Question
1.Discuss how the unique physical and chemical properties of water contribute to the importance of water for life on Earth to survive.
2.Discuss how the methods of experimentation and observation have changed throughout the history of science.
3.Explain the role so called “accidental” discoveries played in the history of science.
4.Describe the major experiments and scientists involved in the discovery of DNA as our hereditary material and its structure.
5.Explain what role women played in the Scientific Revolution of the 18th Century? What role do women in science play today?This assignment will be worth 20% of your grade. Your paper should be creative and interesting, and should be a minimum 1500 to 2000 words in length. It should be well-organized and demonstrate an orderly flow of information that clearly addresses the subject chosen.
Answer
The Discovery of DNA
The discovery of DNA as the hereditary material and its structure marked a major milestone in the understanding of genetics and transfer of hereditary information. In the mid twentieth century, scientists were able to get a clear understanding of the structure and chemical nature of DNA. Prior to this, various speculations existed on what kind of molecules carried hereditary information. Some scientists associated transfer of hereditary information to proteins, while others speculated that transfer of hereditary information was facilitated by unknown molecules which they had yet discovered. Eventually, DNA was identified as the molecule responsible for the transfer of hereditary information across generations.
DNA was first identified by Friedrich Miescher and subsequently named “nuclein” in 1869 (Betz, 2011). Nuclein was later called nucleic acid and finally deoxyribonucleic acid (DNA). Miescher was at the time studying white blood cells. The task involved isolating the different molecules that make up cells. He was able to isolate the DNA molecule as a discrete molecule alongside its associated proteins. The experiments further revealed that the nuclein molecule was composed of phosphorous, hydrogen, oxygen and nitrogen. In addition, the ratio of phosphorous to nitrogen was unique. Interestingly, Miescher associated proteins with the transfer of hereditary information due to the wide variety in which they were found. His belief was in accordance with those of other scientists of the time. Nonetheless, his research laid the foundation for more research in molecules and the DNA (Betz, 2011).
The link between DNA and hereditary information was only discovered much later, precisely in 1944 by a biologist known as Oswald Avery (Alcamo, 2001). Prior to this, other scientists had carried out extensive experiments on DNA research to establish what controlled heredity. Gregor Mendel’s experiments for instance indicated that inherited traits were controlled by what he termed as factors that were derived from parents. Mendel conducted extensive research with pea plants which revealed that parents passed on certain traits to their offspring. The experiments also revealed that certain factors became dominant over other factors. In early 1900, Mendel’s observations were verified after it was noted that the factors which determined inheritance were actually chromosomes (Alcamo, 2001). Other experiments by scientists such as Morgan in 1910 verified Mendel’s observations. Morgan noted that the white eye color in some fruit flies was the result of a single chromosome.
Oswald Avery conducted investigations on heredity using the bacteria responsible for pneumonia. These bacteria were classified into two types; the S type bacteria and the R type bacteria. The S type bacteria were enclosed by an outer layer known as capsule, while the R type bacteria did not have a capsule or the outer layer (Seising, 2009). Avery’s experiments indicated that the DNA was responsible for the changes in the outer structure of the pneumonia bacteria. Thus, DNA could alter the characteristics of the bacteria, changing the R type pneumonia bacteria into the S form. Other molecules proteins did not have the potential for bringing changes in the outer structure of the bacteria. This led to the conclusion that DNA contained the hereditary information that was passed from one generation to the next one. Oswald Avery’s experiments and findings were supported by other biologists such as Colin Macleod and Maclyn McCarty (Seising, 2009).
Oswald Avery’s experiments were confirmed almost a decade later by scientists Martha Chase and Alfred Hershey (Alcamo, 2001). The duo conducted separate experiments on heredity which indicated that proteins had no role to play in the transfer of hereditary information. They used bacteriophages in their experiments to determine the transfer of hereditary information. Bacteriophages are those viruses that can infect and replicate within bacteria. They are primarily composed of DNA and protein (Alcamo, 2001). The duo employed radioactive labels in their experiments. The radioactive labels were designed to precisely integrate with either the protein or DNA, but not integrate in both. The duo showed that the action of bacteriophages involves infecting the bacterial cell with their own DNA, ultimately leading to the development of multiple copies of the viruses. The experimental results thus indicated that the injected DNA had an active role to play in directing the production of new viruses in the bacterial cells. Although it was not clearly understood how replication of new viruses occurred, new research over time found that the new DNA guides the formation of only the viral DNA in bacterial cells.
Following the discovery of the role of the DNA in transfer of hereditary information across generations, scientists still had a vague understanding of the structure of a DNA molecule. In the 1950s, scientists were more inclined in deciphering the structure of DNA. The drive to understand the structure of DNA was as a result of two reasons: to start with, understanding the structure of the DNA meant that scientists could be able to clearly tell how the DNA functions during the hereditary process; secondly, understanding the structure of the molecule could enable scientists to know how DNA is duplicated in cellular reproduction (Alcamo, 2001). Cellular reproduction and transfer of genetic information are the fundamental processes which scientists seek to understand. Understanding of structure of the DNA was an important breakthrough in the 20th century. It enabled scientists to understand how heredity works in detail.
In 1953, James Watson and Francis Crick made yet another scientific breakthrough in understanding heredity, specifically in shedding light on the structure of the DNA. The duo discovered the double-helix structure of the DNA which significantly changed molecular biologists’ understanding of the DNA (Tobin & Dusheck, 2005). Prior to the discovery, scientists held the view that the DNA was triple stranded. This was the assumption found in many textbooks and the view held by many. These incorrect assumptions made it difficult for scientists to understand how DNA works. The discovery of the true DNA structure significantly helped in the development of various gene techniques such as rapid gene sequencing, understanding monoclonal antibodies, development in the field of genetic engineering and lastly helped develop the biotechnology industry.
Watson and Crick knew that understanding the structure of the DNA would shed light in the field of molecular biology. The duo conducted no experiments of their own, but dwelled on the experimental works of other molecular scientists in deciphering the structure of the DNA (Lewis, 2009). Watson and Crick employed the use of stick-and-ball models in order to arrive on possible structures of the DNA. Over a period of two years, the duo became immersed in various fields of science such as genetics, physical chemistry, chemistry, X-ray crystallography and biochemistry. Crick had extensive knowledge in X-ray crystallography and physics while Watson had a deep understanding of bacterial and viral genetics. This, combined with other factors such as persistence, brilliance and luck enabled them to correctly come up with the double helix structure of the DNA. The duo was able to show that DNA is not only simple but also complex enough to be the one responsible for passing of hereditary information across generations.
In early 1950s, numerous researches existed on the structure of the DNA; however, the findings were unconnected and offered little or no insight into the true structure of the DNA. Watson and Crick took it upon themselves to develop a comprehensive theory of heredity by analyzing the existing researches and drawing connections from the different findings. Alexander Todd, a renowned organic chemist at the time had already concluded that a DNA molecule comprised of repeating deoxyribose sugar groups and phosphate groups. Erwin Chargaff had discovered that the bases adenine, guanine, cytosine, and thymine, as well as the amount of DNA varied widely across species. He also noted that A & T, and G & C occurred in specific rations of one-to-one (Lewis, 2009). Other biologists such as Rosalind Franklin and Maurice Wilkins were also instrumental in understanding the structure of the DNA molecule. Franklin and Maurice employed the use of X-rays to understand the structure of the DNA.
Shining X-rays on biological molecules such as deoxyribonucleic acid can enable researchers observe complex patterns and hence determine the structure of the DNA. Although Franklin and Maurice obtained the diffraction photos from DNA, they were still unable to comprehensively draw on the structure of the DNA. In 1953 Watson and Crick, working on drawing connections between various scientific researches, stumbled upon Franklin and Maurice’s DNA X-ray diffraction photos which they had taken during their experiments (Tobin & Dusheck, 2005). The photo provided Watson and Crick with clues about the actual structure of a DNA molecule. The photo had what appeared as a fuzzy X at the center of the molecule, which pointed towards a helical structure of the DNA.
Drawing on experimental works from other scientists, Watson and Crick were able to learn the true structure of a DNA molecule. They also came to learn that most textbooks were wrong on the idea of how the elements carbon, hydrogen, nitrogen and oxygen are configured in guanine and thymine. In the earlier incorrect understanding, hydrogen atom was joined to an oxygen atom, while in the new and correct understanding, a hydrogen atom bonds with a nitrogen atom (Tobin & Dusheck, 2005). It is then that Watson realized that A always joined with T, and C with G. The pairs were held together by hydrogen bonds. In addition, Watson realized that the observation supported Chargaff’s conclusions on the ratios in which A & T, and G & C occurred. Watson and Crick thus discovered the double helix structure of the DNA.
References
Alcamo, I. E. (2001). DNA technology: The awesome skill. San Diego: Academic Press.
Betz, F. (2011). Managing science: Methodology and organization of research. New York: Springer.
Lewis, R. (2009). Discovery: Science as a Window to the World. Chichester: John Wiley & Sons.
Seising, R. (2009). Views on fuzzy sets and systems from different perspectives: Philosophy and logic, criticisms and applications. Berlin: Springer.
Tobin, A. J., & Dusheck, J. (2005). Asking about life. Belmont, Calif: Brooks/Cole
