1、Nucleotide,Wu XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,Chapter 3,Wu XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,2,Degrees of freedom:,5,3,Wu XZ, PhD Xz_ 54237697,3,Structural Variation Defined by Bases,normal,frequent,never,Never (except in intercalation),Common,Comm

2、on,Wu XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,4,Propeller Twist,Buckle,Textbook,Real Life,3.6nm,Wu XZ, PhD Xz_ 54237697,5,Pyrimidine-Purine Steps Have Little Base Stacking,Wu XZ, PhD Xz_ 54237697,6,Purine-Pyrimidine Steps Have Extensive Base Stacking,Wu XZ, PhD Xz_ 54237697,7,Doub

3、le helix A,low humidity,More compact,RNA-DNA RNA-RNA,11 base /turn tilted,75%,Left-handed,zigzag,Pu-Py,In cells,DNA Z,DNA Z,Wu XZ, PhD Xz_ 54237697,8,Wu XZ, PhD Xz_ 54237697,9,Rotation of Glycosidic Bond,N3,A,B DNA,Z DNA (G only),A,Trans,Cis,Wu XZ, PhD Xz_ 54237697,10,A,B,Z,Wu XZ, PhD Xz_ 54237697,1

4、1,Double helices,Wu XZ, PhD Xz_ 54237697,12,(四) Other structures,C and T in one strand and A and G in the other.,A triple-stranded DNA structure,poly(A) and polydeoxy(U) are mixed,can be targeted by short matching poly (C+T).,1. Hoogsteen base pairs,Wu XZ, PhD Xz_ 54237697,13,Hoogsteen base pairs,Wu

5、 XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,14,Wu XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,15,H-DNA natural,(recombination and DNA repair).,Wu XZ, PhD Xz_ 54237697,16,2. Quadruple helixes of DNA,Wu XZ, PhD Xz_ 54237697,17,Parallel telomere quadruple,Wu XZ, PhD Bioch

6、emistry Shanghai Medical College Xz_ 54237697,18,堿基序列依賴性的局部DNA 可形成發(fā)夾形或十字形結(jié)構(gòu),3. Local hair pin or cross structure,Wu XZ, PhD Xz_ 54237697,19,二、 Tertiary structure of DNA,the double strands are intertwined,fold, twist, and turn further,superhelix or supercoil,Wu XZ, PhD Xz_ 54237697,20,Significance,Wu

7、 XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,21,Twist Induces Supercoiling,Wu XZ, PhD Xz_ 54237697,22,(一) topoisomers,1. DNA topoisomer different in,Wu XZ, PhD Xz_ 54237697,23,Positive supercoil,wound around one another more tightly,Twisting in the same sense,Wu XZ, PhD Biochemistry S

8、hanghai Medical College Xz_ 54237697,24,Negative supercoil,Twisting in the opposite sense,less tightly,Wu XZ, PhD Xz_ 54237697,25,(二) Many DNA Molecules Are Circular.,Wu XZ, PhD Xz_ 54237697,26,1. Circular DNA forms a closed structure.,no free ends,cannot unwind freely,Wu XZ, PhD Xz_ 54237697,27,Unw

9、inding and subsequent supercoiling,nucleoids,Wu XZ, PhD Xz_ 54237697,28,2. Twist & Writhe,The twist is the number of helical turns in the DNA,Writhe is global contortions of a DNA molecule.,interconvertible,Wu XZ, PhD Xz_ 54237697,29,Sum of twist and writhe.,Lk = Tw +Wr,Wu XZ, PhD Xz_ 54237697,30,Be

10、lt analog to Supercoiling.,Wu XZ, PhD Xz_ 54237697,31,LK negative supercoiling and/or underwinding LK negative supercoiling /underwinding .,left,right,Lk, the Change of LK,Wu XZ, PhD Xz_ 54237697,32,LK,Only if breaks, will LK change.,an invariant property of DNA,cannot change freely,Wu XZ, PhD Xz_ 5

11、4237697,33,3. Topoisomerase type I,make a transient break in one strand of DNA (&),Release negative supercoils,change linking number +1 per action,Wu XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,34,topoisomerase I no ATP,Wu XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,35,

12、Type II topoisomerases,ATP,Wu XZ, PhD Xz_ 54237697,36,（三）Eukaryotic Nuclear DNA Forms Chromatin.,Wu XZ, PhD Xz_ 54237697,37,Core particles,Linking DNA,Histone core,Wu XZ, PhD Xz_ 54237697,38,Solenoid model of the 30-nm condensed chromatin fiber in a side view. Adapted from M. Grunstein, 1992, Sci. A

13、m. 267:68,Wu XZ, PhD Xz_ 54237697,39,6 nucleosomes /turn,10nm,Solenoid,Chromosome 1400nm 10000 x,300nm fiber, 40 x,700nm fiber,Diameter 30nm 100 x,Wu XZ, PhD Xz_ 54237697,40,（四）telomere,natural end,the terminus of chromosomal DNA + related protein,It seals the end,Wu XZ, PhD Xz_ 54237697,41,Telomere

14、 structure,Wu XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,42,Telomerase,Wu XZ, PhD Xz_ 54237697,43,三、 DNA as the genetic material,Wu XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,44,(一) Bacterial DNA transformation,Wu XZ, PhD Xz_ 54237697,45,(二) genome and gene,Wu XZ, PhD

15、 Biochemistry Shanghai Medical College Xz_ 54237697,46,Size of DNA molecule,Wu XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,47,第三節(jié) Structure and Function of RNA,Wu XZ, PhD Xz_ 54237697,48,(一) eukaryotic mRNA is capped,mRNA is capped,linkage,methyl groups,5 terminus guanine,一、Eukaryotic

16、 mRNA,Wu XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,49,1、Cap sequence,m7GpppNm-,Wu XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,50,Wu XZ, PhD Xz_ 54237697,51,Cap is added after transcription.,5,+,5 5,Wu XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,52,Methy

17、lation,Wu XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,53,Every eukaryotic mRNA is capped.,more than one type ?,Whether mRNA is invariant ?,The proportions.,Wu XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,54,Roles of Cap,protection,translation,Cap binding protein,transpla

18、ntation,Wu XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,55,2、mRNAs have 3 Poly A tail,most mammalian mRNAs,polyadenylated with 20-250 A,Wu XZ, PhD Xz_ 54237697,56,Synthesis of poly A tail,poly(A) polymerase,20-250,enzyme,adding,site,free 3-OH end,Wu XZ, PhD Biochemistry Shanghai Medical College Xz_ 54237697,57,Binding of proteins,One PABP 70 kD in every 10-20 A. a stretch of poly(A) to a large mass of protein.,AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA,Wu XZ, PhD Xz_ 54237697,58,