DNA [Structures]
DNA is composed of many deoxynucleotidyl residues each other with a certain amount of order 3 ', 5'-phosphate ester bond linked to a long chain. Most of DNA containing two such long-chain, and some are single DNA chain, such as E. coli φ X174 bacteriophage, G4, such as M13. Some DNA for the ring, and some of linear DNA. Main contain adenine, guanine, thymine and cytosine four kinds of bases. In certain types of DNA, 5 - methylcytosine within certain limits can be replaced by cytosine, which the wheat germ DNA 5 - methylcytosine particularly rich, Moore is 6%. In some phage, 5 - hydroxymethyl-cytosine replaced cytosine. 40 late 1990s, Mrs. investigation (E. Chargaff) found that different species of DNA base composition different, but equivalent to the number of its thymine adenine (A = T), cytosine guanine few equivalent ( G = C), thus the number of purine and pyrimidine equivalent to the sum of the number. Several described by the general level of the structure of DNA.
A structure of a DNA structure that is the sequence. Gene is a fragment of DNA, the genetic information stored in their genetic sequence of. 1975 United States Gilbert (W. Gilbert) and the United Kingdom's Sanger (F. Sanger) were the creation of a DNA structure of the rapid determination of their total for the year 1980 Nobel Prize in Chemistry. Since then, determination and constantly improved, many of the level structure of DNA has been established. If people ring of mitochondrial DNA containing 16,569 base pairs, λ phage DNA containing 48,502 base pairs, rice chloroplast genome of 134,525 base pairs, tobacco chloroplast genome of 155,844 base pairs, etc.. Now the United States has plans to 10 to 15 years in all of human DNA molecule of about 3 billion nucleotide sequencing out of.
Secondary structure in 1953, Watson (Watson) and Crick (Crick) of the basic structure of DNA fibers is the double helix structure of this model was recognized by scientists, and to explain replication, transcription, and other important life process. After in-depth study and found that due to humidity and different conditions, such as sequence, DNA double helix can have many types, mainly divided into A, B and Z3 major categories.
Generally believed that the nearest B configuration of the DNA in cells of conformation, and the double helix model it is very similar. A-DNA and RNA molecules in the area, as well as the double helix of DNA was formed in transcription-RNA hybrid molecular conformation close. Z-DNA nucleotide dimer in the unit left to the wound, its main chain were serrated (Z)-, Gu Ming. This configuration suitable for multi-pyrimidine nucleotides chain of alternating purine District. 1989, the United States scientists using scanning tunneling electron microscope to directly observe the DNA double helix DNA double helix: in 1952, Austria-American biochemists search Jiafu (E.chargaff, 1905 -) Determination of the DNA of the four kinds of bases Content found gland fat methotrexate and the same number of thymine, cytosine birds fat and the number of methotrexate equal. This makes Watson, Crick immediately think of four kinds of bases exist between February 2 corresponding relations, and formed a gland fat methotrexate paired with thymine, cytosine and bird fat methotrexate matching concept.
February 1953, Watson, Crick saw through Weierjinshi Franklin in November 1951 shooting of a very beautiful DNA crystal X-ray diffraction photos, to stimulate their inspiration. They not only confirmed the DNA helix structure is certain, and that the spiral of parameters. They used the rich Lankelin and Wilkins judgement, and to add: phosphate in a spiral of more than two lateral nucleotide chain skeleton, the opposite direction; base in the inner spiral, February 2 counterparts.
Over the past few days, Watson and Crick in their offices happily with a tin and wire model structures. February 28, 1953, a DNA double helix structure of the molecular model was born.
Double helix model of significance, not only proven means that the structure of the DNA molecule, it is more important that a mechanism of DNA replication: As always with methotrexate gland fat thymidine matching, the birds fat methotrexate always paired with cytosine This shows that the two chains base sequence complementary to each other, identified as one of the nucleotide sequence chain, another chain will determine the base sequence. Therefore, only one of them linked to the template can be copied to another of a chain.
Kerik from the beginning to insist that in the April 25 papers published in the "specific DNA matching principle, immediately reminiscent of genetic material may have to copy mechanisms" such a statement. He believes that if no such sentence would mean he and Watson "lack of insight, which can not be seen to this point."
In a DNA double helix structure papers shortly after, the "natural" Shortly afterward magazine also published a paper Kerik another, a semi-stated reservations DNA replication mechanism.
Monday, April 21, 2008
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