Crystals To Diffract X Rays example essay topic

Who is Rosalind Franklin Born on July 25, 1920 in London, England, Rosalind Elise Franklin was a catalyst to many other scientists in the field of genetics. Using coal and carbon as subjects, Franklin discovered the double helix of DNA, the shape that two linear strands of DNA assume when bonded together. In 1945, Franklin received her Ph. D in physical chemistry from Cambridge University. The next year she went to Paris and worked in the Laboratoire Central des Services Chi miques de LEt at until 1950 where she concentrated her studies on x-ray diffraction methods. In 1951, Franklin returned to England to work as an associate to John Randall at Kings College. While Maurice Wilkins, a scientist, was away, Franklin was put in charge of his DNA project.

Wilkins returned to think that Franklin was a lowly technical assistant mainly because of the discrimination against women at that time. During her studies, Franklin took pictures of the DNA structure using her own technique discovering a helical structure. Through this technique, Franklin discovered that there were two types of DNA, dry A-form and wet b-form. B-form being the DNA that exist within our bodies.

She also located the position of phosphate sugars in DNA. With this technique, the locations of atoms can be precisely mapped by looking at the crystal under an x-ray beam. How X-Rays work Unfortunately, unlike with visible light, there is no known way to focus x-rays with a lens. This causes an x-ray microscope to be impossible to use unless someone finds a way of focusing x-rays. So it is necessary to use crystals to diffract x-rays and create a diffraction pattern. Crystals are important because by definition they have a repeated unit cell within them.

The x-ray diffraction from one unit cell would not be significant. Fortunately, the repetition of unit cells within a crystal amplifies the diffraction enough to give results that ca turn into a picture. To perform x-ray crystallography, it is necessary to grow crystals with edges around 0.1-0.3 mm. Crystals are formed as the conditions in a supersaturated solution slowly change. There are three degrees of saturation in solution, and crystallographers take advantage of these when growing crystals: Unsaturated - where no crystals will form or grow.

Low supersaturated - where crystals will grow but no new ones will form. High supersaturated - where crystals will both form and grow. Back to her life Between 1951 and 1953, Franklin came close to discovering the structure of DNA but was sabotaged by James Watson and Francis Crick, an American Biochemist and British Biochemist, respectively. Without Franklins knowledge or permission, the two published all her information and some of her pictures.

Among these pictures was one of Franklins crystallographic photos of DNA. She later published the same information in a science journal and published five other articles. Four years after her death Crick and Francis were awarded the Nobel Prize for the Double Helix model of DNA. During this time in the laboratory, Franklin produced clear pictures of the helix that are still used in textbooks today. In the spring of 1953, Franklin moved to J. D Beroznals laboratory at Birkbeck College. She worked on the tobacco mosaic virus and the polio virus.

During this time she was asked to speak at many conferences around the world and published 17 papers in five years. Her research laid a foundation for structural virology. In the summer of 1956, Franklin became sick and was diagnosed by an American doctor with ovarian cancer. She continued work over the next two years through three operations, experimental chemotherapy and a 10-month remission. She worked up to a few weeks before her death on April 16, 1958 in London at age 37. After her death, Anne Sayre, a friend, wrote the book Rosalind Franklin and DNA that told the real story of Franklins role in DNA research.

This book was published in 1975. Because of this book, Franklin finally received recognition for her discoveries. Sir Aaron Klug, 1982 Nobel Laureate in Chemistry stated that Rosalind Franklin made crucial contributions to the solution of the structure of DNA. She discovered the B form, recognized that two states of the DNA molecule existed and defined conditions for the transition.

From early on, she realized that any correct model must have the phosphate groups on the outside of the molecule. She laid the basis for the quantitative study of the diffraction patterns, and after the formation of the Watson - Crick model she demonstrated that a double helix was consistent with the X-ray patterns of both the A and B forms. Sir Aaron Klug is known for his development of crystallographic electron microscopy and his structural elucidation of biologically important nuclei acid-protein complexes.