Biotechnology and Bioinformatics (1+1)

1.2.2. DNA Structure

Linus Pauling elucidated the - helix for DNA structure, an important feature of protein structure. Indeed, the a- helix, held together by hydrogen bonds, laid the intellectual ground work for the double helix model of DNA proposed by Watson and Crick. Maurice Wilkins and Rosalind Franklin used X-ray diffraction to analyse the three-dimensional structure of DNA at Kings College in London. Watson and Crick performed no experiments themselves. They used other group’s data to build a DNA model.

Erwin Chargaff studies (1950) of the base composition of DNAs from various sources revealed the following.

· The content of purines always equaled the content of pyrimidines.

· The amounts of adenine and thymine were always equal, as were the amounts of guanine and cytosine.

· These findings, known as Chargaff's rules, provided a valuable confirmation of Watson and Crick's model.

· The most crucial piece of the puzzle came from an X-ray diffraction picture of DNA taken by Franklin in 1952. Franklin's X-ray work strongly suggested that DNA was a helix.