NatureofNucleicacidsDNA.pptVIP

Some special structures of DNA Inverted repeats 反向重复 IR is functionally important as recognition sites on the DNA for the binding of a variety of proteins (e.g. restriction and modification enzymes) IR is either discontinuous or continuous, i.e. with or without non-IR gaps Continuous ? palindromic structure (回文结构) Discontinuous ? hairpin cruciform (发卡、十字结构) Some special structures of DNA Palindrome (回文)： A palindrome is a word, phrase, or sentence that is spelled identically reading forward or backward 莺啼岸柳弄春晴，柳弄春晴夜月明。 明月夜晴春弄柳，晴春弄柳岸啼莺。 level, rotator, madam Was it a rat I saw? In DNA inverted repetitions of base sequence over the two strands form a symmetric structure ? palindromic structure 5’ 3’ 3’ 5’ Some special structures of DNA self complementary within each of the strands and therefore have the potential to form hairpin or cruciform 发卡结构 十字结构 or “stem and loop” 茎环结构 Some special structures of DNA DNA triplex (DNA 三链体) The intramolecular triplex (H-DNA) as an example AG-rich strand vs. CT-rich strand Mirror inverted repeat a barrier for different DNA and RNA polymerases, and so it is a negative regulator for gene expression. G-quadruplexes G-rich sequence(s) to form 4-stranded structure by unusual G-G H-bonds G-quadruplex can be intramolecular, bimolecular or tetramolecular; also can be parallel or antiparallel. Some special structures of DNA （DNA 四链结构） G G G G M+ G-quadruplexes Often seen in the telomeres (端粒), regulating telomere maintenance; also seen in some active genomic sequences, functional in gene regulation. Some special structures of DNA （DNA 四链结构） 3D Structure of the intramolecular human telomeric G-quadruplex in potassium solution. Three layers of G-tetrads are shown by green and blue. Tertiary Structure of DNA Advanced folding and intertwining of DNA molecules over the secondary structure – superhelix structure This is a famous electron micrograph of an E. coli cell that has been carefully lysed,