On May 6, 1952, in a laboratory at King’s College London, what would be considered the most important photograph in all of history was taken. Photo 51 barely frames a surface of about 10 centimeters on a side, however, within its small area it contains the primordial structure of the human being and the solution to centuries of questions, which could be answered thanks to a young scientist named Rosalind Franklin. , which is credited with the first photograph of the DNA double helix.
Although Rosalind Franklin was the author of Photo 51, she was not awarded for it and therefore, the photograph not only represents one of the most important moments in science, but has also caused great controversy.
How was Photo 51 obtained?
Franklin did not obtain the image by mere chance, but rather invested many of her years as a chemist in the study of the human genome. Today we understand well that everything we are is contained in DNA, however, in 1952 it had barely been confirmed that this structure was made up of genes, but it was not known in what form or what it was like. Uncertain about exactly what the composition of DNA was, Franklin set about photographing the X-ray diffraction pattern of deoxyribonucleic acid and got a great response.
Crystallography is a technique that is based on the determination of the three-dimensional structure of a crystal and as an expert in this area, Rosalind Franklin used it to obtain the first photograph of DNA, thereby discovering the double helix that makes it up. It was not an easy job, in fact, the British chemist had to expose DNA fibers to X-rays for a total of 62 hours.
Photo 51, as his greatest find was named, was not Franklin’s first attempt to photograph human DNA. He previously carried out many other experiments but little by little he improved his data collection methods.
He noticed that DNA fibers with a higher water content produced a different diffraction pattern than DNA fibers with a lower water content. That is to say, the three-dimensional structure of DNA is modified depending on its hydration. The form of DNA with the lowest water content was named by Franklin as DNA A and the one with the highest water content as DNA B. Today these designations continue to be used to refer to the structure of deoxyribonucleic acid and today it is known that form A is adopted when DNA is subjected to artificially created environmental conditions.
The discovery of the double helix
But it was exactly on May 6, 1952 when the chemist decided to pump hydrogen gas into the DNA fibers through a saline solution, to maintain the hydration of the sample and then exposed the deoxyribonucleic acid to X-rays for 62 hours. During this period, the electromagnetic waves of X-rays interacted with the electrons in the DNA crystals and diffracted at angles that indicated the arrangement of their atoms. In other words, the X-rays drew the shape of deoxyribonucleic acid on a large scale.
Franklin collected the resulting diffraction pattern and labeled it with the number 51, which later became Photo 51, thanks to which it was learned that DNA has a structure of two strands that meander around each other. And furthermore, it contains all the genetic code that determines us as living beings.