ppt模板紫色地球信息主題(存儲版)
【正文】 of a simple TTAGGG sequence.[46] ? DNA quadruplex formed by telomere repeats. The looped conformation of the DNA backbone is very different from the typical DNA helix.[47] ? These guaninerich sequences may stabilize chromosome ends by forming structures of stacked sets of fourbase units, rather than the usual base pairs found in other DNA molecules. Here, four guanine bases form a flat plate and these flat fourbase units then stack on top of each other, to form a stable Gquadruplex structure.[48] These structures are stabilized by hydrogen bonding between the edges of the bases and chelation of a metal ion in the centre of each fourbase unit.[49] Other structures can also be formed, with the central set of four bases ing from either a single strand folded around the bases, or several different parallel strands, each contributing one base to the central structure. 樣例文本 B ? At the ends of the linear chromosomes are specialized regions of DNA called telomeres. The main function of these regions is to allow the cell to replicate chromosome ends using the enzyme telomerase, as the enzymes that normally replicate D
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