生物科技伦理学课件.ppt
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1、後基因體時代的倫理素養陳錦生長榮大學生科系John Naisbittin“Megatrends 2000”你也許不懂生物科技你也許不懂生物科技但你不能不知道它的最新發展但你不能不知道它的最新發展否則你就是縱容別人以上帝自居否則你就是縱容別人以上帝自居基因改造過的生物會不會破壞自然生態基因改造過的生物會不會破壞自然生態將來會不會有人頭馬之類的怪物出現將來會不會有人頭馬之類的怪物出現人類憑什麼干預生命的奧秘過程人類憑什麼干預生命的奧秘過程科學家會不會唯利是圖科學家會不會唯利是圖 濫用科技濫用科技你推卸不了道義責任你推卸不了道義責任19531953年英國劍橋大學博士生詹姆斯華生(年英國劍橋大學博士生
2、詹姆斯華生(James D.James D.WatsonWatson),及法蘭西斯克立克(),及法蘭西斯克立克(Francis Crick Francis Crick)發現)發現的雙螺旋結構,證實了是所有生命的核心的雙螺旋結構,證實了是所有生命的核心A structure for Deoxyribose Nucleic Acid The year 1953 could be said to mark,in biology at least,the end of history.Here is James Watson and Francis Cricks paper on the struct
3、ure of DNA,which ushered in the new era with the celebrated understatement near the end.(as published in NATURE magazine)2 April 1953MOLECULAR STRUCTURE OF NUCLEIC ACIDSA Structure for Deoxyribose Nucleic Acid We wish to suggest a structure for the salt of deoxyribose nucleic acid(D.N.A.).This struc
4、ture has novel features which are of considerable biological interest.A structure for nucleic acid has already been proposed by Pauling and Corey(1).They kindly made their manuscript available to us in advance of publication.Their model consists of three intertwined chains,with the phosphates near t
5、he fibre axis,and the bases on the outside.In our opinion,this structure is unsatisfactory for two reasons:(1)We believe that the material which gives the X-ray diagrams is the salt,not the free acid.Without the acidic hydrogen atoms it is not clear what forces would hold the structure together,espe
6、cially as the negatively charged phosphates near the axis will repel each other.(2)Some of the van der Waals distances appear to be too small.Another three-chain structure has also been suggested by Fraser(in the press).In his model the phosphates are on the outside and the bases on the inside,linke
7、d together by hydrogen bonds.This structure as described is rather ill-defined,and for this reason we shall not comment on it.We wish to put forward a radically different structure for the salt of deoxyribose nucleic acid.This structure has two helical chains each coiled round the same axis(see diag
8、ram).We have made the usual chemical assumptions,namely,that each chain consists of phosphate diester groups joining-D-deoxyribofuranose residues with 3,5 linkages.The two chains(but not their bases)are related by a dyad perpendicular to the fibre axis.Both chains follow right-handed helices,but owi
9、ng to the dyad the sequences of the atoms in the two chains run in opposite directions.Each chain loosely resembles Furbergs2 model No.1;that is,the bases are on the inside of the helix and the phosphates on the outside.The configuration of the sugar and the atoms near it is close to Furbergs standa
10、rd configuration,the sugar being roughly perpendicular to the attached base.There is a residue on each every 3.4 A.in the z-direction.We have assumed an angle of 36 between adjacent residues in the same chain,so that the structure repeats after 10 residues on each chain,that is,after 34 A.The distan
11、ce of a phosphorus atom from the fibre axis is 10 A.As the phosphates are on the outside,cations have easy access to them.The structure is an open one,and its water content is rather high.At lower water contents we would expect the bases to tilt so that the structure could become more compact.The no
12、vel feature of the structure is the manner in which the two chains are held together by the purine and pyrimidine bases.The planes of the bases are perpendicular to the fibre axis.The are joined together in pairs,a single base from the other chain,so that the two lie side by side with identical z-co
13、-ordinates.One of the pair must be a purine and the other a pyrimidine for bonding to occur.The hydrogen bonds are made as follows:purine position 1 to pyrimidine position 1;purine position 6 to pyrimidine position 6.If it is assumed that the bases only occur in the structure in the most plausible t
14、automeric forms(that is,with the keto rather than the enol configurations)it is found that only specific pairs of bases can bond together.These pairs are:adenine(purine)with thymine(pyrimidine),and guanine(purine)with cytosine(pyrimidine).In other words,if an adenine forms one member of a pair,on ei
15、ther chain,then on these assumptions the other member must be thymine;similarly for guanine and cytosine.The sequence of bases on a single chain does not appear to be restricted in any way.However,if only specific pairs of bases can be formed,it follows that if the sequence of bases on one chain is
16、given,then the sequence on the other chain is automatically determined.It has been found experimentally(3,4)that the ratio of the amounts of adenine to thymine,and the ration of guanine to cytosine,are always bery close to unity for deoxyribose nucleic acid.It is probably impossible to build this st
17、ructure with a ribose sugar in place of the deoxyribose,as the extra oxygen atom would make too close a van der Waals contact.The previously published X-ray data(5,6)on deoxyribose nucleic acid are insufficient for a rigorous test of our structure.So far as we can tell,it is roughly compatible with
18、the experimental data,but it must be regarded as unproved until it has been checked against more exact results.Some of these are given in the following communications.We were not aware of the details of the results presented there when we devised our structure,which rests mainly though not entirely
19、on published experimental data and stereochemical arguments.It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.Full details of the structure,including the conditions assumed in building it,together wit
20、h a set of co-ordinates for the atoms,will be published elsewhere.We are much indebted to Dr.Jerry Donohue for constant advice and criticism,especially on interatomic distances.We have also been stimulated by a knowledge of the general nature of the unpublished experimental results and ideas of Dr.M
21、.H.F.Wilkins,Dr.R.E.Franklin and their co-workers at Kings College,London.One of us(J.D.W.)has been aided by a fellowship from the National Foundation for Infantile Paralysis.J.D.WATSON F.H.C.CRICK Medical Research Council Unit for the Study of Molecular Structure of Biological Systems,Cavendish Lab
22、oratory,Cambridge.April 2.1.Pauling,L.,and Corey,R.B.,Nature,171,346(1953);Proc.U.S.Nat.Acad.Sci.,39,84(1953).2.Furberg,S.,Acta Chem.Scand.,6,634(1952).3.Chargaff,E.,for references see Zamenhof,S.,Brawerman,G.,and Chargaff,E.,Biochim.et Biophys.Acta,9,402(1952).4.Wyatt,G.R.,J.Gen.Physiol.,36,201(195
23、2).5.Astbury,W.T.,Symp.Soc.Exp.Biol.1,Nucleic Acid,66(Camb.Univ.Press,1947).6.Wilkins,M.H.F.,and Randall,J.T.,Biochim.et Biophys.Acta,10,192(1953).VOL 171,page737,1953生物技術的世紀1980年,第一個人工改造的細菌獲得專利1977年,桃麗羊複製成功2000年,人體基因組解碼獲初步成功基因工程技術的蓬勃發展複製人?生物科技倫理議題胚胎地位的爭議基因改造食品人體基因計畫複製技術帶來的社會衝擊生殖科技幹細胞基因行為學動物權基因專利及商業
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