DNA in Basic and Applied Science: From the Building Blocks of Life to Heredity and Catching Bad GuysRead Now
I have been watching true crime documentaries involving cold cases. Cold cases are crimes that went “cold” due to lack of progress in the investigation. What is remarkable about some of these cold cases is that many of them were solved decades after the crime thanks to DNA evidence. DNA technology along with national databases of DNA profiles of convicted offenders and arrestees, as well as coordination among law enforcement agencies, has brought about a revolution in crimefighting and greatly increased the odds of catching the criminals.
But how did this come about? The answer: is curiosity. Scientists reasoned that biological entities must be made of basic parts or building blocks that are put together to create the whole. Thus the original research into living things was a quest to find, describe, and understand the nature of these building blocks, how they fit together, and how they work.
In 1869 the Swiss physician Friedrich Miescher was working in the city of Tübingen in Germany with the cells present in the pus that he painstakingly isolated from surgical bandages. While preparing a solution from these cells he noticed a material that precipitated out of the solution when he acidified it. Miescher would go on to demonstrate that this material, which was not made of proteins or lipids, was present in the nucleus of the cells and he called it nuclein (which we now know to be DNA). Miescher later worked in obtaining purer extracts of nuclein and analyzing its composition, and he also discovered that sperm were a particularly good source of nuclein. His work with sperm led him to become interested in heredity, but he never considered that nuclein could be solely responsible for it.
Scientists kept on gaining a more profound understanding of the makeup of nuclein and its properties. For example, in 1881 the German biochemist Albrecht Kossel found that nuclein contained four nitrogen containing bases, adenine (A), cytosine (C), guanine (G), and thymine (T). In that same time period, it was becoming evident that the nucleus of cells played an important role in cell division and multiplication and perhaps heredity. Based on multiple lines of evidence, in 1882 the German biologist Walther Flemming suggested that the chromosomes, which are structures that can be found inside the nucleus, contained nuclein, and in 1902 Theodor Boveri and Walter Sutton independently postulated that chromosomes were involved in heredity.
The early 20th century saw the rise of the field of genetics and triggered the search for the physical nature of the unit of inheritance: the gene. Thomas Morgan proposed in 1911 that genes were present in chromosomes. Although some scientists began to entertain the notion that nuclein, now renamed “nucleic acid” could be responsible for heredity, many still favored proteins as they did not understand how the chemical makeup of nucleic acid could be responsible for it. This issue was finally solved when Oswald Avery, Colin MacLeod, and Maclyn McCarty working with bacteria in 1944, and Alfred Hershey and Martha Chase working with viruses in 1952 demonstrated that the molecule responsible for heredity was the nucleic acid which is now formally called DNA (deoxyribonucleic acid).
A series of discoveries then followed not only regarding the nature of DNA but how to work with it. James Watson and Francis Crick in 1953 proposed their famous “double helix” model for the structure of DNA and suggested a mechanism by which it could carry the genetic information. In 1956 Arthur Kornberg discovered the enzyme that replicates DNA (DNA polymerase). From 1961 to 1966 the genetic code was cracked by several scientists including Robert Holley, Gobind Khorana, Heinrich Matthaei, and Marshall Nirenberg. In 1977 Frederick Sanger, Allan Maxam, and Walter Gilbert developed methods to sequence DNA, which were vastly improved when Kary Mullis in 1985 developed the process of the polymerase chain reaction (PCR). The PCR process allowed the production of large number of copies of DNA from small samples.
As the mechanisms of heredity at the molecular level became clearer, scientists began asking other questions such as the role of genes in disease and in other important biological processes which ushered a revolution in medicine and the biological sciences that is still ongoing. But at the same time, other groups of scientists begun asking different types of questions. They wondered if DNA could be used to develop practical applications.
In 1984 the British scientist, Alec Jeffreys, succeeded in creating the first genetic fingerprint of a human being, and he began applying his genetic fingerprinting techniques to settle paternity disputes and immigration cases. He also began adapting his techniques for use in criminal cases; something which he called genetic profiling for forensic use. In 1986 the police contacted him to solve the case of two women who had been raped and murdered. Using DNA evidence, Jeffreys not only proved that a man arrested for the crime was innocent, but he also succeeded in finding the criminal from samples of individuals that the police had obtained from the area.
From there on, the use of DNA profiling greatly increased in the forensics field and was improved to the point that today even a small droplet or stain from a biological fluid or a single hair with a follicle left at the scene of a crime can be used to produce enough DNA to aid in establishing the innocence or culpability of a subject. And the future may hold even more amazing forensic applications of the process. Today’s DNA profiling methods are effective if a match can be found in a database or in a sample from a suspect. However, even in the absence of a match, DNA profiling has the potential to reveal key aspects about the originator of the sample being profiled such as eye, hair, and skin color, and probable physical appearance.
And all this started because some scientists were curious about what living things are made of.
DNA image by Виталий Смолыгин is in the public domain.