History of molecular biology 4173711 215534128 2008-05-28T17:01:02Z DOI bot 6652755 Citation maintenance. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. {{Nofootnotes|date=February 2008}} The '''history of molecular biology''' begins in the 1930s with the convergence of various, previously distinct biological disciplines: [[biochemistry]], [[genetics]], [[microbiology]], and [[virology]]. With the hope of understanding life at its most fundamental level, numerous physicists and chemists also took an interest in what would become [[molecular biology]]. In its modern sense, molecular biology attempts to explain the phenomena of [[life]] starting from the macromolecular properties that generate them. Two categories of macromolecules in particular are the focus of the molecular biologist: 1) [[nucleic acid]]s, among which the most famous is [[deoxyribonucleic acid]] (or [[DNA]]), the constituent of [[gene]]s, and 2) [[protein]]s, which are the active agents of living organisms. One definition of the scope of molecular biology therefore is to characterize the structure, function and relationships between these two types of macromolecules. This relatively limited definition will suffice to allow us to establish a date for the so-called "molecular revolution", or at least to establish a chronology of its most fundamental developments. In its earliest manifestations, molecular biology&mdash;the name was coined by [[Warren Weaver]] of the [[Rockefeller Foundation]] in 1938&mdash;was an ideal of physical and chemical explanations of life, rather than a coherent discipline. Following the advent of the [[Mendelian inheritance|Mendelian-chromosome theory of heredity]] in the 1910s and the maturation of [[atomic theory]] and [[quantum mechanics]] in the 1920s, such explanations seemed within reach. Weaver and others encouraged (and funded) research at the intersection of biology, chemistry and physics, while prominent physicists such as [[Niels Bohr]] and [[Erwin Schrödinger]] turned their attention to biological speculation. However, in the 1930s and 1940s it was by no means clear which&mdash;if any&mdash;cross-disciplinary research would bear fruit; work in [[colloid chemistry]], [[biophysics]] and [[radiation biology]], [[crystallography]], and other emerging fields all seemed promising. In 1940, [[George Beadle]] and [[Edward Tatum]] demonstrated the existence of a precise relationship between genes and proteins. In the course of their experiments connecting genetics with biochemistry, they switched from the genetics mainstay ''[[Drosophila melanogaster|Drosophila]]'' to a more appropriate [[model organism]], the fungus ''[[Neurospora crassa|Neurospora]]''; the construction and exploitation of new model organisms would become a recurring theme in the development of molecular biology. In 1944, [[Oswald Avery]], working at the [[Rockefeller University|Rockefeller Institute of New York]], demonstrated that genes are made up of DNA. In 1952, [[Alfred Hershey]] and [[Martha Chase]] confirmed that the genetic material of the [[bacteriophage]], the virus which infects bacteria, is made up of DNA. In 1953, [[James Watson]] and [[Francis Crick]] discovered the double helical structure of the DNA molecule. In 1961, [[Francois Jacob]] and [[Jacques Monod]] hypothesized the existence of an intermediary between DNA and its protein products, which they called [[messenger RNA]]. Between 1961 and 1965, the relationship between the information contained in DNA and the structure of proteins was determined: there is a code, the [[genetic code]], which creates a correspondence between the succession of [[nucleotide]]s in the DNA sequence and a series of [[amino acids]] in proteins. At the beginning of the 1960s, Monod and Jacob also demonstrated how certain specific proteins, called [[Regulation of gene expression|regulative proteins]], latch onto DNA at the edges of the genes and control the [[Transcription (genetics)|transcription]] of these genes into messenger RNA; they direct the "expression" of the genes. The chief discoveries of molecular biology took place in a period of only about twenty-five years. Another fifteen years were required before new and more sophisticated technologies, united today under the name of [[genetic engineering]], would permit the isolation and characterization of genes, in particular those of highly complex organisms. ==The exploration of the molecular dominion== If we evaluate the molecular revolution within the context of biological history, it is easy to note that it is the culmination of a long process which began with the first observations through a microscope. The aim of these early researchers was to understand the functioning of living organisms by describing their organization at the microscopic level. From the end of the 18th century, the characterization of the chemical molecules which make up living beings gained increasingly greater attention, along with the birth of [[physiological chemistry]] in the 19th century, developed by the German chemist [[Justus von Liebig]] and following the birth of biochemistry at the beginning of the 20th, thanks to another German chemist [[Eduard Buchner]]. Between the molecules studied by chemists and the tiny structures visible under the optical microscope, such as the cellular nucleus or the chromosomes, there was an obscure zone, "the world of the ignored dimensions," as it was called by the chemical-physicist [[Wolfgang Ostwald]]. This world is populated by [[colloids]], chemical compounds whose structure and properties were not well defined. The successes of molecular biology derived from the exploration of that unknown world by means of the new technologies developed by chemists and physicists: [[X-ray diffraction]], [[electron microscopy]], [[ultracentrifuge|ultracentrifugization]], and [[electrophoresis]]. These studies revealed the structure and function of the macromolecules. A milestone in that process was the work of [[Linus Pauling#Molecular genetics|Dr. Linus Pauling]], which for the first time linked the specific genetic [[mutation]] in patients with [[sickle cell disease]] to a demonstrated change in an individual protein, the [[hemoglobin]] in the [[erythrocytes]] of [[heterozygous]] or [[homozygous]] individuals. ==The encounter between biochemistry and genetics== The development of molecular biology is also the encounter of two disciplines which made considerable progress in the course of the first thirty years of the twentieth century: biochemistry and genetics. The first studies the structure and function of the molecules which make up living things. Between 1900 and 1940, the central processes of [[metabolism]] were described: the process of [[digestion]] and the absorption of the nutritive elements derived from alimentation, such as the sugars. Every one of these processes is [[catalysis|catalyzed]] by a particular [[enzyme]]. Enzymes are proteins, like the antibodies present in blood or the proteins responsible for muscular contraction. As a consequence, the study of proteins, of their structure and synthesis, became one of the principal objectives of biochemists. The second discipline of biology which developed at the beginning of the 20th century is genetics. After the rediscovery of the laws of [[Gregor Mendel|Mendel]] through the studies of [[Hugo de Vries]], [[Carl Correns]] and [[Erich von Tschermak]] in 1900, this science began to take shape thanks to the adoption by [[Thomas Hunt Morgan]], in 1910, of a model organism for genetic studies, the famous fruit fly ([[Drosophila melanogaster]]). Shortly after, Morgan showed that the genes are localized on chromosomes. Following this discovery, he continued working with Drosophila and, along with numerous other research groups, confirmed the importance of the gene in the life and development of organisms. Nevertheless, the chemical nature of genes and their mechanisms of action remained a mystery. Molecular biologists committed themselves to the determination of the structure, and the description of the complex relations between, genes and proteins. The development of molecular biology was not just the fruit of some sort of intrinsic "necessity" in the history of ideas, but was a characteristically historical phenomenon, with all of its unknowns, imponderables and contingencies: the remarkable developments in physics at the beginning of the 20th century highlighted the relative lateness in development in biology, which became the "new frontier" in the search for knowledge about the empirical world. Moreover, the developments of the [[information theory|theory of information]] and [[cybernetics]] in the 1940s, in response to military exigencies, brought to the new biology a significant number of fertile ideas and, especially, metaphors. The choice of bacteria and of its virus, the bacteriophage, as models for the study of the fundamental mechanisms of life was almost natural - they are the smallest living organisms known to exist - and at the same time the fruit of individual choices. This model owes its success, above all, to the fame and the sense of organization of [[Max Delbrück]], a German physicist, who was able to create a dynamic research group, based in the United States, whose exclusive scope was the study of the bacteriophage: the ''[[School of the Phage]]''. The geographic panorama of the developments of the new biology was conditioned above all by preceding work. The US, where genetics had developed the most rapidly, and the UK, where there was a coexistence of both genetics and biochemical research of highly advanced levels, were in the avant-garde. Germany, the cradle of the revolutions in physics, with the best minds and the most advanced laboratories of genetics in the world, should have had a primary role in the development of molecular biology. But history decided differently: the arrival of the [[Nazism|Nazis]] in 1933 - and, to a less extreme degree, the rigidification of totalitarian measures in [[fascism|fascist]] Italy - caused the emigration of a large number of Jewish and non-Jewish scientists. The majority of them fled to the US or the UK, providing an extra impulse to the scientific dynamism of those nations. These movements ultimately made molecular biology a truly international science from the very beginnings. ==History of DNA biochemistry== {{Double helix2|Name=<big>'''Structure of DNA'''</big>|Photo=|Caption=Francis Crick, lecturing ca. 1979}} The study of DNA is a central part of molecular biology. ===First isolation of DNA=== Working in the 19th century, biochemists initially isolated DNA and RNA (mixed together) from cell nuclei. They were relatively quick to appreciate the polymeric nature of their "nucleic acid" isolates, but realized only later that nucleotides were of two types--one containing [[ribose]] and the other [[deoxyribose]]. It was this subsequent discovery that led to the identification and naming of DNA as a substance distinct from RNA. [[Friedrich Miescher]] (1844-1895) discovered a substance he called "nuclein" in 1869. Somewhat later, he isolated a pure sample of the material now known as DNA from the sperm of salmon, and in 1889 his pupil, [[Richard Altmann]], named it "nucleic acid". This substance was found to exist only in the chromosomes. In 1919 [[Phoebus Levene]] at the [[Rockefeller Institute]] identified the components (the four bases, the sugar and the phosphate chain) and he showed that the components of DNA were linked in the order phosphate-sugar-base. He called each of these units a [[nucleotide]] and suggested the DNA molecule consisted of a string of nucleotide units linked together through the phosphate groups, which are the 'backbone' of the molecule. However Levene thought the chain was short and that the bases repeated in the same fixed order. [[Torbjorn Oskar Caspersson|Torbjorn Caspersson]] and [[Einar Hammersten]] showed that DNA was a polymer. ===Chromosomes and inherited traits=== [[Max Delbrück]], [[Nikolai V. Timofeeff-Ressovsky]], and [[Karl G. Zimmer]] published results in 1935 suggesting that chromosomes are very large molecules the structure of which can be changed by treatment with [[X-ray]]s, and that by so changing their structure it was possible to change the heritable characteristics governed by those chromosomes. In 1937 [[William Astbury]] produced the first [[X-ray diffraction]] patterns from DNA. He was not able to propose the correct structure but the patterns showed that DNA had a regular structure and therefore it might be possible to deduce what this structure was. In 1943, [[Oswald Theodore Avery]] and a team of scientists discovered that traits proper to the "smooth" form of the ''Pneumococcus'' could be transferred to the "rough" form of the same bacteria merely by making the killed "smooth" (S) form available to the live "rough" (R) form. Quite unexpectedly, the living R ''Pneumococcus'' bacteria were transformed into a new strain of the S form, and the transferred S characteristics turned out to be heritable. Avery called the medium of transfer of traits the [[transforming principle]]; he identified DNA as the transforming principle, and not [[protein]] as previously thought. He essentially redid [[Frederick Griffith]]'s experiment. In 1953, [[Alfred Hershey]] and [[Martha Chase]] did an experiment ([[Hershey-Chase experiment]]) that showed, in [[T2 phage]], that DNA is the [[genetic material]] (Hershey shared the Nobel prize with Luria). [[Image:FirstSketchOfDNADoubleHelix.jpg|thumb|[[Francis Crick]]'s first sketch of the [[deoxyribonucleic acid]] double-helix pattern]] ===Discovery of the structure of DNA=== In the 1950s, three groups made it their goal to determine the structure of DNA. The first group to start was at [[King's College London]] and was led by [[Maurice Wilkins]] and was later joined by [[Rosalind Franklin]]. Another group consisting of [[Francis Crick]] and [[James D. Watson]] was at [[University of Cambridge|Cambridge]]. A third group was at [[Caltech]] and was led by [[Linus Pauling]]. Crick and Watson built physical models using metal rods and balls, in which they incorporated the known chemical structures of the nucleotides, as well as the known position of the linkages joining one nucleotide to the next along the polymer. At King's College Maurice Wilkins and Rosalind Franklin examined [[crystallography|X-ray diffraction]] patterns of DNA fibers. Of the three groups, only the London group was able to produce good quality diffraction patterns and thus produce sufficient quantitative data about the structure. ===Helix structure=== In 1948 Pauling discovered that many proteins included helical (see [[alpha helix]]) shapes. Pauling had deduced this structure from X-ray patterns and from attempts to physically model the structures. (Pauling was also later to suggest an incorrect three chain helical DNA structure based on Astbury's data.) Even in the initial diffraction data from DNA by Maurice Wilkins, it was evident that the structure involved helices. But this insight was only a beginning. There remained the questions of how many strands came together, whether this number was the same for every helix, whether the bases pointed toward the helical axis or away, and ultimately what were the explicit angles and coordinates of all the bonds and atoms. Such questions motivated the modeling efforts of Watson and Crick. ===Complementary nucleotides=== In their modeling, Watson and Crick restricted themselves to what they saw as chemically and biologically reasonable. Still, the breadth of possibilities was very wide. A breakthrough occurred in 1952, when [[Erwin Chargaff]] visited Cambridge and inspired Crick with a description of experiments Chargaff had published in 1947. Chargaff had observed that the proportions of the four nucleotides vary between one DNA sample and the next, but that for particular pairs of nucleotides — adenine and thymine, guanine and cytosine — the two nucleotides are always present in equal proportions. [[Image:DNA Model Crick-Watson.jpg|thumb|right|Crick and Watson DNA model built in 1953, was [http://www.farooqhussain.org/projects/ reconstructed] largely from its original pieces in 1973 and donated to the [[Science Museum (London)|National Science Museum]] in London.]] Using [[X-ray diffraction]], as well as other data from [[Rosalind Franklin]] and her information that the bases were paired, [[James D. Watson]] and [[Francis Crick]] arrived at the first accurate model of DNA's molecular structure in 1953, which was accepted through inspection by Rosalind Franklin.<ref>{{cite journal | author = Watson J, Crick F | title = Molecular structure of nucleic acids; a structure for deoxyribose nucleic acid | url=http://profiles.nlm.nih.gov/SC/B/B/Y/W/_/scbbyw.pdf | journal = Nature | volume = 171 | issue = 4356 | pages = 737–8 | year = 1953 | pmid = 13054692 | doi = 10.1038/171737a0}}</ref> In 1962 Watson, Crick, and [[Maurice Wilkins]] jointly received the [[Nobel Prize]] for their determination of the structure of DNA. ==="Central Dogma"=== Watson and Crick's model attracted great interest immediately upon its presentation. Arriving at their conclusion on [[February 21]] [[1953]], Watson and Crick made their first announcement on [[February 28]]. In an influential presentation in 1957, Crick laid out the "[[Central Dogma]]", which foretold the relationship between DNA, RNA, and proteins, and articulated the "sequence hypothesis." A critical confirmation of the replication mechanism that was implied by the double-helical structure followed in 1958 in the form of the [[Meselson-Stahl experiment]]. Work by Crick and coworkers showed that the genetic code was based on non-overlapping triplets of bases, called codons, and [[Har Gobind Khorana]] and others deciphered the [[genetic code]] not long afterward. These findings represent the birth of [[molecular biology]]. ==History of protein biochemistry== ===First isolation and classification=== Proteins were recognized as a distinct class of biological molecules in the eighteenth century by [[Antoine François, comte de Fourcroy|Antoine Fourcroy]] and others. Members of this class (called the "albuminoids", ''Eiweisskörper'', or ''matières albuminoides'') were recognized by their ability to [[coagulate]] or [[flocculation|flocculate]] under various treatments such as heat or acid; well-known examples at the start of the nineteenth century included albumen from [[egg white]]s, [[blood]] [[serum albumin]], [[fibrin]], and [[wheat]] [[gluten]]. The similarity between the cooking of egg whites and the curdling of milk was recognized even in ancient times; for example, the name ''albumen'' for the egg-white protein was coined by [[Pliny the Elder]] from the [[Latin language|Latin]] ''albus ovi'' (egg white). With the advice of [[Jöns Jakob Berzelius]], the Dutch chemist [[Gerhardus Johannes Mulder]] carried out [[elemental analysis|elemental analyses]] of common animal and plant proteins. To everyone's surprise, all proteins had nearly the same [[empirical formula]], roughly C<sub>400</sub>H<sub>620</sub>N<sub>100</sub>O<sub>120</sub> with individual sulfur and phosphorus atoms. Mulder published his findings in two papers (1837,1838) and hypothesized that there was one basic substance (''Grundstoff'') of proteins, and that it was synthesized by plants and absorbed from them by animals in digestion. Berzelius was an early proponent of this theory and proposed the name "protein" for this substance in a letter dated [[10 July]] 1838 <blockquote>The name protein that I propose for the organic oxide of [[fibrin]] and [[albumin]], I wanted to derive from [the [[Greek language|Greek]] word] πρωτειος, because it appears to be the primitive or principal substance of animal nutrition.</blockquote><!--: «Le nom protéine que je vous propose pour l’oxyde organique de la fibrine et de l’albumine, je voulais le dériver de πρωτειος, parce qu’il paraît être la substance primitive ou principale de la nutrition animale.»--> Mulder went on to identify the products of protein degradation such as the [[amino acid]], [[leucine]], for which he found a (nearly correct) molecular weight of 131 [[atomic mass unit|Da]]. ===Purifications and measurements of mass=== The minimum molecular weight suggested by Mulder's analyses was roughly 9 [[atomic mass unit|kDa]], hundreds of times larger than other molecules being studied. Hence, the chemical structure of proteins (their [[primary structure]]) was an active area of research until 1949, when [[Fred Sanger]] sequenced [[insulin]]. The (correct) theory that proteins were linear polymers of [[amino acid]]s linked by [[peptide bond]]s was proposed independently and simultaneously by [[Franz Hofmeister]] and [[Emil Fischer]] at the same conference in 1902. However, some scientists were sceptical that such long [[macromolecule]]s could be stable in solution. Consequently, numerous alternative theories of the protein [[primary structure]] were proposed, e.g., the colloidal hypothesis that proteins were assemblies of small molecules, the [[cyclol]] hypothesis of [[Dorothy Maud Wrinch|Dorothy Wrinch]], the diketopiperazine hypothesis of [[Emil Abderhalden]] and the pyrrol/piperidine hypothesis of Troensgard (1942). Most of these theories had difficulties in accounting for the fact that the digestion of proteins yielded [[peptide]]s and [[amino acid]]s. Proteins were finally shown to be macromolecules of well-defined composition (and not colloidal mixtures) by [[Theodor Svedberg]] using [[analytical ultracentrifugation]]. The possibility that some proteins are non-covalent associations of such macromolecules was shown by [[Gilbert Smithson Adair]] (by measuring the [[osmotic pressure]] of [[hemoglobin]]) and, later, by [[Frederic M. Richards]] in his studies of ribonuclease S. The [[mass spectrometry]] of proteins has long been a useful technique for identifying [[posttranslational modification]]s and, more recently, for probing protein structure. Most proteins are difficult to [[protein purification|purify]] in more than milligram quantities, even using the most modern methods. Hence, early studies focused on proteins that could be purified in large quantities, e.g., those of [[blood]], [[egg white]], various [[toxin]]s, and digestive/metabolic enzymes obtained from [[slaughterhouse]]s. Many techniques of protein purification were developed during [[World War II]] in a project led by [[Edwin Joseph Cohn]] to purify blood proteins to help keep soldiers alive. In the late 1950s, the [[Armour and Company|Armour Hot Dog Co.]] purified 1 kg (= one million milligrams) of pure bovine pancreatic [[ribonuclease A]] and made it freely available to scientists around the world. This generous act made RNase A the main protein for basic research for the next few decades, resulting in several Nobel Prizes. ===Protein folding and first structural models=== The study of protein folding began in 1910 with a famous paper by Henrietta Chick and C. J. Martin, in which they showed that the [[flocculation]] of a protein was composed of two distinct processes: the [[precipitation (chemistry)|precipitation]] of a protein from solution was ''preceded'' by another process called [[Denaturation (biochemistry)|denaturation]], in which the protein became much less soluble, lost its enzymatic activity and became more chemically reactive. In the mid-1920s, [[Mortimer Louis Anson|Tim Anson]] and [[Alfred Mirsky]] proposed that denaturation was a reversible process, a correct hypothesis that was initially lampooned by some scientists as "unboiling the egg". Anson also suggested that denaturation was a two-state ("all-or-none") process, in which one fundamental molecular transition resulted in the drastic changes in solubility, enzymatic activity and chemical reactivity; he further noted that the free energy changes upon denaturation were much smaller than those typically involved in chemical reactions. In 1929, [[Hsien Wu]] hypothesized that denaturation was protein folding, a purely conformational change that resulted in the exposure of amino acid side chains to the solvent. According to this (correct) hypothesis, exposure of aliphatic and reactive side chains to solvent rendered the protein less soluble and more reactive, whereas the loss of a specific conformation caused the loss of enzymatic activity. Although considered plausible, Wu's hypothesis was not immediately accepted, since so little was known of protein structure and enzymology and other factors could account for the changes in solubility, enzymatic activity and chemical reactivity. In the early 1960s, [[Christian B. Anfinsen|Chris Anfinsen]] showed that the folding of [[ribonuclease A]] was fully reversible with no external cofactors needed, verifying the "thermodynamic hypothesis" of protein folding that the folded state represents the global minimum of [[Thermodynamic free energy|free energy]] for the protein. The hypothesis of protein folding was followed by research into the physical interactions that stabilize folded protein structures. The crucial role of [[hydrophobic interaction]]s was hypothesized by [[Dorothy Maud Wrinch|Dorothy Wrinch]] and [[Irving Langmuir]], as a mechanism that might stabilize her [[cyclol]] structures. Although supported by [[J. D. Bernal]] and others, this (correct) hypothesis was rejected along with the cyclol hypothesis, which was disproven in the 1930s by [[Linus Pauling]] (among others). Instead, Pauling championed the idea that protein structure was stabilized mainly by [[hydrogen bond]]s, an idea advanced initially by [[William Astbury]] (1933). Remarkably, Pauling's incorrect theory about H-bonds resulted in his ''correct'' models for the [[secondary structure]] elements of proteins, the [[alpha helix]] and the [[beta sheet]]. The hydrophobic interaction was restored to its correct prominence by a famous article in 1959 by [[Walter Kauzmann]] on [[Denaturation (biochemistry)|denaturation]], based partly on work by [[Kaj Ulrik Linderstrøm-Lang|Kaj Linderstrøm-Lang]]. The ionic nature of proteins was demonstrated by Bjerrum, Weber and [[Arne Tiselius]], but Linderstrom-Lang showed that the charges were generally accessible to solvent and not bound to each other (1949). The [[secondary structure|secondary]] and low-resolution [[tertiary structure]] of globular proteins was investigated initially by hydrodynamic methods, such as [[analytical ultracentrifugation]] and [[flow birefringence]]. Spectroscopic methods to probe protein structure (such as [[circular dichroism]], fluorescence, near-ultraviolet and infrared absorbance) were developed in the 1950s. The first atomic-resolution structures of proteins were solved by [[X-ray crystallography]] in the 1960s and by [[Protein nuclear magnetic resonance spectroscopy|NMR]] in the 1980s. As of 2006, the [[Protein Data Bank]] has nearly 40,000 atomic-resolution structures of proteins. In more recent times, [[cryo-electron microscopy]] of large macromolecular assemblies and computational [[protein structure prediction]] of small protein [[structural domain|domains]] are two methods approaching atomic resolution. <!-- Add stuff about discovery of amino acids --> <!-- Solubility studies: Hofmeister, EJ Cohn --> <!-- Functional roles of proteins, e.g., enzymology --> <!-- Crystallization of proteins as purification trick? --> <!-- Enzymes = proteins? --> <!--needs info on the importance of the triplet code--> ==See also== *[[History of biology]] *[[History of biotechnology]] *[[History of genetics]] ==References== {{reflist}} * Fruton, Joseph. ''Proteins, Genes, Enzymes: The Interplay of Chemistry and Biology''. New Haven: Yale University Press. 1999. ISBN 0-300-07608-8 * [[Lily E. Kay]], ''The Molecular Vision of Life: Caltech, the Rockefeller Foundation, and the Rise of the New Biology'', Oxford University Press, Reprint 1996 * Morange, Michel. ''A History of Molecular Biology''. Cambridge, MA: Harvard University Press. 1998. {{History of biology}} {{DEFAULTSORT:Molecular biology, history of}} [[Category:History of biology]] [[Category:History of chemistry]] [[zh:分子生物學史]]