11.09.2008

The structure of dna

DNA is composed of many DNA residue, according to a certain order each other with 3 ', 5'-phosphate ester linked to the composition of long chain. DNA contains a majority of two such long-chain, and some for single-stranded DNA, such as E. coli phage φX174, G4, M13 and so on. Some DNA for the ring, and some for the linear DNA. Contains adenine, guanine, thymine and cytosine base 4. In some types of DNA, 5 - cytosine methylation may to a certain extent replaced by cytosine, wheat germ DNA of the 5 - cytosine-rich in particular, up to 6% of the mole. In some phage, 5 - hydroxymethyl cytosine replaced cytosine. In the late 40, Gabriel Richard (E. Chargaff) found that different species of the base composition of DNA, but the number of adenine equal to the number of its thymine (A = T), guanine cytosine number equal to the number (G = C), and therefore the number of purine and pyrimidine equal to the number of and. Several described by the general level of the structure of DNA.
A structure of the primary structure of DNA that is its base sequence. Gene is a fragment of DNA, genetic information stored in its base sequence. In 1975 the United States Gilbert (W. Gilbert) and the United Kingdom's Sanger (F. Sanger) respectively, created the structure of the DNA level, the rapid determination of their total end of 1980 Nobel Prize in Chemistry. Since then, the method also has been improved, many of the primary structure of DNA has been established. If people ring of mitochondrial DNA contains 16,569 base pairs, λ phage DNA contains 48,502 base pairs, rice chloroplast genome contains 134,525 base pairs, tobacco chloroplast genome contains 155,844 base pairs, and so on. Now the United States has plans to 10-15 years in all human DNA molecule of about 3,000,000,000 for the nucleotide sequence out.
Secondary structure in 1953, Watson (Watson) and Crick (Crick) put forward the basic structure of DNA fiber is a double helix structure, then this model has been recognized scientists, and to explain to copy, transcription, and other important life processes. After an in-depth study and found that humidity and as a result of base sequences in different conditions, DNA double helix can have a variety of types, mainly divided into A, B and Z three categories.
It is generally believed, B cells closest to the structure of DNA conformation, it is very similar to the double helix model. A-DNA and RNA molecules in the two-time transcription, as well as the district Screw the formation of the DNA-RNA hybridization close to the molecular conformation. Z-DNA nucleotide dimer to the left to the wound as a unit, which was the main chain saw (Z)-shaped, and named. This configuration for multi-purine nucleotide chains of alternating pyrimidine area. In 1989, U.S. scientists used scanning tunneling electron microscope to directly observe the double helix DNA double helix DNA ︰ 1952, Austria-American biochemist Chargaff (E.chargaff, 1905 -) was determined by DNA base pairs in the 4 Content and found that methotrexate gland and fat equal to the number of thymine, cytosine and methotrexate fat birds of the same number. This Watson, Crick immediately think of base 4 between 22 corresponds to the relationship between the formation of the gland fat and thymine pair methotrexate, methotrexate fat birds and the concept of cytosine pair.
High structure
Triplex DNA (T-DNA)
In the early 1950s, Wilkins According to the X-ray diffraction pictures have been envisaged in the DNA chain may be 3, Crick later watson and others have to build some T-DNA model. Has found that the three DNA chain can be divided into two categories, namely, three helix structure of the Chinese Academy of Sciences and in 1990 by Bai Chunli, such as scanning tunneling electron microscope techniques to observe the structure of the three Fabian "
Three in the spiral structure of DNA double helix structure formed on the basis of the three chains District 3 chain are homologous or homologous pyrimidine purine that the entire base of the pyrimidine purine or, in accordance with section 3 of the chain of sources , The DNA chain can be divided into three elements and between elements within the two groups, according to the 3 components of the chain as well as the relative positions can be divided into Pu-Pu-Py and Py-Pu-Py-two (Pu-generation
Table purine chain, Py pyrimidine on behalf of the chain) is one of the most common Py-Pu-Py type, it's 3 in the chain there are 2 for a normal double helix, 3 pyrimidine chain located in the double helix of the big ditch, Purine with the chain in the same direction and with the double helix structure of the rotation together, the three chains in the base pairs of DNA double helix with the same, that is, their base is still AT, GC matching However, No. 3 chain C must be protonated , And G with only 2 to form hydrogen bonds (normally three hydrogen bonds).
Triplex DNA research will help shed further light on the structure of chromosomes and genes in eukaryotic transcription, replication, and re-regulation and control mechanism. In addition three DNA chain have a certain value, such as the availability of single-stranded DNA fragments will be cutting agent (such as the endonuclease) to carry DNA to a specific site, so as to achieve selective chromosome DNA hit off the end, because the cells Transcription factors such as regulation and protein only after the combination of DNA double helix to open its specific gene transcription, transcription factors can not helical and the three combined, it can make use of oligo DNA fragment closure of the transcription factor binding sites in order to reach the turn off harmful genes or Virus genes.
Quadruplex DNA
Klug and Sundpuist in a simulated 1 kind of spike protozoan telomere DNA of the caterpillar, paragraph 1 of the synthetic DNA sequences and found that under certain conditions, the simulation of G-rich single-stranded DNA to form a quadruplex DNA structure. This chromosome that the end of the telomere single strand between the formation of a four-chain. Kang and others were confirmed by experiments in crystal and in solution, the rich G DNA can form a quadruplex DNA structure.
Quadruplex DNA is the basic structure of the G-quadruplex, that is, in the four conjoined at the center there are 4 by a negative charge with the carboxylic oxygen atoms surrounded the "pocket" through the G-quadruplex accumulation can be Elements to form molecules or between right-handed spiral, with the double helix structure of DNA comparison, G-quadruplex spiral 2 significant characteristics: 1, the stability of its decision in the pocket by the combination of cation type, known ion k The combination of quadruple-helix so that the most stable; 2, and its thermodynamic stability of the very nature and dynamics.
At present some of the biological DNA sequence analysis that the G-rich DNA sequence found in some of the functions and evolution are very conservative region of the genome, many studies have shown that guanine-rich DNA chain formed by G-DNA may be As the mutual recognition between the molecular components of one of the organisms in the cell plays a special role