Discuss the chain of events that led to the discovery of DNA as the heritable substance and the discovery of the structure of DNA. Ans> The chain of events led to the discovery of DNA as the heritable substance and the discovery of the structure of DNA. In the late nineteenth century, a German biochemist Friedrich Miescher found the nucleic acids which are long-chain polymers of nucleotides, and are made up of sugar, phosphoric acid, and several nitrogen-containing bases. Later it was found that the sugar in nucleic acid can be ribose or deoxyribose, giving two formsie RNA and DNA.In 1943, American Oswald Avery proved that DNA carries genetic information.
He even suggested DNA might actually be the gene. Usually people thought that the gene would be protein, not nucleic acid, but by the late 1940s, DNA was largely accepted as the genetic molecule. In 1948, Linus Pauling discovered that many proteins take the shape of an alpha helix, spiraled like a spring coil. In 1950, Erwin Chargaff found that the arrangement of nitrogen bases in DNA varied widely, but the amount of certain bases always occurred in a one-to-one ratio.In the early 1950s, there was a race to discover DNA among scientists. At Cambridge University, Francis Crick along with James Watson showed a great interest and were impressed by Pauling’s work. Meanwhile in London, Maurice Wilkins and Rosalind Franklin were also studying DNA.
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The Cambridge team’s approach was to make physical models to narrow down the possibilities and eventually create an accurate picture of the molecule. The london team took an experimental approach, looking particularly at x-ray diffraction images of DNA.In 1951, Watson attended a lecture by Franklin. She had found that DNA can exist in two forms, depending on the relative humidity in the surrounding air which helped her deduce that the phosphate part of the molecule was on the outside. Watson and crick based on this information, made a failed model. It caused the head of their unit to tell them to stop DNA research. Franklin, working mostly alone, found that her x-ray diffractions showed that the “wet” form of DNA (in the higher humidity) had all the characteristics of a helix.
She suspected that all DNA was helical but did not announce her finding as she dint had sufficient evidence on the other form as well. Wilkins in 1953, showed Franklin’s results to Watson, apparently without her knowledge. Watson and Crick took a crucial conceptual step, suggesting the molecule was made of two chains of nucleotides, each in a helix as Franklin had found, but one going up and the other going down. Crick had just learned of Chargaff’s findings about base pairs.He added that to the model, so that matching base pairs interlocked in the middle of the double helix to keep the distance between the chains constant. Watson and Crick showed that each strand of the DNA molecule was a template for the other. During cell division the two strands separate and on each strand a new “other half” is built, just like the one before.
This way DNA can reproduce itself without changing its structure — except for occasional errors, or mutations.The structure so perfectly fit the experimental data that it was almost immediately accepted. DNA’s discovery has been called the most important biological work of the last 100 years. By 1962, when Watson, Crick, and Wilkins won the Nobel Prize for physiology/medicine, Franklin had died. References: 1; http://en. wikipedia. org/wiki/History_of_molecular_biology 2; http://en.
wikipedia. org/wiki/DNA 3; http://en. wikipedia. org/wiki/Rosalind_Franklin 4; http://www. biomath. nyu. edu/index/course/hw_articles/nature3.