The man who turned our lives into a piece of information

 In July 2004, Francis Crick, the scientist who discovered the structure of DNA, died. He was accused of stealing the discovery from another scientist, but his partner in the discovery claimed that at the time their only reading material was the fashion magazine "Vogue" 

16.8.2004

By: Michael Rosenberg

(Published in "Globes" on August 5-4, 2004 and published on the website of the scientist with the permission of the author)

Direct link to this page: https://www.hayadan.org.il/rosenberg004.html

Last Thursday, Francis Crick, the British scientist who deciphered the structure of DNA, the substance that stores all the hereditary information of a living organism, died at the age of 88. The discovery of the structure of DNA is one of the most important scientific achievements of the last millennium. The applications of this discovery will apparently be evident in the next hundreds of years in the science of genetic engineering. The discovery of DNA embodies a fascinating plot that contains all the elements of a detective novel full of unexpected turns.

In 1866, a monk from Bohemia named Georg Mendel published the laws of heredity. Mendel, who conducted hybridization experiments with pea seedlings, hinted at "units of heredity" passing from generation to generation, but at the time nothing was known about those "units": neither their nature, nor their composition, nor their location in the living body. In fact, Mendel's work was almost unknown to the scientific community until the end of the 19th century. It was clear to the researchers that the hereditary information must be carried by a certain substance found in the organism. Since the substances that make up the living body were discovered, the natural candidate to be the bearer of the hereditary load was the protein. This is because the material carrying this enormous amount of information must be a complex material. The protein seems suitable for the task as it is a chemical chain of variable length made up of 20 types of subunits (amino acids) arranged in different variations.

In 1928, researcher Frederick Griffith discovered a "property-transferring" substance that turned harmless bacteria into deadly bacteria that cause pneumonia. However, Griffith was unable to decipher the composition of that substance. In 1943, the researcher James Avery conducted a follow-up experiment in which he showed that Griffith's "hereditary material" is nucleic acid - a relatively simple substance that is found in the nucleus of the living cell and is made up of a chain of only four types of subunits (nucleotides) - A, C, T and -G. Avery's conclusion remains controversial - scientists found it difficult to accept that such a simple substance as nucleic acid is capable of carrying on its back the set of hereditary traits. Nucleic acid itself was actually discovered back in 1869 by a researcher named Johann Miescher, when he managed to isolate it from pus collected from surgical bandages. Miescher discovered that the nucleic acid contained phosphorus but his work did not attract scientific attention. It took science about 75 years to point out the surprising connection between that nucleic acid and the "hereditary material" whose identity they were looking for, and still, this connection was in doubt. It was only in 1952 that the scientific community unquestioningly accepted the nucleic acid DNA as carrying the genetic load. This follows an experiment conducted by Alfred Hershey and Martha Chase, in which they marked the phosphorus in the DNA of a certain virus with a radioactive isotope (a kind of "dyeing" that allows identification through the absorption of typical radioactive radiation). The experiment proved most clearly that the hereditary material carrying the code of life is the nucleic acid DNA, and not the protein.

At this point it is already clear to researchers that the role of DNA is cardinal in everything related to the origin of life. The DNA is the substance that stores within it all the information needed for a single fertilized cell of a fly to develop into a fly and a single fertilized cell of a human to eventually develop into a human. At the same time as solving the riddle of the identity of the hereditary material, in the early fifties the race began to solve the following fascinating riddle: "How does DNA manage to store this enormous amount of information?"

DNA consists of a total of four types of simple subunits, hence the secret of DNA must lie in a unique structure that enables the storage of hereditary information and its transmission. A researcher named Erwin Chargaff discovered in 1949 that there is always a match between the number of subunits A and T and between C and G. Chargaff commented that this is a "noticeable, but perhaps insignificant trend". At the same time, a researcher named Rosalind Franklin joined the task of discovering the structure of DNA using x-rays of the DNA molecule, in her x-rays a clear X shape is visible that already hints at the structure of a helix.
Franklin and her research partner Maurice Wilkins were very close to discovering the double helix structure of DNA and even suggested it as one of the possibilities.

At this point Francis Crick and his American partner James Watson entered the picture - a pair of young, cautious and motivated students who studied at King's College in Cambridge. It is said that they used to spend more time in the "Hanesher" pub across from the college than in the laboratories. Another legend holds that the structure of the double helix was discovered by Watson and Crick when they were sitting at their regular table in the "Eagle" pub, and in their kindness with a fine English beer, they played with the paper napkins and twisted them into a helix. What is known is that one of Rosalind Franklin's x-rays was passed on to Watson without her knowledge by her partner Willikens, who was at odds with her and accused her of not sharing her findings with him. Watson, for his part, once claimed that the only reading material that he and Crick used to read at that time was "Vogue" magazine. Apparently, Watson and Crick combined the X-ray appearance from Rosalind Franklin's X-ray with Chargaff's findings, and concluded that DNA has a double helix structure in which the four subunits appear as fixed pairs: A vs. T, and C vs. G. This unique structure , is what enables the transfer of hereditary information, since if one side of the coil is, for example, AATACGAG, then the other side must be TTATGCTC. Thus, by cutting the molecule in half and completing each of the halves, exact copies of the original molecule will be created. Watson and Crick published their inventions in April 1953 in the journal "Nature" and in 1962 won the Nobel Prize for it. Rosalind Franklin died in 1958 of cancer (probably due to her exposure to X-rays) and thus prevented her from sharing the world fame that Watson and Crick won.