Discovery of DNA Double Helix: Watson and Crick | Learn Science at Scitable Aa Aa Aa Many people believe that American biologist James Watson and English physicist Francis Crick discovered DNA in the 1950s. In reality, this is not the case. Rather, DNA was first identified in the late 1860s by Swiss chemist Friedrich Miescher. Then, in the decades following Miescher's discovery, other scientists--notably, Phoebus Levene and Erwin Chargaff--carried out a series of research efforts that revealed additional details about the DNA molecule, including its primary chemical components and the ways in which they joined with one another. Without the scientific foundation provided by these pioneers, Watson and Crick may never have reached their groundbreaking conclusion of 1953: that the DNA molecule exists in the form of a three-dimensional double helix. The First Piece of the Puzzle: Miescher Discovers DNA Although few people realize it, 1869 was a landmark year in genetic research, because it was the year in which Swiss physiological chemist Friedrich Miescher first identified what he called "nuclein" inside the nuclei of human white blood cells.

(The term "nuclein" was later changed to "nucleic acid" and eventually to "deoxyribonucleic acid," or "DNA.") Miescher's plan was to isolate and characterize not the nuclein (which nobody at that time realized existed) but instead the protein components of leukocytes (white blood cells). Miescher thus made arrangements for a local surgical clinic to send him used, pus-coated patient bandages; once he received the bandages, he planned to wash them, filter out the leukocytes, and extract and identify the various proteins within the white blood cells. But when he came across a substance from the cell nuclei that had chemical properties unlike any protein, including a much higher phosphorous content and resistance to proteolysis (protein digestion), Miescher realized that he had discovered a new substance (Dahm, 2008). Sensing the importance of his findings, Miescher wrote, "It seems probable to me that a whole family of such slightly varying phosphorous-containing substances will appear, as a group of nucleins, equivalent to proteins" (Wolf, 2003).

More than 50 years passed before the significance of Miescher's discovery of nucleic acids was widely appreciated by the scientific community. For instance, in a 1971 essay on the history of nucleic acid research, Erwin Chargaff noted that in a 1961 historical account of nineteenth-century science, Charles Darwin was mentioned 31 times, Thomas Huxley 14 times, but Miescher not even once. This omission is all the more remarkable given that, as Chargaff also noted, Miescher's discovery of nucleic acids was unique among the discoveries of the four major cellular components (i.e., proteins, lipids, polysaccharides, and nucleic acids) in that it could be "dated precisely... [to] one man, one place, one date." Laying the Groundwork: Levene Investigates the Structure of DNA Meanwhile, even as Miescher's name fell into obscurity by the twentieth century, other scientists continued to investigate the chemical nature of the molecule formerly known as nuclein. One of these other scientists was Russian biochemist Phoebus Levene.

A physician turned chemist, Levene was a prolific researcher, publishing more than 700 papers on the chemistry of biological molecules over the course of his career. Levene is credited with many firsts. For instance, he was the first to discover the order of the three major components of a single nucleotide (phosphate-sugar-base); the first to discover the carbohydrate component of RNA (ribose); the first to discover the carbohydrate component of DNA (deoxyribose); and the first to correctly identify the way RNA and DNA molecules are put together. During the early years of Levene's career, neither Levene nor any other scientist of the time knew how the individual nucleotide components of DNA were arranged in space; discovery of the sugar-phosphate backbone of the DNA molecule was still years away. The large number of molecular groups made available for binding by each nucleotide component meant that there were numerous alternate ways that the components could combine. Several scientists put forth suggestions for how this might occur, but it was Levene's "polynucleotide" model that proved to be the correct one.

Based upon years of work using hydrolysis to break down and analyze yeast nucleic acids, Levene proposed that nucleic acids were composed of a series of nucleotides, and that each nucleotide was in turn composed of just one of four nitrogen-containing bases, a sugar molecule, and a phosphate group. Levene made his initial proposal in 1919, discrediting other suggestions that had been put forth about the structure of nucleic acids. In Levene's own words, "New facts and new evidence may cause its alteration, but there is no doubt as to the polynucleotide structure of the yeast nucleic acid" (1919). Indeed, many new facts and much new evidence soon emerged and caused alterations to Levene's proposal. One key discovery during this period involved the way in which nucleotides are ordered. Levene proposed what he called a tetranucleotide structure, in which the nucleotides were always linked in the same order (i.e., G-C-T-A-G-C-T-A and so on).

However, scientists eventually realized that Levene's proposed tetranucleotide structure was overly simplistic and that the order of nucleotides along a stretch of DNA (or RNA) is, in fact, highly variable. Despite this realization, Levene's proposed polynucleotide structure was accurate in many regards. For example, we now know that DNA is in fact composed of a series of nucleotides and that each nucleotide has three components: a phosphate group; either a ribose (in the case of RNA) or a deoxyribose (in the case of DNA) sugar; and a single nitrogen-containing base. We also know that there are two basic categories of nitrogenous bases: the purines (adenine [A] and guanine [G]), each with two fused rings, and the pyrimidines (cytosine [C], thymine [T], and uracil [U]), each with a single ring. Furthermore, it is now widely accepted that RNA contains only A, G, C, and U (no T), whereas DNA contains only A, G, C, and T (no U) (Figure 1). Figure 1: The chemical structure of a nucleotide.

A single nucleotide is made up of three components: a nitrogen-containing base, a five-carbon sugar, and a phosphate group. The nitrogenous base is either a purine or a pyrimidine. The five-carbon sugar is either a ribose (in RNA) or a deoxyribose (in DNA) molecule. Watson and Crick Discovered DNA 60 Years Ago Today Watson and Crick Discovered DNA 60 Years Ago Today On the morning of February 28th, 1953, two men quietly made history in the Cavendish Laboratory of Cambridge University. Sixty years ago today, Watson and Crick discovered DNA—and changed the face of biological science in the process. Advertisement Along with Maurice Wilkins and Rosalind Franklin—both unsung heroes in the discovery—the pair used X-ray diffraction to interrogate the insides of living cells. They found a twisted pair of strands of deoxyribonucleic acid, intertwined in such a way that they could pull apart, replicate themselves, and pass their genetic code from old cells to new. They had found the basic building block of all life—and they knew it.

At the time, Watson declared the finding "so beautiful it had to be true", and so it remains. They went on to publish their findings in Nature on 25 April 1953, to much fanfare. But despite their confidence, they were restrained in the way they wrote about the finding, simply stating: Advertisement "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material." That single, modest sentence is now a bedrock of biological science and medicine. So the Nobel Prize in Physiology or Medicine, awarded to them in 1962, was richly deserved (sadly Wilkins and Franklin weren't honored at the time, but that's quite another story). So Watson, Crick, and everybody that helped you: congratulations on perhaps the biggest discovery biology has ever seen. The Discovery of the Molecular Structure of DNA - The Double Helix The Discovery of the Molecular Structure of DNA - The Double Helix A Scientific Breakthrough The sentence "This structure has novel features which are of considerable biological interest" may be one of science's most famous understatements.

It appeared in April 1953 in the scientific paper where James Watson and Francis Crick presented the structure of the DNA-helix, the molecule that carries genetic information from one generation to the other. Nine years later, in 1962, they shared the Nobel Prize in Physiology or Medicine with Maurice Wilkins, for solving one of the most important of all biological riddles. Half a century later, important new implications of this contribution to science are still coming to light. What is DNA? The work of many scientists paved the way for the exploration of DNA. Way back in 1868, almost a century before the Nobel Prize was awarded to Watson, Crick and Wilkins, a young Swiss physician named Friedrich Miescher, isolated something no one had ever seen before from the nuclei of cells. He called the compound "nuclein." This is today called nucleic acid, the "NA" in DNA (deoxyribo-nucleic-acid) and RNA (ribo-nucleic-acid). Francis Crick and James Watson, 1953. Photo: Cold Spring Harbor Laboratory Archives Maurice Wilkins.

Two years earlier, the Czech monk Gregor Mendel, had finished a series of experiments with peas. His observations turned out to be closely connected to the finding of nuclein. Mendel was able to show that certain traits in the peas, such as their shape or color, were inherited in different packages. These packages are what we now call genes. For a long time the connection between nucleic acid and genes was not known. But in 1944 the American scientist Oswald Avery managed to transfer the ability to cause disease from one strain of bacteria to another. But not only that: the previously harmless bacteria could also pass the trait along to the next generation. What Avery had moved was nucleic acid. This proved that genes were made up of nucleic acid. Solving the Puzzle In the late 1940's, the members of the scientific community were aware that DNA was most likely the molecule of life, even though many were skeptical since it was so "simple." They also knew that DNA included different amounts of the four bases adenine, thymine, guanine and cytosine (usually abbreviated A, T, G and C), but nobody had the slightest idea of what the molecule might look like.

In order to solve the elusive structure of DNA, a couple of distinct pieces of information needed to be put together. One was that the phosphate backbone was on the outside with bases on the inside; another that the molecule was a double helix. It was also important to figure out that the two strands run in opposite directions and that the molecule had a specific base pairing. As in the solving of other complex problems, the work of many people was needed to establish the full picture. The original DNA model by Watson and Crick. Photo: Cold Spring Harbor Laboratory Archives Using X-rays to See Through DNA Watson and Crick used stick-and-ball models to test their ideas on the possible structure of DNA. Other scientists used experimental methods instead. Among them were Rosalind Franklin and Maurice Wilkins, who were using X-ray diffraction to understand the physical structure of the DNA molecule. When you shine X-rays on any kind of crystal – and some biological molecules, such as DNA, can form crystals if treated in certain ways – the invisible rays bounce off the sample. The rays then create complex patterns on photographic film. By looking at the patterns, it is possible to figure out important clues about the structures that make up the crystal. "Photograph 51".

X-ray diffraction photo of a DNA molecule, structure B. Photo: Cold Spring Harbor Laboratory Archives A Three-Helical Structure? The scientist Linus Pauling was eager to solve the mystery of the shape of DNA. In 1954 he became a Nobel Laureate in Chemistry for his ground-breaking work on chemical bonds and the structure of molecules and crystals. In early 1953 he had published a paper where he proposed a triple-helical structure for DNA. Watson and Crick had also previously worked out a three-helical model, in 1951. But their theory was wrong. Their mistake was partly based on Watson having misremembered a talk by Rosalind Franklin where she reported that she had established the water content of DNA by using X-ray crystallographic methods. But Watson did not take notes, and remembered the numbers incorrectly. Instead, it was Franklin's famous "photograph 51" that finally revealed the helical structure of DNA to Watson and Crick in 1953. This picture of DNA that had been crystallized under moist conditions shows a fuzzy X in the middle of the molecule, a pattern indicating a helical structure.

Model of the alpha helix, 1951. Photo: Oregon State University's Special Collections Specific Base-Pairing The base-pairing mystery had been partly solved by the biochemist Erwin Chargoff some years earlier. In 1949 he showed that even though different organisms have different amounts of DNA, the amount of adenine always equals the amount of thymine. The same goes for the pair guanine and cytosine. For example, human DNA contains about 30 percent each of adenine and thymine, and 20 percent each of guanine and cytosine. With this information at hand Watson was able to figure out the pairing rules. On the 21st of February 1953 he had the key insight, when he saw that the adenine-thymine bond was exactly as long as the cytosine-guanine bond. If the bases were paired in this way, each rung of the twisted ladder in the helix would be of equal length, and the sugar-phosphate backbone would be smooth.

Structure Shows Action "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material" wrote Watson and Crick in the scientific paper that was published in Nature, April 25, 1953. This was indeed a breakthrough in the study of how genetic material passes from generation to generation. Once the model was established, its mere structure hinted that DNA was indeed the carrier of the genetic code and thus the key molecule of heredity, developmental biology and evolution. The specific base pairing underlies the perfect copying of the molecule, which is essential for heredity. During cell division, the DNA molecule is able to "unzip" into two pieces. One new molecule is formed from each half-ladder, and due to the specific pairing this gives rise to two identical daughter copies from each parent molecule. We All Share the Same Building Blocks DNA is a winning formula for packaging genetic material. Therefore almost all organisms – bacteria, plants, yeast and animals – carry genetic information encapsulated as DNA. One exception is some viruses that use RNA instead. Different species need different amounts of DNA. Therefore the copying of the DNA that precedes cell division differs between organisms. For example, the DNA in E.

coli bacteria is made up of 4 million base pairs and the whole genome is thus one millimeter long. The single-cell bacterium can copy its genome and divide into two cells once every 20 minutes. The DNA of humans, on the other hand, is composed of approximately 3 billion base pairs, making up a total of almost a meter-long stretch of DNA in every cell in our bodies. In order to fit, the DNA must be packaged in a very compact form. In E. coli the single circular DNA molecule is curled up in a condensed fashion, whereas the human DNA is packaged in 23 distinct chromosome pairs. Here the genetic material is tightly rolled up on structures called histones. A New Biological Era This knowledge of how genetic material is stored and copied has given rise to a new way of looking at and manipulating biological processes, called molecular biology. With the help of so-called restriction enzymes, molecules that cut the DNA at particular stretches, pieces of DNA can be cut out or inserted at different places. In basic science, where you want to understand the role of all the different genes in humans and animals, new techniques have been developed. For one thing, it is now possible to make mice that are genetically modified and lack particular genes.

By studying these animals scientists try to figure out what that gene may be used for in normal mice. This is called the knockout technique, since stretches of DNA have been taken away, or knocked out. Scientists have also been able to insert new bits of DNA into cells that lack particular pieces of genes or whole genes. With this new DNA, the cell becomes capable of producing gene products it could not make before. The hope is that, in the future, diseases that arise due to the lack of a particular protein could be treated by this kind of gene therapy. Photo: Cold Spring Harbor Laboratory Archives Many voices have argued that the Nobel Prize should also have been awarded to Rosalind Franklin, since her experimental data provided a very important piece of evidence leading to the solving of the DNA structure. In a recent interview in the magazine Scientific American, Watson himself suggested that it might have been a good idea to give Wilkins and Franklin the Nobel Prize in Chemistry, and him and Crick the Nobel Prize in Physiology or Medicine – in that way all four would have been honored. Rosalind Franklin died in 1958. As a rule only living persons can be nominated for the Nobel Prize, so the 1962 Nobel Prize was out of the question.

The Nobel archives, at the Nobel Prize-awarding institutions, that among other things contain the nominations connected to the prizes, are held closed. But 50 years after a particular prize had been awarded, the archives concerning the nominees are released. Therefore, in 2008 it was possible to see whether Rosalind Franklin ever was a nominee for the Nobel Prize concerning the DNA helix. The answer is that no one ever nominated her - neither for the Nobel Prize in Physiology or Medicine nor in Chemistry. The DNA-Helix The sugar-phosphate backbone is on the outside and the four different bases are on the inside of the DNA molecule. The two strands of the double helix are anti-parallel, which means that they run in opposite directions. The sugar-phosphate backbone is on the outside of the helix, and the bases are on the inside. The backbone can be thought of as the sides of a ladder, whereas the bases in the middle form the rungs of the ladder. Each rung is composed of two base pairs. Either an adenine-thymine pair that form a two-hydrogen bond together, or a cytosine-guanine pair that form a three-hydrogen bond. The base pairing is thus restricted.

This restriction is essential when the DNA is being copied: the DNA-helix is first "unzipped" in two long stretches of sugar-phosphate backbone with a line of free bases sticking up from it, like the teeth of a comb. Each half will then be the template for a new, complementary strand. Biological machines inside the cell put the corresponding free bases onto the split molecule and also "proof-read" the result to find and correct any mistakes. After the doubling, this gives rise to two exact copies of the original DNA molecule. The coding regions in the DNA strand, the genes, make up only a fraction of the total amount of DNA. The stretches that flank the coding regions are called introns, and consist of non-coding DNA. Introns were looked upon as junk in the early days. Today, biologists and geneticists believe that this non-coding DNA may be essential in order to expose the coding regions and to regulate how the genes are expressed.

By Lotta Fredholm, Science Journalist First published 30 September 2003 READ MORE The Francis Crick Papers: The Discovery of the Double Helix, 1951-1953 The Discovery of the Double Helix, 1951-1953 Visuals The discovery in 1953 of the double helix, the twisted-ladder structure of deoxyribonucleic acid (DNA), by James Watson and Francis Crick marked a milestone in the history of science and gave rise to modern molecular biology, which is largely concerned with understanding how genes control the chemical processes within cells. In short order, their discovery yielded ground-breaking insights into the genetic code and protein synthesis. During the 1970s and 1980s, it helped to produce new and powerful scientific techniques, specifically recombinant DNA research, genetic engineering, rapid gene sequencing, and monoclonal antibodies, techniques on which today's multi-billion dollar biotechnology industry is founded.

Major current advances in science, namely genetic fingerprinting and modern forensics, the mapping of the human genome, and the promise, yet unfulfilled, of gene therapy, all have their origins in Watson and Crick's inspired work. The double helix has not only reshaped biology, it has become a cultural icon, represented in sculpture, visual art, jewelry, and toys. Researchers working on DNA in the early 1950s used the term "gene" to mean the smallest unit of genetic information, but they did not know what a gene actually looked like structurally and chemically, or how it was copied, with very few errors, generation after generation. In 1944, Oswald Avery had shown that DNA was the "transforming principle," the carrier of hereditary information, in pneumococcal bacteria. Nevertheless, many scientists continued to believe that DNA had a structure too uniform and simple to store genetic information for making complex living organisms. The genetic material, they reasoned, must consist of proteins, much more diverse and intricate molecules known to perform a multitude of biological functions in the cell.

Crick and Watson recognized, at an early stage in their careers, that gaining a detailed knowledge of the three-dimensional configuration of the gene was the central problem in molecular biology. Without such knowledge, heredity and reproduction could not be understood. They seized on this problem during their very first encounter, in the summer of 1951, and pursued it with single-minded focus over the course of the next eighteen months. This meant taking on the arduous intellectual task of immersing themselves in all the fields of science involved: genetics, biochemistry, chemistry, physical chemistry, and X-ray crystallography. Drawing on the experimental results of others (they conducted no DNA experiments of their own), taking advantage of their complementary scientific backgrounds in physics and X-ray crystallography (Crick) and viral and bacterial genetics (Watson), and relying on their brilliant intuition, persistence, and luck, the two showed that DNA had a structure sufficiently complex and yet elegantly simple enough to be the master molecule of life. Other researchers had made important but seemingly unconnected findings about the composition of DNA; it fell to Watson and Crick to unify these disparate findings into a coherent theory of genetic transfer.

The organic chemist Alexander Todd had determined that the backbone of the DNA molecule contained repeating phosphate and deoxyribose sugar groups. The biochemist Erwin Chargaff had found that while the amount of DNA and of its four types of bases--the purine bases adenine (A) and guanine (G), and the pyrimidine bases cytosine (C) and thymine(T)--varied widely from species to species, A and T always appeared in ratios of one-to-one, as did G and C. Maurice Wilkins and Rosalind Franklin had obtained high-resolution X-ray images of DNA fibers that suggested a helical, corkscrew-like shape. Linus Pauling, then the world's leading physical chemist, had recently discovered the single-stranded alpha helix, the structure found in many proteins, prompting biologists to think of helical forms. Moreover, he had pioneered the method of model building in chemistry by which Watson and Crick were to uncover the structure of DNA. Indeed, Crick and Watson feared that they would be upstaged by Pauling, who proposed his own model of DNA in February 1953, although his three-stranded helical structure quickly proved erroneous.

The time, then, was ripe for their discovery. After several failed attempts at model building, including their own ill-fated three-stranded version and one in which the bases were paired like with like (adenine with adenine, etc.), they achieved their break-through. Jerry Donohue, a visiting physical chemist from the United States who shared Watson and Crick's office for the year, pointed out that the configuration for the rings of carbon, nitrogen, hydrogen, and oxygen (the elements of all four bases) in thymine and guanine given in most textbooks of chemistry was incorrect. On February 28, 1953, Watson, acting on Donohue's advice, put the two bases into their correct form in cardboard models by moving a hydrogen atom from a position where it bonded with oxygen to a neighboring position where it bonded with nitrogen. While shifting around the cardboard cut-outs of the accurate molecules on his office table, Watson realized in a stroke of inspiration that A, when joined with T, very nearly resembled a combination of C and G, and that each pair could hold together by forming hydrogen bonds.

If A always paired with T, and likewise C with G, then not only were Chargaff's rules (that in DNA, the amount of A equals that of T, and C that of G) accounted for, but the pairs could be neatly fitted between the two helical sugar-phosphate backbones of DNA, the outside rails of the ladder. The bases connected to the two backbones at right angles while the backbones retained their regular shape as they wound around a common axis, all of which were structural features demanded by the X-ray evidence. Similarly, the complementary pairing of the bases was compatible with the fact, also established by the X-ray diffraction pattern, that the backbones ran in opposite direction to each other, one up, the other down. Watson and Crick published their findings in a one-page paper, with the understated title "A Structure for Deoxyribose Nucleic Acid," in the British scientific weekly Nature on April 25, 1953, illustrated with a schematic drawing of the double helix by Crick's wife, Odile. A coin toss decided the order in which they were named as authors.

Foremost among the "novel features" of "considerable biological interest" they described was the pairing of the bases on the inside of the two DNA backbones: A=T and C=G. The pairing rule immediately suggested a copying mechanism for DNA: given the sequence of the bases in one strand, that of the other was automatically determined, which meant that when the two chains separated, each served as a template for a complementary new chain. Watson and Crick developed their ideas about genetic replication in a second article in Nature, published on May 30, 1953. The two had shown that in DNA, form is function: the double-stranded molecule could both produce exact copies of itself and carry genetic instructions. During the following years, Crick elaborated on the implications of the double-helical model, advancing the hypothesis, revolutionary then but widely-accepted since, that the sequence of the bases in DNA forms a code by which genetic information can be stored and transmitted. Although recognized today as one of the seminal scientific papers of the twentieth century, Watson and Crick's original article in Nature was not frequently cited at first.

Its true significance became apparent, and its circulation widened, only towards the end of the 1950s, when the structure of DNA they had proposed was shown to provide a mechanism for controlling protein synthesis, and when their conclusions were confirmed in the laboratory by Matthew Meselson, Arthur Kornberg, and others. Crick himself immediately understood the significance of his and Watson's discovery. As Watson recalled, after their conceptual breakthrough on February 28, 1953, Crick declared to the assembled lunch patrons at The Eagle that they had "found the secret of life." Crick himself had no memory of such an announcement, but did recall telling his wife that evening "that we seemed to have made a big discovery." He revealed that "years later she told me that she hadn't believed a word of it." As he recounted her words, "You were always coming home and saying things like that, so naturally I thought nothing of it." Retrospective accounts of the discovery of the structure of DNA have continued to elicit a measure of controversy.

Crick was incensed at Watson's depiction of their collaboration in The Double Helix (1968), castigating the book as a betrayal of their friendship, an intrusion into his privacy, and a distortion of his motives. He waged an unsuccessful campaign to prevent its publication. He eventually became reconciled to Watson's bestseller, concluding that if it presented an unfavorable portrait of a scientist, it was of Watson, not of himself. A more enduring controversy has been generated by Watson and Crick's use of Rosalind Franklin's crystallographic evidence of the structure of DNA, which was shown to them, without her knowledge, by her estranged colleague, Maurice Wilkins, and by Max Perutz. Her evidence demonstrated that the two sugar-phosphate backbones lay on the outside of the molecule, confirmed Watson and Crick's conjecture that the backbones formed a double helix, and revealed to Crick that they were antiparallel. Franklin's superb experimental work thus proved crucial in Watson and Crick's discovery. Yet, they gave her scant acknowledgment. Even so, Franklin bore no resentment towards them. She had presented her findings at a public seminar to which she had invited the two.

She soon left DNA research to study tobacco mosaic virus. She became friends with both Watson and Crick, and spent her last period of remission from ovarian cancer in Crick's house (Franklin died in 1958). Crick believed that he and Watson used her evidence appropriately, while admitting that their patronizing attitude towards her, so apparent in The Double Helix, reflected contemporary conventions of gender in science. A Science Odyssey: People and Discoveries: Watson and Crick describe structure of DNA Watson and Crick describe structure of DNA 1953 Photo: Model of DNA molecule In the late nineteenth century, a German biochemist found the nucleic acids, long-chain polymers of nucleotides, were made up of sugar, phosphoric acid, and several nitrogen-containing bases. Later it was found that the sugar in nucleic acid can be ribose or deoxyribose, giving two forms: RNA and DNA. In 1943, American Oswald Avery proved that DNA carries genetic information. He even suggested DNA might actually be the gene. Most people at the time thought the gene would be protein, not nucleic acid, but by the late 1940s, DNA was largely accepted as the genetic molecule.

Scientists still needed to figure out this molecule's structure to be sure, and to understand how it worked. In 1948, Linus Pauling discovered that many proteins take the shape of an alpha helix, spiraled like a spring coil. In 1950, biochemist Erwin Chargaff found that the arrangement of nitrogen bases in DNA varied widely, but the amount of certain bases always occurred in a one-to-one ratio. These discoveries were an important foundation for the later description of DNA. In the early 1950s, the race to discover DNA was on. At Cambridge University, graduate student Francis Crick and research fellow James Watson (b. 1928) had become interested, impressed especially by Pauling's work. Meanwhile at King's College in London, Maurice Wilkins (b. 1916) and Rosalind Franklin were also studying DNA. The Cambridge team's approach was to make physical models to narrow down the possibilities and eventually create an accurate picture of the molecule. The King's team took an experimental approach, looking particularly at x-ray diffraction images of DNA. In 1951, Watson attended a lecture by Franklin on her work to date.

She had found that DNA can exist in two forms, depending on the relative humidity in the surrounding air. This had helped her deduce that the phosphate part of the molecule was on the outside. Watson returned to Cambridge with a rather muddy recollection of the facts Franklin had presented, though clearly critical of her lecture style and personal appearance. Based on this information, Watson and Crick made a failed model. It caused the head of their unit to tell them to stop DNA research. But the subject just kept coming up. Franklin, working mostly alone, found that her x-ray diffractions showed that the "wet" form of DNA (in the higher humidity) had all the characteristics of a helix. She suspected that all DNA was helical but did not want to announce this finding until she had sufficient evidence on the other form as well. Wilkins was frustrated. In January, 1953, he showed Franklin's results to Watson, apparently without her knowledge or consent.

Crick later admitted, "I'm afraid we always used to adopt -- let's say, a patronizing attitude towards her." Watson and Crick took a crucial conceptual step, suggesting the molecule was made of two chains of nucleotides, each in a helix as Franklin had found, but one going up and the other going down. Crick had just learned of Chargaff's findings about base pairs in the summer of 1952. He added that to the model, so that matching base pairs interlocked in the middle of the double helix to keep the distance between the chains constant. Watson and Crick showed that each strand of the DNA molecule was a template for the other. During cell division the two strands separate and on each strand a new "other half" is built, just like the one before. This way DNA can reproduce itself without changing its structure -- except for occasional errors, or mutations. The structure so perfectly fit the experimental data that it was almost immediately accepted. DNA's discovery has been called the most important biological work of the last 100 years, and the field it opened may be the scientific frontier for the next 100.

By 1962, when Watson, Crick, and Wilkins won the Nobel Prize for physiology/medicine, Franklin had died. The Nobel Prize only goes to living recipients, and can only be shared among three winners. Were she alive, would she have been included in the prize? Related Features Watson and Crick discover chemical structure of DNA - Feb 28, 1953 - HISTORY.com This Day In History: 02/28/1953 - DNA Structure Discovered On February 28th many historical events occurred. These events are recapped by Russell Mitchell in this video clip from "This Day in History". The discovery of DNA by James Watson and Frances Crick being a major one for the scientific community. Not only was DNA discovered on this day, but the Republican Party was founded in Wisconsin. The well-known album Thriller by Michael Jackson won eight Emmy awards as well. Lead Story Watson and Crick discover chemical structure of DNA Share this: Watson and Crick discover chemical structure of DNA Author Watson and Crick discover chemical structure of DNA URL Publisher A+E Networks On this day in 1953, Cambridge University scientists James D. Watson and Frances H.C.

Crick announce that they have determined the double-helix structure of DNA, the molecule containing human genes. Though DNA–short for deoxyribonucleic acid–was discovered in 1869, its crucial role in determining genetic inheritance wasn’t demonstrated until 1943. In the early 1950s, Watson and Crick were only two of many scientists working on figuring out the structure of DNA. California chemist Linus Pauling suggested an incorrect model at the beginning of 1953, prompting Watson and Crick to try and beat Pauling at his own game. On the morning of February 28, they determined that the structure of DNA was a double-helix polymer, or a spiral of two DNA strands, each containing a long chain of monomer nucleotides, wound around each other. According to their findings, DNA replicated itself by separating into individual strands, each of which became the template for a new double helix.

In his best-selling book, The Double Helix (1968), Watson later claimed that Crick announced the discovery by walking into the nearby Eagle Pub and blurting out that “we had found the secret of life.” The truth wasn’t that far off, as Watson and Crick had solved a fundamental mystery of science–how it was possible for genetic instructions to be held inside organisms and passed from generation to generation. Watson and Crick’s solution was formally announced on April 25, 1953, following its publication in that month’s issue of Nature magazine. The article revolutionized the study of biology and medicine. Among the developments that followed directly from it were pre-natal screening for disease genes; genetically engineered foods; the ability to identify human remains; the rational design of treatments for diseases such as AIDS; and the accurate testing of physical evidence in order to convict or exonerate criminals. Crick and Watson later had a falling-out over Watson’s book, which Crick felt misrepresented their collaboration and betrayed their friendship.

A larger controversy arose over the use Watson and Crick made of research done by another DNA researcher, Rosalind Franklin, whose colleague Maurice Wilkins showed her X-ray photographic work to Watson just before he and Crick made their famous discovery. When Crick and Watson won the Nobel Prize in 1962, they shared it with Wilkins. Franklin, who died in 1958 of ovarian cancer and was thus ineligible for the award, never learned of the role her photos played in the historic scientific breakthrough. Related Videos DNA double helix: discovery that led to 60 years of biological revolution | Adam Rutherford | Science | The Guardian DNA double helix: discovery that led to 60 years of biological revolution Adam Rutherford Six decades after DNA's shapely curves were first revealed, no aspect of biology is now above modification, remix or redesign On 25 April 1953, Francis Crick (left) and James Watson (right) published a paper in Nature describing the double helix structure of DNA.

Photograph: AP Thursday 25 April 2013 02.01 EDT First published on Thursday 25 April 2013 02.01 EDT Share on Messenger Close The myth is that science proceeds in fits and starts, with eureka moments delivering revelation and revolution. The reality is usually much more mundane: a case of scientists grinding out small, incremental advances. But the publication 60 years ago of Francis Crick and James Watson's celebrated structure of DNA – the twisted ladder of the double helix – can legitimately be regarded as a turning point: our understanding of life was changed forever that day, and the modern era of biology began. "It has not escaped our notice," they wrote in a brief paper in the journal Nature , that the double helix "immediately suggests a copying mechanism for the genetic material." And so it does. This elegant spiral, first drawn by Crick's wife Odile, depicts life's most famous molecule. Nowadays it is part of our culture: in films, as art, on shampoo adverts. We now know that DNA is a dynamic, tortuous coil, constantly shuffling and unwinding, bustling with activity as it enacts its many programs.

Since 1953, biology has evolved into a global industry, with our ever-increasing command over DNA at its core. We have seen the emergence of genetic modification and now synthetic biology – for both scientific and commercial gain – each with its own mire of ongoing legal wrangles . And now we are entering the post-DNA era. In the past couple of years, the nature of DNA itself has been modified, its alphabet mutated and its function reinvented for non-biological uses. DNA's operation is determined by its shape. Each rung of the ladder is made up of a pair of two of the four letters of the DNA alphabet – A, T, C and G. But A will only pair with T, and C only with G. So if you were to split the ladder in two, breaking the paired rungs, then on each of these struts you would have all the information needed to replace the missing one. Hence, from one DNA molecule, you can make two identical molecules. This is happening right now inside you as the cells that make up your body divide, at a rate of around 3,000 letters a minute (bacteria can do it 10 times faster).

And the same process has been happening continuously in every cell that has ever existed on Earth. DNA in living cells, as far as we know, is universal, and combined with Darwin's theory of evolution we have a robust model of how life is, and how it came to be, its origins almost 4bn years ago. DNA is a code, a means of storing biological data, in the form of genes. The code was systematically cracked in the 1960s, revealing that life is breathtakingly conservative. If DNA is an alphabet, then the words it spells out are amino acids, the building blocks of proteins. And yet only 20 amino acids are encoded by DNA in all life forms. The same alphabet, the same encryption, the same lexicon are applied in every bacterium or blue whale, in you, a sunflower and a mushroom. It is this uniformity that spawned the industrial revolution of biotechnology that we are in the throes of today. In California in the early 1970s, scientists invented ways to swap chunks of DNA between species, so that they acquired specific characteristics by design.

Humans have been doing something similar for 10,000 years through breeding and farming, but with the advent of DNA editing tools, we were suddenly no longer bound by the limitations of creatures that could have sex. Genetic modification has become a mainstay of almost every aspect of the life sciences, and provided innumerable advances in our understanding of how life and diseases work. DNA structure Photograph: Graphic This century, the descendant of genetic modification has emerged as synthetic biology . This takes the principles of gene tinkering, and, just as the pioneers of electronics did, standardises the components so that creating new technologies becomes easier. In the summer, we will see the largest synthetic biology meeting in the world at Imperial College London, where the creators of this rapidly maturing field will gather to turn the remixed tools of evolution into ever-more sophisticated circuitry to address global issues including food, fuel and food production. On paper, this circuitry looks like electronics, with transistor-like junctions and gates. But it is in fact DNA, carefully designed and assembled to perform specific logical functions. We're 10 years on from the completion of the Human Genome Project , initially led by Watson, the complete read-through of all 3bn letters of our own code.

That yielded many surprises, including that we're a long way from understanding how our genomes work. But we also entered the legal swamp of DNA patenting , the idea – currently law – that your genes can be owned by someone else. Two breast cancer genes are the subjects of the key legal test case, which is being addressed by the US supreme court this week, with globally significant ramifications. The pioneers of genetics changed how science itself is done. The Human Genome Project launched a new style of big science — huge international collaborations with openness as a key principle. Thousands of people in hundreds of labs have worked on generating the various versions of human and other species's genomes over the past few years; last week, the ancient fish the coelacanth became the latest to join the genome club. All the data is in the public domain, to maximise the benefit for as many people as possible. Our control of the stuff of life is such that we can now eschew DNA's evolved functions altogether. In its simplest form, DNA is an information storage format. It is incredibly stable: we have extracted meaningful DNA from all sorts of long-dead organisms, including mammoths and Neanderthals.

People started thinking about DNA as a data storage device in the 1990s, but it wasn't until 2010 that scientist Craig Venter hid several secret coded messages in the DNA of his synthetic cell, nicknamed Synthia . This field really kicked off in January when a team led by Cambridge geneticist Ewan Birney encoded in DNA all Shakespeare's sonnets, a video of Martin Luther King's "I have a dream" speech, and Crick and Watson's 1953 paper. They sent it to a lab in Germany, where it was decrypted with an error rate of zero. Currently, this technique is only useful for archiving, because it is slow to write and decode, but the density of information is higher than for Blu-Ray discs or hard drives. We will never not study DNA, so the technology for reading and writing it will only improve. Remember Betamax or laser discs? DNA is a format that has robustly stored data for 4bn years. While the principles of how living DNA encodes information and duplicates are set in stone, this is no longer true for the molecule itself. In the past few years we have seen startling progress towards reinventing the language of life.

That original four-letter alphabet is now up to at least six, with the addition of Z and P by scientists including Steve Benner at the Foundation for Applied Molecular Evolution in Florida. These new letters don't mean anything yet: it is as if we had added letters to English that could not yet be pronounced. But Benner has incorporated them into a molecule whose alphabet has remained frozen for several billion years. Last year a team in Cambridge led by Vitor Pinheiro re-engineered the struts of the double helix ladder , changing the D in DNA to a host of other molecules, under the catch-all title of "XNA". They reproduce, evolve, and have the potential to act as therapeutic drugs, because the body won't recognise them as rogue DNA. Sixty years on from the first revelation of DNA's shapely curves, no aspect of biology is above modification, remix or redesign. This inevitably comes with accusations of " playing God ". Yet this is what we have always done. We have taken the natural world, modified it, shaped it and redesigned it to suit our own needs and wants, often without considering the repercussions. All of these new endeavours are fraught with contention. Gene patenting is one perhaps soon to be resolved.

Ownership of GM seeds by corporate monoliths continues to provoke ire from many. There is a visceral belief in some quarters that we shouldn't be fiddling with nature in such fundamental ways. Nevertheless, DNA technology will continue to grow. But it is our responsibility to allow DNA technology to flourish, while society makes informed decisions about how its fruits are shared. We are in a golden age, an industrial revolution with a single root exactly six decades ago. BBC NEWS | Science/Nature | 'Secret of life' discovery turns 50 'Secret of life' discovery turns 50 By Ivan Noble BBC News Online science staff It was simple; instantly you could explain this idea to anyone Professor James Watson Fifty years ago, on 28 February 1953, Francis Crick walked into the Eagle pub in Cambridge, UK, and announced something for which he would later share a Nobel Prize. "We have found the secret of life," his collaborator and subsequent fellow Nobel laureate James Watson later quoted him as saying. The pair really had figured out something very close to that. Working out the famous double helix structure of DNA was an achievement which led to countless advances and solved a mystery which had troubled scientists for decades.

"When we saw the answer we had to pinch ourselves," Watson told the BBC in an anniversary interview. "Could it really be this pretty? When we went to lunch [at the Eagle] we realised it probably was true because it was so pretty." Simple recipe During World War II, researchers had shown that the mysterious substance which carries genes from generation to generation was DNA. THE DNA MOLECULE The double-stranded DNA molecule is held together by chemical components called bases Adenine (A) bonds with thymine (T); cytosine(C) bonds with guanine (G) Groupings of these letters form the "code of life"; there are about 2.9 billion base pairs in the human genome wound into 24 distinct bundles, or chromosomes Written in the DNA are 30,000-40,000 genes which human cells use as templates to make proteins; these sophisticated molecules build and maintain our bodies But knowing that DNA was the wonder molecule did not tell them how it did its job or what it looked like. Before Watson and Crick made their breakthrough, scientists knew that the DNA molecule was made of a few relatively simple chemicals.

They had the recipe for DNA, but no-one was sure how these simple chemicals combined to carry the huge amount of information required to recreate a living thing. Instead of carrying out experiments, Watson and Crick set out to think their way out of the problem. Other researchers had come up with possible models of the structure of DNA, but they were flawed. Watson and Crick came up with their own after calculating what they thought it should look like. They could not be sure about their model, though, until they had a stroke of luck. X-ray image key A team at King's College in London had for several years been doing experiments using the relatively new technique of X-ray crystallography. One of them, Rosalind Franklin, had taken a now famous image of the X-ray diffraction pattern from crystalline DNA showing a clear cross shape. Franklin's colleague, Maurice Wilkins, let Watson see the image during a visit to London but did not tell her. Watson and Crick had already worked out what the X-ray photo of DNA should look like if their model was correct. When Watson saw Franklin's image, he knew that he and Crick were right. And so to 28 February 1953.

"The discovery was made on that day, not slowly over the course of the week," James Watson said. "It was simple; instantly you could explain this idea to anyone - you didn't have to be a high powered scientist to see how the genetic material was copied." The pair published their famous paper in Nature on 25 April that year, revealing to the world the double helix and hinting how the fact that DNA has two strands allows it to create identical copies of itself. Billions of units The idea took a while to attract attention, but over the decades that have since passed it became the basis for many of the famous achievements of modern biology and medicine. Watson, Crick and Wilkins shared a Nobel Prize for their work, but Franklin died in her 30s of cancer, still unaware of the decisive role of her image. The double helix: A modern icon Nobel Prize rules do not allow for posthumous awards. Watson said she would probably have got to the structure herself if he and Crick had not got there in the February. "If Rosalind had continued to think about DNA - she was giving it up - [she could have found the answer].

"Unknown to us at just about the time we found it, she had concluded that [DNA] was a two-chain helix. But she hadn't thought of how you would put the bases in the centre. But it would have been hard for her not to ask how you put the bases in the centre." Watson went on to be closely involved with the Human Genome Project, which set out to decipher the meaning of the billions of units of genetic information contained in human DNA. Discovery of DNA Structure and Function: Watson and Crick | Learn Science at Scitable Discovery of DNA Structure and Function: Watson and Crick By: Leslie A. Pray, Ph.D. © 2008 Nature Education Citation: Pray, L. (2008) Discovery of DNA structure and function: Watson and Crick. Nature Education 1(1):100 The landmark ideas of Watson and Crick relied heavily on the work of other scientists. What did the duo actually discover? Many people believe that American biologist James Watson and English physicist Francis Crick discovered DNA in the 1950s. In reality, this is not the case.

Rather, DNA was first identified in the late 1860s by Swiss chemist Friedrich Miescher. Then, in the decades following Miescher's discovery, other scientists--notably, Phoebus Levene and Erwin Chargaff--carried out a series of research efforts that revealed additional details about the DNA molecule, including its primary chemical components and the ways in which they joined with one another. Without the scientific foundation provided by these pioneers, Watson and Crick may never have reached their groundbreaking conclusion of 1953: that the DNA molecule exists in the form of a three-dimensional double helix. The First Piece of the Puzzle: Miescher Discovers DNA Although few people realize it, 1869 was a landmark year in genetic research, because it was the year in which Swiss physiological chemist Friedrich Miescher first identified what he called "nuclein" inside the nuclei of human white blood cells.

(The term "nuclein" was later changed to "nucleic acid" and eventually to "deoxyribonucleic acid," or "DNA.") Miescher's plan was to isolate and characterize not the nuclein (which nobody at that time realized existed) but instead the protein components of leukocytes (white blood cells). Miescher thus made arrangements for a local surgical clinic to send him used, pus-coated patient bandages; once he received the bandages, he planned to wash them, filter out the leukocytes, and extract and identify the various proteins within the white blood cells. But when he came across a substance from the cell nuclei that had chemical properties unlike any protein, including a much higher phosphorous content and resistance to proteolysis (protein digestion), Miescher realized that he had discovered a new substance (Dahm, 2008). Sensing the importance of his findings, Miescher wrote, "It seems probable to me that a whole family of such slightly varying phosphorous-containing substances will appear, as a group of nucleins, equivalent to proteins" (Wolf, 2003).

More than 50 years passed before the significance of Miescher's discovery of nucleic acids was widely appreciated by the scientific community. For instance, in a 1971 essay on the history of nucleic acid research, Erwin Chargaff noted that in a 1961 historical account of nineteenth-century science, Charles Darwin was mentioned 31 times, Thomas Huxley 14 times, but Miescher not even once. This omission is all the more remarkable given that, as Chargaff also noted, Miescher's discovery of nucleic acids was unique among the discoveries of the four major cellular components (i.e., proteins, lipids, polysaccharides, and nucleic acids) in that it could be "dated precisely... [to] one man, one place, one date." Laying the Groundwork: Levene Investigates the Structure of DNA Meanwhile, even as Miescher's name fell into obscurity by the twentieth century, other scientists continued to investigate the chemical nature of the molecule formerly known as nuclein. One of these other scientists was Russian biochemist Phoebus Levene.

A physician turned chemist, Levene was a prolific researcher, publishing more than 700 papers on the chemistry of biological molecules over the course of his career. Levene is credited with many firsts. For instance, he was the first to discover the order of the three major components of a single nucleotide (phosphate-sugar-base); the first to discover the carbohydrate component of RNA (ribose); the first to discover the carbohydrate component of DNA (deoxyribose); and the first to correctly identify the way RNA and DNA molecules are put together. During the early years of Levene's career, neither Levene nor any other scientist of the time knew how the individual nucleotide components of DNA were arranged in space; discovery of the sugar-phosphate backbone of the DNA molecule was still years away. The large number of molecular groups made available for binding by each nucleotide component meant that there were numerous alternate ways that the components could combine. Several scientists put forth suggestions for how this might occur, but it was Levene's "polynucleotide" model that proved to be the correct one.

Based upon years of work using hydrolysis to break down and analyze yeast nucleic acids, Levene proposed that nucleic acids were composed of a series of nucleotides, and that each nucleotide was in turn composed of just one of four nitrogen-containing bases, a sugar molecule, and a phosphate group. Levene made his initial proposal in 1919, discrediting other suggestions that had been put forth about the structure of nucleic acids. In Levene's own words, "New facts and new evidence may cause its alteration, but there is no doubt as to the polynucleotide structure of the yeast nucleic acid" (1919). Indeed, many new facts and much new evidence soon emerged and caused alterations to Levene's proposal. One key discovery during this period involved the way in which nucleotides are ordered. Levene proposed what he called a tetranucleotide structure, in which the nucleotides were always linked in the same order (i.e., G-C-T-A-G-C-T-A and so on).

However, scientists eventually realized that Levene's proposed tetranucleotide structure was overly simplistic and that the order of nucleotides along a stretch of DNA (or RNA) is, in fact, highly variable. Despite this realization, Levene's proposed polynucleotide structure was accurate in many regards. For example, we now know that DNA is in fact composed of a series of nucleotides and that each nucleotide has three components: a phosphate group; either a ribose (in the case of RNA) or a deoxyribose (in the case of DNA) sugar; and a single nitrogen-containing base. We also know that there are two basic categories of nitrogenous bases: the purines (adenine [A] and guanine [G]), each with two fused rings, and the pyrimidines (cytosine [C], thymine [T], and uracil [U]), each with a single ring. Furthermore, it is now widely accepted that RNA contains only A, G, C, and U (no T), whereas DNA contains only A, G, C, and T (no U) (Figure 1). Figure 1: The chemical structure of a nucleotide.

A single nucleotide is made up of three components: a nitrogen-containing base, a five-carbon sugar, and a phosphate group. The nitrogenous base is either a purine or a pyrimidine. The five-carbon sugar is either a ribose (in RNA) or a deoxyribose (in DNA) molecule. James Watson :: DNA from the Beginning Maurice Wilkins (1916-2004) James Watson (1928-) James Dewey Watson was born in Chicago. As a child, he was bright and inquisitive. One of his favorite words was "why?" and he wasn't satisfied with simple answers. He accumulated a lot of knowledge by reading the World Almanac, and won $100 as a "Quiz Kid" on a popular radio program. He used this money to buy binoculars for bird-watching ? a serious hobby for himself and his father. Watson entered the University of Chicago at 15 under the gifted youngster program. He did well in courses that interested him, like biology and zoology, and not as well in other courses.

He decided that he would go to graduate school and study to become the curator of ornithology at the Museum of Natural History . In his senior year at Chicago, Watson read Erwin Schrödinger's book: What is Life? The Physical Aspect of the Living Cell. He was fascinated by the idea that genes and chromosomes hold the secrets of life. When Watson went to do a Ph.D. with Salvador Luria , a pioneer in bacteriophage research, at Indiana University , it seemed the perfect opportunity to work on some of these problems. After his Ph.D. in 1950, Watson spent time in Europe, first in Copenhagen and then at the Cavendish Laboratory of the University of Cambridge . By now, Watson knew that DNA was the key to understanding life and he was determined to solve its structure. He was lucky to share an office with Francis Crick , a Ph.D. student who was also interested in the structure of DNA. Although both were supposed to be working on other projects, in 1953, they built the first accurate model of DNA ? one of the great scientific advances of all time.

In 1962, Watson shared the Nobel Prize for Physiology or Medicine with Francis Crick and Maurice Wilkins who, with Rosalind Franklin, provided the data on which the structure was based. Watson wrote The Double Helix: A Personal Account of the Discovery of the Structure of DNA, which was published in 1968. This book was the first of its kind, being a gossipy account of the inner workings of the scientific world, and has never been out of print. In 1956, Watson accepted a position in the Biology department at Harvard University where the focus of his research was RNA and its role in the transfer of genetic information. Although he continued to be a member of the Harvard faculty until 1976, Watson took over the directorship of Cold Spring Harbor Laboratory in 1968. Watson has had a long association with Cold Spring Harbor Lab. Salvador Luria and Max Delbrück taught a popular summer course on phage genetics, and during his graduate days, Watson enjoyed this "summer camp" for scientists. Watson has made Cold Spring Harbor Laboratory one of the world's premier research facilities for cancer, neurobiology, and basic molecular genetics.

Watson retired as the President of Cold Spring Harbor Laboratory in 2004, and is now Chancellor Emeritus . Watson has played a significant role in the development of science policy, from the War on Cancer, through the debates over the use of recombinant DNA, to promoting the Human Genome Project. From 1988 to 1992, he ran the Human Genome Project at the National Institutes of Health while still directing Cold Spring Harbor Laboratory. One of his major interests is education. His first textbook, Molecular Biology of the Gene, set new standards for biology textbooks, and it was followed by Molecular Biology of the Cell, and Recombinant DNA. He is actively exploring the avenue of multimedia education and the WWW through projects being developed at the DNA Learning Center , the educational arm of Cold Spring Harbor Laboratory. He was and is one of the main motivators of this project, DNA from the Beginning. Watson has been described by many as brilliant, outspoken and eccentric. He is energized by intelligent people and doesn't suffer fools. Watson is an avid tennis player and has been ever since his grad school days. He still tries to play tennis every day.

DNA was first crystallized in the late 70's — remember, the 1953 X-ray data were from DNA fibers. So, the real "proof" for the Watson-Crick model of DNA came in 1982 after the B-form of DNA was crystallized and the X-ray pattern was solved. If the DNA of one human cell is stretched out, it would be almost 6 feet long and contain over three billion base pairs. How does all this fit into the nucleus of one cell?

Question: Watson and Crick discovered DNA in what year?
Answer: 1953