In many kindspolymerDue to the interaction between the side groups of adjacent molecular chains and the requirements of the closest stacking, the molecular chains in the crystal region of the crystal region of the crystal region of the crystal region adopt the conformational arrangement of trans and left-right forms in different alternate ways, forming a spiral structure.
EveryscrewThe number of monomer units included in the identity cycle varies with the size of substituents and the interaction.Generally, p/g is used to represent the form of spiral structure, which means thatIdentical periodThere are pMonomer unit, spiral q ring.asIdentical polystyrene crystal areaThe molecular chain of is 3/1 (TG)Helical conformation, in thisstructureThe middle trans form and the left and right form are arranged alternately.SyndiotacticpolystyreneIt is possible to form a 4/1 (TTGG) spiral conformation, that is, two trans forms and two left-right forms are alternately arranged.
Quadruplex helical structure
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stayJames Watson andFrancis Crick Established DNA asDouble helix structureAfter 60 years of this theory, a kind of four strand helical DNA appeared.Four strand helical structure formed by four rather than two DNA strands[1], has been found in the laboratory and human cancer cells.This four stranded DNA spiral structure, called G-quadruplex, is formed by the interaction of four bases.These four bases form aSquare structure。They seem to be a temporary structure, and they are the most numerous when cells are ready to divide.They appear in the center of the chromosome and in the telomere region.Telomeres are DNA sequences that protect chromosomes from damage at the ends of chromosomes.This discovery can challenge the traditional belief that we really understand the structure of DNA because Watson and Crick discovered the double helix structure in 1953.
Using an antibody material that only binds to G-quadruplex, scientists found the above-mentioned quadruplex helix structure in cancer cells.In order to prevent the quadruplex spiral structure from disintegrating into a common DNA structure, researchers try to lock the quadruplex spiral in its formation position.This allows researchers to calculate how many quadruplex helical structures are formed in each step of cell replication.The number of G-quadruplexes is the largest at the S stage, the stage of DNA replication before cell division.This research further highlights the potential of using these unusual DNA structures to treat cancer.Another important question that scientists will try to answer is whether G-quadruplex willembryonic developmentAnd whether this effect is wrongly reactivated in cancer cells;The plan is to find out whether the four strand spiral structure is a natural damage or an intentional act.
Helical structure
By folding a synthetic DNA strand containing a large number of guanine bases, a square DNA structure very different from the double helix structure can be obtained in the laboratory.A G-quadruplex consists of four guanine bases located at different positions of the DNA chain rich in guanine bases, which are bound together by a special type of hydrogen bond to form a breakDNA double helix structureCompact square structure.G-quadruplexes do form in cells and these unusual structures may have important biological functions.
