Modern (1940’s-present)
40
Mary Hannah Rodgers
introduction
The discovery of the structure of DNA has lead to major accomplishments and medical advancements. Not only was the discovery essential to the progress of the field of genetics, but also impacted society beneficially. The experiments done by Erwin Chargaff, Rosalind Franklin, James Watson and Francis Crick led to the discovery of the structure of DNA and the beginning of modern genetics, which lead to a greater understanding of diseases in society like cancer and how to prevent them from invading communities and taking human lives.
Background
The understanding of genetics and DNA has increased in the past ten years due to increased technological advancement and scientific discoveries. However, in order for this to be possible, the foundation of genetics and the definition of DNA had to be established first. Genetics is the study of heredity and how organisms inherit information from one generation to the next.
At one point, there was uncertainty surrounding which molecule in an organism was responsible for passing information down to offspring. In 1928, Frederick Griffith discovered that DNA was the molecule that carries information for the cell to produce proteins and process different functions in the organism (Encyclopedia Britannica, 2020).
DNA, or deoxyribonucleic acid, is defined as a macromolecule that carries information in the cell. The name deoxyribonucleic acid comes from the fact that DNA contains a deoxyribose sugar, named such because it is missing an oxygen, and is a nucleic acid macromolecule (Sinden, 2012). It is primarily located in the nucleus of cells and is made of 2 strands arranged in a double helix structure. These strands are antiparallel, with one strand running in the opposite direction of the other. Each strand is composed of a covalently linked phosphate sugar backbone and 4 different nitrogenous bases, cytosine, thymine, guanine, and adenine, that hydrogen bond to the other strand in the helix (Sinden, 2012). The order in which the 4 nitrogenous bases are arranged corresponds to different information in the cell (Sinden, 2012).
This is how we define and understand DNA currently, but this information wasn’t always accessible in society. It took multiple experiments done by multiple different scientists in order to discover this concept.
Before the 1900s, Aristotle and Gregor Mendel were the main scientists that contributed to the study of genetics and its impact on society. Aristotle postulated that heredity was based on information being passed down through semen and the mother’s …until the discoveries of Erwin Chargaff, Rosalind Franklin, James Watson and Francis Crick in the 1900s, there was no knowledge of DNA, its structure, or function. blood. Mendel discovered the accepted model of inheritance for organisms using pea plants and the different traits they possessed (Sinden, 2012). However, until the discoveries of Erwin Chargaff, Rosalind Franklin, James Watson and Francis Crick in the 1900s, there was no knowledge of DNA, its structure, or its function.
Impact on Society
The discovery of the structure of DNA was an essential breakthrough for the field of genetics and its progression throughout history. Determining more about the structure impacted society on a global level due to the fact that every country was or would be struggling with disease at some point and could benefit from increased knowledge regarding the medium through which diseases arose. Even today we do not know The structure of DNA was the foundation and building block necessary for all other analyses of diseases and disorders.everything there is to know about every disease. However, because it was the foundation and building block necessary for all other analyses of diseases and disorders, the discovery of the structure of DNA flourished in this time period and started a movement of even more discoveries.
Modern genetics uses the structure and function of DNA to figure out how diseases work in the body and how to prevent or stop them. The functional unit of DNA, otherwise known as a gene, encodes for information in the cell that can be transcribed and translated to make proteins that do work in the organism. These genes can easily be mutated sometimes and these mutations are changes in the DNA that are capable of leading to disease or dysfunction. For this reason, it is important that we understand the structure of DNA and how or why it functions the way it does, in order to stop mutations from leading to diseases and causing harm in organisms.
Experiments of Erwin Chargaff
Erwin Chargaff was the first of the geneticists to start the process of accumulation of information regarding the structure of DNA. He started his experiments in 1944, where he was curious about the composition of DNA in different organisms. At this point, he was aware of the postulations and findings of both Aristotle and Mendel when it came to genetics as a study of inheritance. However, he was more concerned with the actual molecule that was used for inheritance and the carrying of information.
Using paper chromatography and UV spectrophotometry, Chargaff was able to separate the nitrogenous bases and calculate their abundance in the DNA molecule (Brown, 2018). He discovered that the number of adenine bases equals the number of thymine bases and the number of cytosine bases equals the number of guanine bases (Brown, 2018). Even as he compared this experiment between organisms, he found that the ratio of base pairs still held true. By comparing the components of DNA between different organisms, he was able to conclude that DNA was responsible for genetic diversity, as it varied between organisms.
This has become what geneticists call the base pairing rules, leading to the fact that adenine (A) always pairs with thymine (T) and cytosine (C) always pairs with guanine (G). Chargaff’s discovery was essential to the overall understanding of the structure of DNA. The basis of how the two strands of DNA fit together is solely dependent on the fact that A and T base pair together and C and G base pair together. This is essential to modern genetics today because geneticists can use these base pair rules to discern mutations in the DNA between base pairs and possibly how they arose. This information is helpful in providing pathways in order to fix or prevent mutations in the DNA that can lead to very harmful diseases or disorders.
Experiments of Rosalind Franklin
Another scientist who contributed to the discovery of the structure of DNA was Rosalind Franklin. Franklin conducted her experiments in 1951 using X-ray crystallography (Braun, 2011). She was aware of the base pair rules that had just been established by Chargaff and wanted to expand on them by determining more information about the structure of DNA.
Franklin used X-ray crystallography, a form of taking photographs, to capture the DNA molecule and discern its configuration. Through her diligence and persistence, Franklin was able to obtain a picture of DNA that revealed its structure. In doing so, she discovered that the DNA molecule was in fact configured in a helical structure (Braun, 2011). However, she didn’t know whether it was a double or triple helix.
This was a breakthrough in the study of DNA structure and ultimately led to what it is the accepted idea today. Her discovery was passed on to James Watson and Francis Crick after her death, who are accredited with the discovery of the structure of DNA (Jensen, 2019). The helical structure is a necessary part to how DNA functions and carries information throughout the cell. Because DNA is configured this way, it is able to unwind in order to replicate and transcribe proteins for functions in the organism.
Modern geneticists use the knowledge of the helical structure to determine how mutations occur in the replication and transcription processes of DNA. This is where many mutations can arise and cause harmful diseases in the genes of a DNA helix. Because of the discovery of the helical structure of DNA, modern geneticists are now able to use this information to create ways in which to prevent harmful medical conditions caused by mutations in the DNA.
Experiments of Watson and Crick
The last scientists that officially culminated all of the information discovered in past experiments to establish the structure of DNA were James Watson and Francis Crick. These two scientists are credited with discovering the structure of DNA as it is known today. Instead of actually performing an experiment however, they used the information they already knew, courtesy of Erwin Chargaff and Rosalind Franklin. The experimental process that they went through to make the discovery included building a model of DNA for a better understanding of how it fit together so to speak.
By using this method, they were able to see how the helical structure and base pair rules worked together in order to become the whole structure of DNA (National Institutes of Health, n.d.). They established that the backbone of the molecule was composed of phosphates and deoxyribose sugars covalently bonded, as seen in the model. They also established that the two strands hydrogen bond together through the 4 nitrogenous bases (Watson & Crick, 1953).
It is extremely essential that the whole structure of DNA is understood and can be studied for modern genetics purposes. Because the structure of DNA can be studied and more experiments can be done on it, more problems or mutations in the molecule can be discovered and potentially stopped or prevented. However, without this knowledge of the structure, the function and potential mutations in the function of DNA could not be understood fully. According to an article written by John Burn, the benefits that could come from the discovery of the structure of DNA have yet to reach their full potential (Burn, 2007).
Practical Applications in Society
Chargaff, Franklin, Watson, and Crick were able to jumpstart the era of modern genetics by discovering the basis of how organisms know how to function, or the molecule of DNA. The most prominent example of how this has affected modern genetics is through the human genome project (Burn, 2007). This project has been able to determine the sequence of nucleotides present in many genetic disorders using the structure of DNA. Because they can sequence genetic disorders, they can determine how disorders and diseases work and possibly find a way to alter these sequences beneficially. This could potentially lead to cures to many of the diseases that affect our societies globally.
We can also use the structure of DNA to manufacture medicines. For example, the sequence of the human insulin gene was used to develop a man-made insulin substitute for people with diabetes, greatly increasing their quality of life (Burn, 2007). Also, before infants are born, they are screened in order to determine whether their genome has sequences indicating diseases like phenylketonuria (Burn, 2007).
These are all real-world, practical examples that save lives daily, solely based on the fact that we know the structure of DNA and in turn how to sequences nucleotides as a part of whole genomes. This is crucial to the betterment of society as a whole, including the survival rate and quality of life for countries around the world.
All three of these experiments contributed to the discovery of the official structure of DNA as geneticists describe it today. The experiments done by Chargaff, Franklin, and Watson and Crick as a whole were essential to starting the era of modern genetics, which lead to a greater understanding of the diseases that pervade society and humankind.
Modern genetics uses the accepted structure of DNA to infer and experiment solutions regarding mutations that lead to harmful diseases. If scientists can understand how mutations affect the structure of DNA, they can generate methods to prevent these alterations and save lives.For example, certain mutations in the structure of DNA can lead to cystic fibrosis, sickle cell anemia, and types of cancers (Mutations and Disease, n.d.). These are all diseases that can be very fatal. However, if scientists can understand how these mutations affect the true structure of DNA, they can prevent these changes, potentially saving many lives and finding cures to diseases.
Chapter Questions
- True/False: Watson and Crick are the only scientists that contributed to the discovery of the structure of DNA.
- Multiple Choice: Which scientist used X-ray crystallography to discover the helical structure of DNA?
A. Rosalind Franklin B. Maurice Wilkins C. Francis Crick D. James Watson E. Erwin Chargaff - Short Answer: What are examples of real-world applications that the structure of DNA has contributed to?
References
Braun, G., Tierney, D., & Schmitzer, H. (2011). How Rosalind Franklin Discovered the Helical Structure of DNA: Experiments in Diffraction. The Physics Teacher, 49(3), 140–143. doi: 10.1119/1.3555496
Encyclopedia Britannica. (2020, February 16). Oswald Avery. In Encyclopedia Britannica. Retrieved from https://www.britannica.com/biography/Oswald-Avery#ref700379.
Brown, T. A. (2018). Genomes. New York: Garland Science.
Burn, J. (2007). Discovery of structure of DNA: the best is yet to come. British Medical Journal (BMJ), 334(suppl_1). Doi: 10.1136/bmj.39051.647963.94
Jensen, R. E., Parks, M. M., Mann, B. W., Maison, K., & Krall, M. A. (2019). Mapping Nature’s scientist: The posthumous demarcation of Rosalind Franklin’s crystallographic data. Quarterly Journal of Speech, 105(3), 297–318. doi: 10.1080/00335630.2019.1629000
Mutations and Disease. (n.d.). In The Tech Interactive, Stanford at the Tech. Retrieved from https://genetics.thetech.org/about-genetics/mutations-and-disease.
National Institutes of Health. (n.d.). The Francis Crick Papers: The Discovery of the Double Helix, 1951-1953. In U.S. National Library of Medicine: Profiles in Science Retrieved from https://profiles.nlm.nih.gov/SC/Views/Exhibit/narrative/doublehelix.html
Sinden, R. R. (2012). DNA Structure and Function. Burlington: Elsevier Science.
Watson, J. D., & Crick, F. H. (1953). Molecular structure of nucleic acids. Nature: International Journal of Science, 171, 737–738. doi: https://doi.org/10.1038/171737a0
Figures
“The Chemical Structure of DNA” by Andy Brunning, Compound Interest 2018 is licensed under CC BY-NC-ND 4.0
“DNA chemical structure” by Madeleine Ball, Wikimedia Commons 2018 is in the Public Domain, CC0
“Crick and Watson’s DNA molecular model | Science Museum Group Collection” by Francis Crick is licensed under CC BY-NC-SA NULL