Genel Biyografiler ve Bilim Adamları Forumunda Roger W. Sperry hayatı Konusunu Okuyorsunuz..
sperry nin hayatı
01 Ekim 2011 11:30
Roger W. Sperry hayatı
Roger W. Sperry yaşamı hakkında genel bilgi
My adult scientific career began with graduate study in chemical physics with Harden McConnell at Stanford. I had the idea of elucidating the mechanism of ion transport across biological membranes by nuclear resonance. I thought ion transport must involve rotation of the transport protein in the membrane. Struggling to prove this wrong idea, it occurred to me to study the rotation in the membrane of a lipid molecule, about 1,000 molecular weight, rather than a protein fifty times larger. This led to my discoveries, by nuclear and paramagnetic resonance methods, of phospholipid flip-flop, an exceedingly slow process, and lateral diffusion, exceedingly fast (Kornberg and McConnell, 1971a ; Kornberg and McConnell, 1971b).
For postdoctoral work, I wanted to learn about the other important method of physico-chemical analysis of macromolecules, X-ray diffraction. The obvious choice was the Laboratory of Molecular Biology (LMB) in Cambridge, where protein crystallography was developed and still most intensively practiced at the time. I went in the spring of 1972 to work with Aaron Klug, who was not only a leading crystallographer, but also responsible for the application of Fourier methods to electron microscopy and image processing. While looking for a problem to study by X-ray diffraction, I got to know Mark Bretscher, the only person at the LMB interested in membrane structure, and he suggested reading a paper just published by Francis Crick titled "A General Model for Higher Organism Chromosomes" (Crick, 1971). Figure 3 of that paper was a diagram showing a loop of DNA crossed by a dashed line, said to symbolize a histone molecule. When I raised the subject with Aaron Klug, he immediately produced a sheaf of papers on the X-ray analysis of chromosomal material, or "chromatin," known for nearly a century to contain roughly equal weights of histones and DNA. Aaron had discussed the interpretation of the X-ray pattern of chromatin extensively with Francis, and he encouraged me to pursue the problem. He warned me, however, that it was a "messy" problem.
Notorious might have been a better word. Many had succumbed to the allure of the problem, with its potential for insight into genetic chemistry, only to be frustrated by the intractability of the histones. These proteins were, on the one hand, surprisingly simple, and on the other hand, hopelessly complicated. There are only five types of histone, designated H1, H2A, H2B, H3, and H4. Upon isolation, however, the individual histones proved to be extraordinarily sticky, binding avidly to DNA and interacting with one another in every possible combination. Whereas the X-ray diffraction pattern of chromatin was indicative of repeating order, the biochemical behavior of the histones did not appear to explain it. There was, moreover, sufficient variation in the relative amounts of the histone types in various tissues and organisms "to make the idea of a unique repeating order untenable" (Huberman, 1973). The histones came to be regarded as a kind of amorphous glue, coating the chromosomal DNA, with no obvious significance.
I began by repeating the work of others, isolating the individual histones, mixing them in various combinations with DNA, and recording X-ray diffraction patterns. I also scoured the literature and came across two papers that influenced my thinking. A paper by Hewish and Burgoyne reported the cleavage of about 10% of chromosomal DNA by an endogenous nuclease in isolated rat liver nuclei to multiples of a unit size (Hewish and Burgoyne, 1973). When I mentioned this to Francis Crick, he shot off a letter to Hewish inquiring about the size. The reply came from Burgoyne, giving the sedimentation coefficient of the unit length of DNA. Assuming the measurement was made under alkaline conditions, as was customary for sedimentation analysis of RNA, much studied at the LMB at the time, the value from Burgoyne corresponded to about 500 bases. This unit size did not relate to any other information about chromatin, and the appearance of multiples of the unit size simply confirmed what we already knew from X-ray diffraction, that chromatin contained some amount of repeating substructure.
The second paper, by van der Westhuyzen and von Holt, reported the extraction of histones from chromatin by mild methods, rather than with strong acid or other harsh treatment, as was customary at the time (van der Westhuyzen and von Holt, 1971). Mild methods failed to resolve the histones entirely from one another, so the paper was ignored. What attracted my attention was the clean separation of the mildly extracted histones into two groups, H2A/H2B, and H3/H4. This separation contrasted with the promiscuous interactions of the histones previously observed. I realized this promiscuity was likely attributable to the denaturation of histones during isolation in the past. From the data in the paper, I could also deduce that the H3/H4 group behaved as if twice the size of the H2A/H2B group, although all four individual histone proteins were about the same size. I concluded that H3 and H4 must form a dimer, and I thought I might crystallize and solve the structure of this unique histone oligomer.
What followed was truly astounding. I measured the molecular weight of the purified H3/H4 preparation by equilibrium ultracentrifugation, while Jean Thomas offered to analyze the material by chemical cross-linking. Both methods showed unequivocally that H3 and H4 were in the form of a double dimer, an (H3)2(H4)2 tetramer (Kornberg and Thomas, 1974). I pondered this result for days, and came to the following conclusions (Kornberg, 1974). First, the exact equivalence of H3 and H4 in the tetramer implied that the differences in relative amounts of the histones from various sources measured in the past must be due to experimental error. This and the stoichiometry of the tetramer implied a unit of structure in chromatin based on two each of the four histones, or an (H2A)2(H2B)2(H3)2(H4)2 octamer. Second, since chromatin from all sources contains roughly one of each histone for every 100 bp of DNA, a histone octamer would be associated with 200 bp of DNA. Finally, the (H3)2(H4)2 tetramer was reminiscent of hemoglobin, an a2b2 tetramer. The X-ray structures of hemoglobin and other oligomeric proteins available at the time were compact, with no holes through which a molecule the size of DNA might pass. Rather, the DNA in chromatin must be wrapped on the outside of the histone octamer.
As I turned these ideas over in mind, it struck me how I might explain the results of Hewish and Burgoyne. What if their sedimentation coefficient of unit length DNA fragments was measured under neutral rather than alkaline conditions? Then the DNA would have been double stranded and about 250 bp in length. Allowing for the approximate nature of the result, the correspondence with my prediction of 200 bp was electrifying. Then I recalled a reference near the end of the Hewish and Burgoyne paper to a report of a similar pattern of DNA fragments by Williamson. I rushed to the library and found that Williamson had obtained a ladder of DNA fragments from the cytoplasm of necrotic cells and measured the unit size by sedimentation under neutral conditions: the result was 205 bp! I was euphoric. In the months and years to follow, it was often pointed out how thin was the support for my ideas and how extended the line of reasoning, but I never really doubted the conclusions. The prediction of the DNA unit size and its verification convinced me completely.
Support for a particulate substructure of chromatin came from electron microscopy and from nuclease digestion and sedimentation analysis. Some work on these lines was done even before my own, and though not definitive, was nicely coincident with my ideas. In the years to follow, with colleagues in Cambridge, I proved the existence of the histone octamer and the equivalence of the 200 bp unit with the particle seen in the electron microscope (Kornberg, 1977). This chapter of the chromatin story concluded with the X-ray crystal structure determination of the particle, now known as the nucleosome, showing a histone octamer surrounded by DNA, in near atomic detail (Luger et al., 1997).
İngilizce dilinden Türkçe diline çeviri
Doğum Yeri ve Aile: Francis Bushnell ve Florence Kraemer Sperry Elmwood, küçük bir banliyösünde 20 Ağustos 1913, Hartford, Connecticut tarihi. Baba bankacılık, işletme okulu ve babasının ölümünden sonra eğitimli anne, ben 11 yaşında iken, o yerel lise müdürü asistanı oldu. Bir kardeşi Russell Loomis, genç bir yıl, kimya girdi. Norma Gay Deupree, 28 Aralık 1949 ile evliydi. Biz, bir oğlu Glenn Michael (Tad), 13 Ekim 1953 doğumlu ve 18 Ağustos 1963 doğumlu bir kızı, Janeth Umut var.
Eğitim: Benim erken okula Elmwood, Connecticut ve William Hall West Hartford, Connecticut Yüksek Okulu oldu. 4 yıllık Amos C. Miller Burs Oberlin College katıldı. 1935 yılında İngilizce olarak AB aldıktan sonra, ben Profesör RH Stetson altında bir Psikoloji Yüksek Lisans, 1937, Oberlin 2 yıl daha kaldı. Daha sonra doktora Zooloji anahtarı hazırlamak için Oberlin at büyük bir ek üçüncü yıl aldı Chicago Üniversitesi'nden Profesör Paul A. Weiss altında çalışmak. Doktora aldıktan sonra Chicago, 1941 yılında Harvard Üniversitesi'nde Profesör Karl S. Lashley altında bir Ulusal Araştırma Konseyi Üyesi olarak bir yıl doktora sonrası araştırma yaptı.
04 Eylül 2015 16:08
Roger W. Sperry bilindiği gibi amerikalı biridir. bunun dışında zeki başarılı ve tanınan bir olan Roger W. Sperry genel olarak nöropsikolog alanında yapmış olduğu çalışmalar ile tanınmaktadır. son olarak Roger W. Sperry bilindiği gibi nobel ödüllü bir isimdir.