Photo 51", [8] [9] and Maurice Wilkins, Alexander Stokes, and Herbert Wilson, [10] and base-pairing ...
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 ...
Some noncoding DNA sequences play structural roles in chromosomes. Telomeres and centromeres typically contain few genes but are important for the function and stability of chromosomes. [64] [102] An abundant form of noncoding DNA in humans are pseudogenes, which are copies of genes that have been disabled by mutation. [103]