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Biophysics and bioengineering

Biophysics and bioengineering

Physics and DNA

27 Mar 2003

It will not have escaped readers’ notice that the 50th anniversary of the discovery of the double-helix structure of DNA will soon be upon us. Countless articles, books, conferences and the like have been commissioned, written and organized to celebrate what is widely agreed to have been the single biggest advance in biology since Darwin proposed the theory of evolution through natural selection.


However, two aspects of the DNA story seem to have been overlooked amid all the discussions about the past, present and future of genetics. First, the double-helix structure emerged from a physics laboratory. Second, DNA is still the focus of intense study by a small band of physicists around the world. The aim of this special issue of Physics World is to add a physics perspective to the celebrations.

It would be churlish, of course, to claim that physicists discovered the double helix all on their own – to claim the “Bragging rights” as it were. After all, James Watson was a biologist. However, as Hugh Huxley describes in this issue in The Cavendish Laboratory and structural biology (p29, print version), a unique set of events and characters conspired to make the Cavendish Laboratory in Cambridge the home of the double helix.

In the 1930s the Cavendish was dominated by Ernest Rutherford and nuclear physics. However, when the legendary New Zealander died unexpectedly in 1937, the electors to the Cavendish chair of physics decided that nuclear physics had become too expensive for a university laboratory, and they opted to replace Rutherford with the crystallographer Lawrence Bragg. The Austrian-born chemist Max Perutz was already there, Francis Crick arrived in 1949 – having graduated with a degree in physics from University College London in 1937 – and Watson followed two years later. Whereas Watson was a mere 22 years old when he arrived in Cambridge, Crick was in his mid-thirties when he joined the Cavendish. Progress was slow to begin with and Crick was told to work on other projects. However, the pair persevered and the double-helix paper was published in Nature on 25 April 1953. The Nobel prize followed in 1962 and the rest, as they say, is history – except for the Rosalind Franklin question.

It does seem odd and unfair that neither Crick nor Watson mentioned Franklin, who died in 1958 aged just 37, in their Nobel speeches. However, that was more than 40 years ago and today Franklin is almost as well known as Crick and Watson. Indeed, as Robert Crease writes in The Rosalind Franklin question (p17, print version): “It is impossible to think about the discovery of DNA today without bringing to mind Rosalind Franklin.” It is time to move on.

Fast forward to 2003 and DNA is still fascinating from a physics point of view. John Marko and Simona Cocco describe experiments in which physicists measure the mechanical properties of single molecules of DNA in The micromechanics of DNA (p37, print version). Genetics is primarily interested in the order of the four bases – adenine (A), cytosine (C), guanine (G) and thymine (T) – on the double helix. However, the processes by which cells replicate and repair DNA are highly mechanical and their study requires a variety of tools and techniques from physics. And as attention turns to more complex structures such as enzyme-DNA interactions, the experiments will become even more demanding.

The double helix has a diameter of 2 nm, so it is not surprising that DNA is of considerable interest to researchers in nanotechnology. The fact that adenine always binds with thymine, and cytosine with guanine, also gives DNA built-in “intelligence” when used as an engineering material. As Andrew Turberfield explains in DNA as an engineering material (p43, print version), DNA has already been used as a molecular glue and as fuel for molecule tweezers. Moreover, a “DNA computer” recently solved what is probably the largest mathematical problem ever tackled using non-electronics means.

Other physicists have explored the electronic properties of DNA and its use as a scaffold for solid-state dye lasers. DNA might even be a superconductor. There are sure to be a few more twists and turns in the story of physics and DNA.

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