Cristalografia2

81
-1

Published on

Published in: Technology
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
81
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
2
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Cristalografia2

  1. 1. Cristalografía ************************************************** ************************************************** Cristalografía Wikipedia (20130330) “La cristalografía es la ciencia que se dedica al estudio y resolución de estructuras cristalinas. La mayoría de los minerales adoptan formas cristalinas cuando se forman en condiciones favorables. La cristalografía es el estudio del crecimiento, la forma y la geometría de estos cristales.” http://es.wikipedia.org/wiki/Cristalograf%C3%ADa “Elementos de simetría Las celdas fundamentales de un cristal presentan elementos de simetría, que son: • Eje de simetría: es una línea imaginaria que pasa a través del cristal, alrededor de la cual, al realizar éste un giro completo, repite dos o más veces el mismo aspecto. Los ejes pueden ser: monarios, si giran el motivo una vez (360º); binarios, si lo giran dos veces (180º); ternarios, si lo giran tres veces (120º); cuaternarios, si lo giran cuatro veces (90º); o senarios, si giran el motivo seis veces (60º). • Plano de simetría: es un plano imaginario que divide el cristal en dos mitades simétricas especulares, como el reflejo en un espejo, dentro de la celda. Puede haber múltiples planos de simetría. Se representa con la letra m. • Centro de simetría: es un punto dentro de la celda que, al unirlo con cualquiera de la superficie, repite al otro lado del centro y a la misma distancia un punto similar. • Sistemas cristalinos: todas la redes cristalinas, al igual que los cristales, que son una consecuencia de las redes, presentan elementos de simetría. Si se clasifican los 230 grupos espaciales según los elementos de simetría que poseen, se obtienen 32 clases de simetría (cada una de las cuales reúne todas las formas cristalinas que poseen los mismos elementos de simetría) es decir, regular o cúbico, tetragonal, hexagonal, romboédrico, rómbico, monoclínico y triclínico. http://es.wikipedia.org/wiki/Cristalograf%C3%ADa#Elementos_de_simetr.C3.ADa ************************************************** “and was openly discussed by Franklin in lectures attended by Watson and in reports accessible to Watson and Crick, that DNA (1) was helical, (2) was likely a double helix with antiparallel strands, and, (3) had the phosphate backbone on the outside (thus the bases of DNA, which are the "code" for inheritance, were on the inside of the helix). Calculations from the photograph also provided crucial parameters for the size of the helix and its structure, all of which were critical for the molecular modeling undertaken by Watson and Crick.” Rosalind Franklin Photo_51 Wikipedia (20130330)
  2. 2. http://en.wikipedia.org/wiki/Photo_51 Rosalind Franklin Rosalind E. Franklin http://en.wikipedia.org/wiki/File:Rosalind_Franklin.jpg Rosalind Elsie Franklin (25 July 1920 – 16 April 1958)[1] was a British biophysicist and X-ray crystallographer who made critical contributions to the understanding of the fine molecular structures of DNA, RNA, viruses, coal, and graphite.[2] Her DNA work achieved the most fame because DNA (deoxyribonucleic acid) plays essential roles in cell metabolism and genetics, and the discovery of its structure helped scientists understand how genetic information is passed from parents to children. Franklin is best known for her work on the X-ray diffraction images of DNA which led to the discovery of DNA double helix. Her data, according to Francis Crick, were "the data we actually used"[3] to formulate Crick and Watson's 1953 hypothesis regarding the structure of DNA.[4] Franklin's images of X-ray diffraction confirming the helical structure of DNA were shown to Watson without her approval or knowledge. Though this image and her accurate interpretation of the data provided valuable insight into the DNA structure, Franklin's scientific contributions to the discovery of the double helix are often overlooked[citation needed] . Unpublished drafts of her papers (written just as she was arranging to leave King's College London) show that she had independently determined the overall B- form of the DNA helix and the location of the phosphate groups on the outside of the structure. Moreover, Franklin personally told Crick and Watson that the backbones had to be on the outside, which was crucial since before this both they and Linus Pauling had independently generated non-illuminating models with the chains inside and the bases pointing outwards.[5] However, her work was published third, in the series of three DNA Nature articles, led by the paper of Watson and Crick which only hinted at her contribution to their hypothesis.[6] Rosalind Franklin Wikipedia (20130330) “Rosalind Elsie Franklin (25 de julio de 1920 en Kensington, Londres – 16 de abril de 1958 en Chelsea, Londres) fue una biofísica y cristalógrafa inglesa autora de importantes
  3. 3. contribuciones a la comprensión de las estructuras del ADN, los virus, el carbón y el grafito. A Franklin se la recuerda principalmente por la llamada Fotografía 51, la imagen del ADN obtenida mediante difracción de rayos X, que sirvió como fundamento para la hipótesis de la estructura doble helicoidal del ADN en la publicación del artículo de James Watson y Francis Crick de 1953,1 y tras su publicación constituyó una prueba crítica para la hipótesis.” http://es.wikipedia.org/wiki/Rosalind_Franklin Rosalind Franklin La investigación sobre el ADN Wikipedia (20130330) “En 1951, regresó a Inglaterra para trabajar como investigadora asociada en el laboratorio de John Randall en el King's College de Londres. Rosalind Franklin, una mujer de personalidad fuerte, mantuvo aquí una relación compleja con Maurice Wilkins, quien mostró sin su permiso sus imágenes de difracción de rayos X del ADN a James Watson y Francis Crick. Ninguna otra inspiración fue tan fuerte como ésta para la publicación por ellos, en 1953, de la estructura del ADN, tal como ellos mismos reconocieron. En febrero de 1953, a la edad de 33 años, Rosalind escribió en sus notas de trabajo "la estructura del ADN tiene dos cadenas". Para ese entonces, ella también sabía que la molécula del ADN tiene sus grupos fosfato hacia afuera y que existe en dos formas” http://es.wikipedia.org/wiki/Rosalind_Franklin#La_investigaci.C3.B3n_sobre_el_ADN Photo 51 Wikipedia (20130330) Photo 51, showing DNA structure “Photo 51 is the nickname given to an X-ray diffraction image of DNA taken by Rosalind Franklin in May 1952,[1][2][3] when she was working at King's College London in Sir John Randall's group. It was critical evidence[4] in identifying the structure of DNA.[5]
  4. 4. James D. Watson was shown the photo by Maurice Wilkins, who had been given it by Raymond Gosling; along with Francis Crick, he used Photo 51 to develop the first chemical model of DNA, for which the three men jointly won the 1962 Nobel Prize in Physiology or Medicine. As the Nobel prize is not awarded posthumously, Franklin, who had died in 1958, was not eligible for nomination.[6] The photograph provided key information that was essential for developing a model of B- form (hydrated) DNA.[7][8] In particular, it could be determined from the diffraction pattern, and was openly discussed by Franklin in lectures attended by Watson and in reports accessible to Watson and Crick, that DNA (1) was helical, (2) was likely a double helix with antiparallel strands, and, (3) had the phosphate backbone on the outside (thus the bases of DNA, which are the "code" for inheritance, were on the inside of the helix). Calculations from the photograph also provided crucial parameters for the size of the helix and its structure, all of which were critical for the molecular modeling undertaken by Watson and Crick.[7][9][10] Photo 51 was, therefore, the critical data[11] that led to the model and confirmation of the postulated double helical structure of DNA, published during 1953 in a series of five articles in the journal Nature.[12] Franklin and Raymond Gosling's own publication in the same issue of Nature was the first publication of this more clarified X-ray image of DNA” http://en.wikipedia.org/wiki/Photo_51 Fotografía 51 Wikipedia (20130330) “Fotografía 51 es el nombre dado a una imagen del ADN obtenida por Rosalind Franklin mediante difracción de rayos X en 1952,1 y que fue una evidencia fundamental,2 para identificar la estructura del ADN.3 La fotografía fue tomada por Franklin mientras trabajaba en el King's College London, en el grupo de Sir John Randall.” http://es.wikipedia.org/wiki/Fotograf%C3%ADa_51 Franklin R, Gosling RG (1953) "Molecular Configuration in Sodium Thymonucleate". Nature 171: 740–741., April 25, 1953 http://www.nature.com/nature/dna50/franklingosling.pdf Original papers - franklingosling.pdf Photo 51, showing DNA structure http://en.wikipedia.org/wiki/File:Photo_51_x-ray_diffraction_image.jpg ************************************************** **************************************************

×