structure of DNA

DNA is composed of many deoxynucleotidyl residues with each other by a certain order of 3 ', 5'-phosphate ester bond linked to a long chain. Most of DNA containing two such long-chain, and some DNA for single-chain, such as E. coli phage φ X174, G4, M13, and so on. Some DNA for the ring, some for the linear DNA. Mainly with adenine, guanine, thymine and cytosine four kinds of bases. In some types of DNA, 5 - cytosine-to a certain extent can replace the CD, wheat germ DNA of 5 - methyl cytosine particularly rich, up 6 percent Moore. In some phage, 5 - hydroxymethyl cytosine replaced the CD. The late 1940s, Chargaff (E. Chargaff) found that different species of DNA base pairs of different, but the number of adenine equivalent to the number of its thymine (A = T), guanine cytosine equal to the number of (G = C), and thus the number of purine equivalent to the number of and pyrimidine. General painted with several levels of DNA structure. A structure of DNA in a structure that is its base sequence. Gene is a fragment of DNA, the genetic information stored in its genetic sequence of. 1975 U.S. Gilbert (W. Gilbert) and the United Kingdom Sanger (F. Sanger) respectively, created the structure of DNA a rapid determination of their total for the year 1980 Nobel Prize in Chemistry. Since then, determination and constantly improved, many of the DNA structure of an established. If people ring of mitochondrial DNA contains 16,569 base pairs, λ phage containing 48,502 DNA base pairs, rice chloroplast genome of 134,525 base pairs, tobacco chloroplast genome of 155,844 base pairs, and so on. Now the U.S. has plans to 10-15 years in all human DNA molecule of about 3 billion nucleotide pairs out of sequence. Secondary structure in 1953, Watson (Watson) and Crick (Crick) to the basic structure of DNA fibers is the double helix structure, but this model, the scientists acknowledged, and to explain reproduction, transcription and other important life process. After in-depth study and found that because of humidity and the base sequence of different conditions, DNA double helix can have many types, mainly divided into A, B and Z three categories. Is generally believed that, B configuration of the nearest cell in the DNA conformation, it is the double helix model is very similar. A-DNA and RNA molecules in the double helix, as well as the formation of transcription, DNA-RNA hybrid molecular conformation close. Z-DNA nucleotide dimer as a unit to the left to the winding, its main chain was serrated (Z) form, Gu Ming. This configuration of the chain for more than purine nucleotide pyrimidine alternate area. 1989, U.S. scientists used scanning tunneling electron microscope method to directly observe the DNA double helix DNA double helix: in 1952, Austria-American biochemists Chargaff (E.chargaff, 1905 -) of the DNA base pairs in the four kinds of Content found gland fat methotrexate and equal to the number of thymine, cytosine bird fat methotrexate and the number of the same. This makes Watson, Crick immediately think of four kinds of bases exists between the corresponding relations between February 2 and formed a gland fat methotrexate and thymine pairs, the birds fat methotrexate cytosine pairs with the concept