核酸化学

1. 核酸化学 Nucleic Acid Chemistry

2. contents 1 introduction 2 compositiong 3 Structure 4 nucleic acid and nucleotide property

3. ⅠIntroduction 1.discovery and developmentof nucleic acid • 1868, Fridrich Miescher first isolated nuclein from pyocyte(脓细胞）.

4. 1944 O.Avery confirmed DNA is hereditary substance.

5. Rosalind Franklin and Maurice Wilkins showed in the early 1950s that DNA produces a characteristic x-ray diffraction pattern 1953 J.Watson F.Crick discovered DNA double helix.

6. 1968, Nirenberg found the genetic code . Marshall W. Nirenberg

7. 2. classification,distributing and function of nucleic acids

8. Ⅱcomposition of nucleic acid

9. Nucleic Acids Nucleotide phosphate Ribonucleoside(deoxyribonucleoside) base Pentose deoxyribose ribose Purine (A、G) Pyrimidine (C、T、U)

10. Nucleotide

11. pentose

12. Base

13. 7 6 1 3 8 7 1 1 6 8 9 2 3 3 1

14. Ribonucleoside cytidine胞苷CR guanine deoxyriboside 脱氧鸟苷dGR

15. The linkage of base with ribose(2-deoxyribose)

16. Deoxyribonucleotides The product of deoxyribonucleoside linking of phosphoric acid at 5’ position.

17. ribonucleotides

18. Important nucleotides

20. minor bases

21. I Ψ

22. Ⅲ structure of nucleic acid 1、 structure of DNA (1) The primary structure The primary structure of a nucleic acid is its covalent structure and nucleotide sequence.

23. The primary structure DNA was formed by linking of deoxynucleotides with phosphodiester bond at 3’ position of one deoxynucleotide and 5’ position of another deoxynucleotide.

25. (2) Secondary structure – Double-stranded helix • Characteristic • The two strands are antiparallel. • The chain, phosphoric acid and deoxyribose, locate lateral of the helix, but bases are in the helix. • Pair strictly A to T, G to C. • A turn contains 10 nucleotides, with height 3.4nm. Width 2.0nm. • Form a major groove and a minor groove. • Rotating right-handed. • The maintaining force of the structure is hydrogen-bond.

26. Pairs bases

27. 2.0 nm 小沟 大沟 The Nobel Prize in Physiology or Medicine 1962 (1953) Watson and Crick

28. Versatility of DNA double helix A-DNA is favored when DNA is dehydrated. Major and minor grooves are similar in width. B-DNA is the conformation normally found inside cells. Z-DNA is favored in certain G/C-rich sequences. No grooves left handed helix

29. Versatility of DNA double helix

30. forces two sets of forces, as described earlier: 1. hydrogen bonding between complementary base pairs 2. base-stacking interactions.

31. (3) Tertiary structure of DNA----supercoil Further coil of the DNA double helix. (positive supercoil) (negative supercoil)

32. (4) Function of DNA (1) Containing genetic information, as the template of gene duplication , DNA finally directs protein biosynthesis. As a result, keeping hereditary characters of body. (2) Gene refer to a segment of DNA chain which posseses a special biological function.

33. 2. spatial structure and function of RNA RNAs in animal cell

34. (1) mRNA --messenger RNA • 5’cap:m7GpppNm- • 3’Poly A tail：An n=20—200 • Single chain • half life time from munits to hours

36. In prokaryotes a single mRNA molecule may code for one or several polypeptide chains. If it carries the code for only one polypeptide, the mRNA is monocistronic; if it codes for two or more different polypeptides, the mRNA is polycistronic. In eukaryotes, most mRNAs are monocistronic. mRNAs transcribed from DNA are always somewhat longer than needed simply to specify the code for the polypeptide sequence(s). The additional noncoding RNA includes sequences that regulate protein synthesis .

37. (2) tRNA --transfer RNA Secondary structure ★ Stem-loop structure, cloverleaf pattern三叶草形. ★3 loop and 1 arm: DHU loop, anticoden loop, Tφloop, AA arm. ★Anticoden and CCA-OH 3’end. ★Contain rare bases 10%-20%.

38. tRNA tertiary structure: a inverse L like.

39. tRNA functions as a amino acid transfer in protein biosynthesis.

41. (3) rRNA --ribosomal RNA • Weight 80% of total RNA in a cell. • Flower like. • Component of ribosome. • procaryote：5S,16S,23S; • eukaryote: 18S,5S,5.8S,28S

43. Ⅳ nucleic acid and nucleotide property

44. 1. Ultraviolet absorption • Nucleic acids get their maximum absorption at 260nm. • DNA solution：A260／A280=1.8; RNA solution：A260／A280= 2.0 • OD260=1.0, equal to 50μg/ml DS DNA, 40μg/ml SS DNA or RNA.

45. hyperchromic effect • The large increase in light absorption at 260 nm occurring as a double-helical DNA is melted (unwound). • hypochromic effect • The close interaction between stacked bases in a nucleic acid has the effect of decreasing the absorption of UV light relative to a solution with the same concentration of free nucleotides. This is called the hypochromic effect.

46. 2. DNA denaturation --the double chain change into single chain Methods: heat, acid, base, urea, acetone Result: OD260↑, viscosity↓, activity lose.

47. Tm --melting temperature, 解开链温度，融解温度，refer tothe middle point of temperature range of DNA thermal denaturation . • The temperature of 50% double chain undoing. • Tm=69.3+0.41(G+C)%

49. Renaturation and hybridization Renaturation: the single DNA chains recover their natural double helix structure. Annealing退火: renaturation of thermal denatural DNA, by way of slow cooling.

50. Hybridization杂交：phenomenon of single chain DNA or RNA bind the chain different origin in renaturation process.