SEARCH

SEARCH BY CITATION

Keywords:

  • X-ray diffraction;
  • Watson–Crick double helix;
  • DNA

Abstract

The paper begins with a guided tour through the history of several major deciphering events in modern science, going from the determination of the wave nature of visible light in the early 19th century, via the discovery of X-rays and their electromagnetic nature around the turn of the 19th century, and onward to the great decipherments of molecular biology of recent times. The central piece of the latter decoding efforts, i.e., the measurement of the X-ray diffraction diagram of DNA, occurred in the middle of the 20th century and lead Watson and Crick to the discovery of the structure of the molecule. In the second part of the paper, a detailed analysis is given of the relationship between the gross features of the X-ray diagram and the corresponding structural elements of the doubly helical DNA backbone. In the third part, simple optical diffraction experiments, using a laser pointer and a single diffraction slide, are described which allow to mimic the X-ray diffraction experiment and reproduce all the major characteristics of the observed X-ray picture. Finally, the paper presents a quantitative description of the wave diffraction by an atomic helix and discusses the mathematical origin of the various features of the X-ray and optical patterns. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002