Rosetta Stone of the genetic language

Lucas, A. A.

doi:10.1002/qua.10351

Cited by 6 publications

(8 citation statements)

References 15 publications

(22 reference statements)

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“…The angle of the lines of the X shape (about 40° in Figure 7) equals the angle between the zigzagging, edge on base pairs in A-DNA. In addition, the intensity of the X shape is weak along the lower-order layer lines (3-5) and strong along the higher-order layer lines (6)(7)(8). The reason for this is that the intensity of the X shape is modulated by the envelope of the Thomas Young diffraction of each double slit.…”

Section: Optical Simulationsmentioning

confidence: 99%

A-DNA and B-DNA: Comparing Their Historical X-ray Fiber Diffraction Images

Lucas¹

2008

J. Chem. Educ.

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A-DNA and B-DNA are two secondary molecular conformations (among other allomorphs) that double-stranded DNA drawn into a fiber can assume, depending on the relative water content and other chemical parameters of the fiber. They were the first two forms to be observed by X-ray fiber diffraction in the early 1950s, respectively by Wilkins and Gosling and by Franklin and Gosling. Their corresponding historical diffraction diagrams played an equally crucial role in the discovery of the primary double-helical structure of the DNA molecule by Watson and Crick in 1953. This paper provides a comparative explanation of the structural content of the two diagrams treated on the same footing. The analysis of the diagrams is supported by the optical transform method with which both A-DNA and B-DNA X-ray images can be simulated optically. The simulations use a simple laser pointer and a dozen optical diffraction gratings, all held on a single diffraction slide. The gratings have been specially designed to pinpoint just which of the structural elements of the molecule is responsible for each of the revealing features of the fiber diffraction images.

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Section: Optical Simulationsmentioning

confidence: 99%

A-DNA and B-DNA: Comparing Their Historical X-ray Fiber Diffraction Images

Lucas¹

2008

J. Chem. Educ.

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“…On the other hand, from the same argument, one might expect a nonzero intensity on the meridian of the l = 9 layer-line where x ≈ 3.5, but this happens to be close to the first zero of J 1 (x) at x = 3.8; so, fortuitously, there is no or very weak intensity there for the particular parameters of the phosphorus helix illustrated in figure 6(b). The diffraction pattern is quite sensitive not only to the helix parameters but also to the angular orientation of the atomic helix around its axis [32]. In the numerical simulation of figure 6(b), the intensities have been averaged over the helix angular orientation (as in a gel fibre).…”

Section: Atomic Helixmentioning

confidence: 99%

“…In the simulation of figure 6(c), the layer-lines are projected from the centre of the Ewald sphere corresponding to Cu K α x-rays and indeed they do appear hyperbolic and chirped, as in the real x-ray patterns. A more detailed discussion of the CCV analytical formulae can be found in the original CCV paper [23] and in [32].…”

Section: Atomic Helixmentioning

confidence: 99%

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Diffraction by DNA, carbon nanotubes and other helical nanostructures

Lucas

Lambin

2005

Rep. Prog. Phys.

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This review discusses the diffraction patterns of x-rays or electrons scattered by fibres of helical biological molecules and by carbon nanotubes (CNTs) from the unified point of view of the Fourier-Bessel transform of an atomic helix. This paper is intended for scientists who are not professional crystallographers. X-ray fibre diffraction patterns of Pauling's protein α-helix and of Crick and Pauling's protein coiled-coil are revisited. This is followed by a non-technical comparison between the historic x-ray diffraction patterns of the A and B conformations of DNA, which were crucial for the discovery of the double helix. The qualitative analysis of the diffraction images is supported by novel optical simulation experiments designed to pinpoint the gross structural informational content of the patterns. The spectacular helical structure of the tobacco mosaic virus determined by Rosalind Franklin and co-workers will then be described as an early example of the great power of x-ray crystallography in determining the structure of a large biomolecular edifice. After these mostly historical and didactic case studies, this paper will consider electron diffraction and transmission electron microscopy of CNTs of great current interest, focusing particularly on recent data obtained for single-wall, double-wall and scrolled nanotubes. Several points of convergence between the interpretations of the diffraction patterns of biological helices and CNTs will be emphasized.

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“…There are several works by A. A. Lucas, Phillipe Lambin, and others that provide complementary historical accounts of these events with less emphasis on the mathematical details of the X-ray diffraction analysis compared to the current work (5)(6)(7). Also, techniques to experimentally demonstrate in the classroom the X-ray diffraction of double helixes or other periodic patterns is outside the scope of this work but can be obtained from the Institute for Chemical Education and their excellent DNA Optical Transform Kit (8).…”

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confidence: 99%

X-ray Diffraction and the Discovery of the Structure of DNA. A Tutorial and Historical Account of James Watson and Francis Crick's Use of X-ray Diffraction in Their Discovery of the Double Helix Structure of DNA

Crouse

2007

J. Chem. Educ.

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A step-by-step method of teaching the X-ray diffraction analysis of DNA using the approach employed by James Watson, Francis Crick, Maurice Wilkins, Rosalind Franklin, and Raymond Gosling at an upper undergraduate and graduate level is described. This method includes a historical account of the 1953 articles by James Watson and Francis Crick, Maurice Wilkins et al., and Rosalind Franklin et al. Throughout the X-ray diffraction analysis, excerpts of their articles are included to describe the obstacles encountered by these researchers, the contributions each person made to the determination of the structure of DNA, and the degree to which X-ray diffraction aided their determination of the DNA structure. The article is organized with the assigned problem as the main part of the text and the intermediate steps leading to the solutions given in the Supplemental Material. Helpful hints and information are also given in the Supplemental Material. Writing the article in this way allows the project to be quickly implemented into upper-level undergraduate and graduate physics, chemistry, and materials science and engineering course curricula.

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Rosetta Stone of the genetic language

Cited by 6 publications

References 15 publications

A-DNA and B-DNA: Comparing Their Historical X-ray Fiber Diffraction Images

A-DNA and B-DNA: Comparing Their Historical X-ray Fiber Diffraction Images

Diffraction by DNA, carbon nanotubes and other helical nanostructures

X-ray Diffraction and the Discovery of the Structure of DNA. A Tutorial and Historical Account of James Watson and Francis Crick's Use of X-ray Diffraction in Their Discovery of the Double Helix Structure of DNA

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