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She then studied natural sciences at Newnham College, Cambridge , from which she graduated in Earning a research fellowship, she joined the University of Cambridge physical chemistry laboratory under Ronald George Wreyford Norrish , who disappointed her for his lack of enthusiasm. This helped her earn a Ph.
Rosalind Franklin and DNA
Skip navigation. Franklin took Photo 51 after scientists confirmed that DNA contained genes. Watson and Crick used that image to develop their structural model of DNA. X-ray crystallography, the technique Franklin used to produce Photo 51 of DNA, is a method scientists use to determine the three-dimensional structure of a crystal. Crystals are solids with regular, repeating units of atoms. Some biological macromolecules, such as DNA, can form fibers suitable for analysis using X-ray crystallography because their solid forms consist of atoms arranged in a regular pattern.
To perform an X-ray crystallography, scientists mount a purified fiber or crystal in an X-ray tube. The X-ray tube generates X-rays that strike the purified material.
X-rays are electromagnetic waves that have a shorter wavelength and higher energy than visible light. Because of their short wavelength, X-rays can pass through a crystal and interact with the electrons of the atoms within the crystal.
When X-rays interact with electrons in a crystal the X-rays scatter, or diffract, at angles that indicate the arrangement of atoms in the crystal, or its structure. When the X-rays scatter, they strike a film mounted behind the crystal and leave a pattern of dark marks. The pattern of dark marks on the film gives scientists information about the structure of the crystal. However, at that time scientists generally agreed that DNA merely provided structural support for cells and that protein must be genetic material.
When mounting the DNA fibers for viewing, Wilkins and Gosling were able to bundle many of the thin fibers together and pull them tight to provide a larger sample to better diffract X-rays. Furthermore, the two researchers kept the DNA fibers wet with water by keeping them in a humid environment. The resulting X-ray diffraction pattern of DNA was of a higher quality than any patterns collected prior. Before joining the lab, Franklin conducted X-ray diffraction experiments on carbon compounds at a government lab in Paris, France, and published several papers on X-ray crystallography of coal and coal compounds.
By improving her methods of collecting DNA X-ray diffraction images, Franklin obtained Photo 51 from an X-ray crystallography experiment she conducted on 6 May First, she minimized how much the X-rays scattered off the air surrounding the crystal by pumping hydrogen gas around the crystal. Because hydrogen only has one electron, it does not scatter X-rays well. She pumped hydrogen gas through a salt solution to maintain the targeted hydration of the DNA fibers.
Franklin tuned the salt concentration of the solution and the humidity surrounding the crystal to keep DNA entirely in the B-Form. After exposing the DNA fibers to X-rays for a total of sixty-two hours, Franklin collected the resulting diffraction pattern and labeled it Number 51 that became Photo The outermost edge of the diffraction pattern consists of a black diamond shape.
The diamond has rounded corners with the darkest corners situated at the top and bottom of the film. The diamond shape of the DNA diffraction pattern is not made of fine, definite lines, but rather thick, fuzzy boarders that vary in darkness such that the boarders fade on the left and right hand sides of the film.
Inside the diamond is a cross shape like the letter "X. Instead, along each line of the X are four horizontal dashes, called spots that become darker moving closer to the center of the film. There is a hole at the center of the film, with dark spots lining the outside of the center hole. Each nucleotide has three key features. Each nucleotide consists of a center sugar ring called deoxyribose. Attached to one end of the deoxyribose ring is a negatively charged phosphate group consisting of phosphorus and oxygen atoms.
Attached to the other end of the deoxyribose ring is a molecule called a base consisting of either single or double rings of carbon and nitrogen.
There are four types of bases in DNA. The presence of the X shape in the diffraction pattern indicated to Franklin that DNA strands were helical. Each dash of the X shape marks the repetition of atoms, or atomic repeats, in DNA. Therefore, based on the distances between the dashes, Franklin determined the distance between nucleotides, the smallest repeating units in DNA. The angles of the X shape revealed to Franklin the radius of DNA, or half the horizontal distance from one side of the molecule to the other.
From the distance between the top and bottom of the outer diamond shape, Franklin found that there are ten nucleotides between each turn of the DNA molecule. Lastly, the lighter nature of the diamond on the top and bottom of the film showed Franklin that the DNA bases face the inside of the helix whereas the phosphate groups face outside.
While Franklin obtained Photo 51 in May , she did not complete her analysis of Photo 51 until early From the image, Watson concluded that DNA was helical. From that report, Crick determined that DNA contains two strands, with each strand running in opposite directions.
The model they suggested consisted of two helical strands of repeating nucleotides wound around each other making a double helix. The double helix had ten nucleotides between each turn. The phosphate groups faced outside the double helix and the DNA bases faced horizontally inward of the helix.
The two strands held together through interactions between the bases of each strand. The DNA strands ran in opposite directions.
Their replication mechanism, later called semi-conservative replication, described how to copy the DNA molecule that contained the genes and to pass the genes from cell to cell and from parent to offspring. Watson and Crick proposed that the DNA strands needed to unwind and separate in order to replicate. However, because of the helical nature of DNA, as shown in the X-ray diffraction pattern of Photo 51, some scientists argued that the DNA strands would be too difficult to unwind and separate.
Some years passed before scientists accepted semi-conservative replication due to the perceived difficulty of unwinding the helical strands. Franklin also contributed to understanding DNA structure, especially through her collection of Photo The award of the Nobel Prize is never posthumously and Franklin died in before the award of the Nobel Prize.
The DNA structure revealed in Photo 51 related the essential functions of a gene how its information is preserved and carried from cells to cell and from parent to offspring.
Franklin, Rosalind E. Hamilton, Leonard D. The Eighth Day of Creation. Klug, Aaron. Lucas, Amand A. Lucas, Amand. Maddox, Brenda.
London: HarperCollins Publishers, Marsh, Richard E. Sayre, Anne. Rosalind Franklin and DNA. New York: W. Watson, James D. New York: Athenaeum Press, Printer-friendly version PDF version.
the double helix analysis
Clyde Manwell, C. Carl Leopold's July BioScience — postulate that certain aspects of the social structure of science inhibit creativity is tested by analysis of the various views of the path to the discovery of the double helical structure of DNA. Cognitive dissonance can result in serious distortions in science, including suppression of dissident scientists by personal calumny. Most users should sign in with their email address. If you originally registered with a username please use that to sign in.
PDF | On Nov 28, , Evelyn Fox Keller published Watson's Needle: Rosalind Franklin and DNA, by Anne Sayre | Find, read and cite all the.
Photograph 51, by Rosalind Franklin (1952)
The script was written by William Nicholson, and it was produced and directed by Mick Jackson. They barely communicated, and Franklin by herself made slow progress, opening up the strong possibility that the American chemist Linus Pauling would solve the problem first. Watson had very limited contact with Franklin during the time she worked on DNA. This naturally set up a poisonous state of affairs between Franklin and Wilkins. As he later pursued a PhD in biochemistry, he realized, evolutionary decisions?
Published by Norton in New York. Written in English. This book is well-written, it provides a very personal and moving perspective of Rosalind Franklin's life.
Похоже, в них угадывался страх. Или это ненависть. Они буквально пожирали ее тело. Новая волна паники охватила Сьюзан. Хейл всей тяжестью своего тела придавил ее ноги, холодно следя за каждым ее движением.
Какого черта! - подумал. - Что я делаю здесь в пять вечера в субботу. - Чед? - В дверях его кабинета возникла Мидж Милкен, эксперт внутренней безопасности Фонтейна. В свои шестьдесят она была немного тяжеловатой, но все еще весьма привлекательной женщиной, чем не переставала изумлять Бринкерхоффа. Кокетка до мозга костей, трижды разведенная, Мидж двигалась по шестикомнатным директорским апартаментам с вызывающей самоуверенностью.
Как старшему криптографу ей полагался терминал с самым лучшим обзором. Он был установлен на задней стороне компьютерного кольца и обращен в сторону шифровалки. Со своего места Сьюзан могла видеть всю комнату, а также сквозь стекло одностороннего обзора ТРАНСТЕКСТ, возвышавшийся в самом центре шифровалки.
Он знал, что Фонтейн прав: у них нет иного выбора. Время на исходе. Джабба сел за монитор. - Хорошо. Давайте попробуем.
Стратмор провел рукой по вспотевшему лбу. - Этот шифр есть продукт нового типа шифровального алгоритма, с таким нам еще не приходилось сталкиваться. Эти слова повергли Сьюзан в еще большее смятение. Шифровальный алгоритм - это просто набор математических формул для преобразования текста в шифр.
Их прикосновение было знакомым, но вызывало отвращение. Б нем не чувствовалось грубой силы Грега Хейла, скорее - жестокость отчаяния, внутренняя бездушная решительность. Сьюзан повернулась.
Алчущие хакеры прорывались со всех уголков мира. Их количество удваивалось каждую минуту. Еще немного, и любой обладатель компьютера - иностранные шпионы, радикалы, террористы - получит доступ в хранилище секретной информации американского правительства. Пока техники тщетно старались отключить электропитание, собравшиеся на подиуме пытались понять расшифрованный текст. Дэвид Беккер и два оперативных агента тоже пробовали сделать это, сидя в мини-автобусе в Севилье.