1、分子生物学分子生物学1 -分子生物学的发展分子生物学的发展 生物学的昨天、今天和明天 生物学的定义：生物学的定义：一门关于生命的科学一门关于生命的科学 生物学家需要在许多层次进行他们的研究生物学家需要在许多层次进行他们的研究 原子原子分子分子细胞细胞组组织织器官器官有机体有机体群落群落 生物学的昨天、今天和明天 人是一架机器吗？人是一架机器吗？中世纪中世纪 机械论者与活力论者的持久争执机械论者与活力论者的持久争执 1628年威廉年威廉.哈维发现血液循环哈维发现血液循环 1828年弗里德里希年弗里德里希.味勒在实验室合成了尿素味勒在实验室合成了尿素生物学的昨天、今天和明天 现代生物学的开端现代生
2、物学的开端：显微镜显微镜细胞细胞 电子显微镜电子显微镜 X-ray晶体衍射晶体衍射分子分子 分子生物学的涵义分子生物学的涵义分子生物学（分子生物学（Molecular Biology)顾名思义：在分子水平上研究生命过程的科学。分子生物学研究是在分子水平上研究基因和基因的活动，是对遗传学内容的新理解，更贴切的术语是分子遗传学分子遗传学。研究的主要内容：研究的主要内容：Three Major ApproachesStructural(architecture of the molecules)Biochemical(interactions between cell metabolism and
3、heredity)Informational(transfer of information,translation of information)分子生物学不是单一界分子生物学不是单一界限分明的学科限分明的学科 Dr.F.Crick 谈到自己的研究领域时：“我勉强称自己为分子生物学家，因为爱打听的牧师问我做什么工作时，我已经为解释自己兼为结晶学家、生物物理学家、生物化学家和遗传学家而感到厌烦”Mendel:The Father of Genetics Made brilliant insights into heredity.Began classical experiments into
4、heredity involving pea plants beginning in 1854.Established Principle of Segregation as well as the concept of dominant and recessive traits.Questions surround Mendels findings Mendels ideas seem obvious today.This was not the case in the past.No one had ever heard of a“gene”in Mendels time.Biologis
5、ts previously failed to distinguish between heredity and development.发现发现 DNA Friedrich Miescher(Swiss,1844-1895)Intelligent from early age but very shy His father was a professor of anatomy Studied at the University of Gttingen under Ernst Felix Immanuel Hoppe-Seyler,considered the father of bioche
6、mistry He examined used bandages obtained from a hospital caring for the wounded of the Crimean War in hope of finding something interesting He discovered a substance containing both phosphorus and nitrogen,made up of molecules that were apparently very large,in the nuclei of white blood cells found
7、 in pus Named the substance nuclein（核素）核素）because it seemed to come from cell nuclei.In 1874 when Miescher separated it into a protein and an acid molecule.It is now known as deoxyribonucleic acid(DNA)This substance was so unusual that Hoppe-Seyler repeated the work himself before allowing Miescher
8、to publish the paper on the discovery He found an excellent(and more pleasant)source of nuclear material in the sperm of the salmon The nuclei are large in any sperm cells,remarkably so in the salmons From these he first extracted a pure DNA In 1889 a pupil of his,the German pathologist Richard Altm
9、ann(1852-1900)introduced the term “nucleic acid”先天性代谢障碍先天性代谢障碍 Archibald Garrod(British,1857-1936)His father was a physician Received his medical training at St.Bartholomews Hospital,London The relationship between genes and proteins was first proposed by Garrod in 1908 Garrod,a prominent physician
10、at St.Bartholomews Hospital in London,understood both the new science of biochemistry and the emerging discipline of genetics He studied a harmless but rare disorder in the general population but frequent in children of first-cousin marriages:alkaptonuria（尿黑酸尿症）尿黑酸尿症）A patient with this disorder pro
11、duces urine that when exposed to air turns distinctively dark,because these people lack the enzyme found in normal individuals who are able to convert the reddening agent,alkapton（尿黑酸）尿黑酸）,to another substance Following Mendels laws,Garrod concluded that alkaptonuria is a congenital disorder,not the
12、 result of a bacterial infection as was commonly thought He observed that inherited diseases reflect a patients inability to make a particular enzyme,which he referred to as“inborn errors of metabolism”Garrods hypothesis was ahead of its time In the 1930s George Beadle and Boris Ephrussi linked the
13、synthesis of pigments to eye color in fruit flies to specific mutations1910-1925:细胞遗传学的进展细胞遗传学的进展 Cytogenetics is the study of chromosomes and chromosome abnormalitiesX-ray衍射晶体分析法衍射晶体分析法 X-ray crystallography is a technique that exploits the fact that X-rays are diffracted by crystals It is not an i
14、maging technique:X-rays have the proper wavelength to be scattered by the electron cloud of an atom of comparable size Based on the diffraction pattern obtained from X-ray scattering off the periodic assembly of molecules or atoms in the crystal,the electron density can be reconstructed In 1912 Max
15、von Laue reported the diffraction of X rays by a crystal(for which he received a Nobel Prize in physics in 1914)For progress in pharmaceutical research the structure of complex organic molecules has to be understood By studying the chemical reactions that a compound and its degradation products coul
16、d enter into with other compounds of known structure,chemists were able to deduce the structures of many complex organic molecules X-ray crystallography allowed to determine molecular structure from the compound itself.In this method,structural information is obtained by mathematical analysis of the
17、 intensity of X rays scattered(or diffracted)from parallel planes in a crystal,as recorded photographically or by an electronic detector In 1915 a unique father-son team,William Henry Bragg(18621942)and his son,William Lawrence Bragg(18901971),won the Nobel Prize in physics for their seminal roles i
18、n X-ray crystallographyWilliam Lawrence Bragg(left)and William Henry Bragg William Henrys original interest was in what diffraction showed about the nature of X-rays,and he was a skilled experimenter and designer of instruments William Lawrence was more concerned with what X-rays revealed about the
19、crystalline state,and he possessed a powerful ability to conceptualize physical problems and express them mathematically Until electronic computers were developed during World War II,these calculations were incredibly laborious“Transforming Principle”In 1928,Frederick Griffith(British,conducted an e
20、xperiment that showed the transformation of living cells by a“transforming principle”,which was later discovered to be DNA 四核苷酸假说四核苷酸假说 Phoebus Levene(Russian-American,1869-1940)He worked with Albrecht Kossel and Emil Fischer,the nucleic acid and protein experts at the turn of the 20th.century He co
21、nducted experiments that in 1931 suggested that the four components of DNA occur in approximately equal ratios He suggested the possibly that DNA was made of a repeating tetramer If so,the implication was that the structure of DNA was too simple and too regular to contribute to genetic variation:att
22、ention thereafter focused on protein as the probable hereditary substance“一个基因一个酶一个基因一个酶”假说假说 This proposal of the one gene-one enzyme hypothesis was developed by the Americans George Beadle(1903-1989)and George Wells Tatum(1909-1975)in 1938 Beadle and Tatum hypothesized that if there really was a o
23、ne-to-one relationship between genes and specific enzymes,it should be possible to create genetic mutants that are unable to carry out specific enzymatic reactions They exposed spores of Neurospora crassa(a bread mold，一种面包霉菌一种面包霉菌)to X-rays or UV radiation and studied the resulting mutations The mut
24、ant molds had a variety of special nutritional needs.Unlike their normal counterparts,they could not live without the addition of particular vitamins or amino acids to their food Normal Neurospora requires only one vitamin(biotin),but mutants were created that also required thiamine or choline Genet
25、ic analysis showed that each mutant differed from the original,normal type by only one gene Biochemical studies showed that the mutants seemed to be blocked at certain steps in the normal metabolic pathways Their cells contained large accumulations of the substance synthesized just prior to the bloc
26、kage point,just as Garrods patients had accumulated alkapton As Beadle and Tatum had predicted,they created single gene mutations that incapacitated specific enzymes,so that the molds with these mutations required an external supply of the substance that the enzyme normally produced,and the substanc
27、e that the enzyme normally used,piled up in the cell These results confirmed their one gene-one enzyme hypothesis They received the 1958 Nobel Prize in Physiology and Medicine“Transforming Principle”identified as DNA In the early 1940s Oswald T.Avery and Maclyn McCarty,a colleague at the Rockefeller
28、 Institute Hospital,began concentrating on the problem of pneumococcal transformation Averys work focused first on purifying the transforming substance.Using refined versions of Colin M.MacLeods preparation techniques,Avery and McCarty isolated biologically active“transforming principle”from samples
29、 of pneumococci Then attention turned to its chemical analysis.Proteases(enzymes that deactivate proteins)and lipases(enzymes which destroy lipids)were found not to inactivate the transforming principle Avery concluded that the substance was essentially protein and lipid free.He found that the subst
30、ance was rich in nucleic acids,but ribonuclease,an enzyme that destroys ribonucleic acid(RNA),did not inactivate the substance either It was not a carbohydrate like the polysaccharide capsular material,as carbohydrates are not precipitated by alcohol(the“transforming principle”was)Alcohol was,howeve
31、r,a well-known precipitant for deoxyribonucleic acid(DNA).Further,the transforming substance had a high molecular weight,as did DNA,and gave a strong reaction to the Dische test for DNA.Thus,the transforming substance,producing permanent,heritable change in an organism,was DNAWhat is Life?By the end
32、 of WWII,many physicists,saddened by the prospects of atomic bombs,turned their attention toward biology One of them was Erwin Schrdinger(Austrian 1887-1961)Schrdinger published in 1945 a book titled What is Life?that planted the idea for searching“the secret of life”This marked the beginning of red
33、uctionism in biologyBase Ratios In 1951 Edwin Chagraff(1905-2002)noted“regularities”in the base composition of nucleic acids,which reflected the existence in all DNA preparations of certain structural principles In particular,for duplex DNA he identified the constant proportion of bases:%A=%T and%C=
34、%G X-ray Crystallography Applied to Nucleic Acids Between 1940s and 1950s:Maurice Wilkins(1916-)and Rosalind Franklin(1920-1958)worked on X-ray/DNAThe Hershey-Chase Experiment The Americans Alfred Hershey(1908-1997)and Martha Chase(1930-2003)published in 1952 a now classical paper They showed DNA to
35、 be the carrier of genetic information in virus reproduction,working with T2 phage They demonstrated by labeling the capsid proteins and nucleic acid of bacteriophage T2 with different radioactive isotopes that only the DNA of the phage had to enter the cell for virus replication to occurEnter Watso
36、n and Crick James Watson(American,1928-)Francis Crick(British,1916-2004)PrincipleDataSourceX-ray crystallographyStacked layers of subunits in spirals;long chain,no ruling out of two chains,sugar-phosphate in the outsideWilkins and Franklin(but mostly Franklin)Organic chemistry4 nucleotidesLeveneBioc
37、hemistry-helix,model buildingPaulingChromatographyBase ratiosChargaffChemical bondingRight form of the basesJ.DonahueMathematicsAttractive forces between DNA basesJ.GriffithWhat did Watson and Crick Really Contribute?Major original breaks by W&C were the A-T and C-G having the same molecular shape T
38、hat lead to understanding constancy for the diameter of the DNA molecule,the use of Chargaffs ratios The application of model building which lead to the complementary model狂热的追求科学发现之我见 F.Crick“.双螺旋确实是一种了不起的分子，也是一个了不起的发现。现代人的历史约有5万年，文明的 历史几乎不到1万年，美国的历史仅仅200多年，可是RNA、DNA都至少存在了几十亿年。从古至今，双螺旋就一直存在并活跃着，可是我
39、们还是近些年才知道。当然，值得庆幸的是，我们是地球上最先意识到它的存在的生物。有关我们发现双螺旋的文章如此之多，我很难再补充什么。我想说，DNA是由4个字母的语言写成的长长的生命信息，这是生命的语言”美国科学家道金斯道金斯：生命在本质上应该被视作是基因的载体。生命照管自己的基因，并且通过某种特定的方式与同类的基因（通常是这样）相混合，将它们传递给后代以延续种族。生命传递给每一个后代的便是由生命密码组成的启动程序，是基因的特定组合。事实上，当地球生命开始出现的时候，基因的传递便开始了，而且还要永远传递下去，因此，每个生命只是一个暂时的基因载体。果如道金斯所言，生命所经历的实在是一场精致的“悲剧人生”，而生命存在的价值至说人类存在的价值只是携带着一个生命密码箱在生命演进的大道上放足狂奔。History of Genome Project the summit2001 HGP consortium publishes its working draft in Nature(15 Feb):and Celera publishes its draft in Science(16 Feb).
