Chemistry

Dna Deoxyribonuecleic Acid James d Watson Francis Crick Rosalind Franklin Linus Pauling



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The acronym "DNA," stands for "Deoxyribose Neucleic Acid." If you are a chemist, biologist or associated with some other scientific discipline which deals with such terminology, then you know exactly what I am talking about when I make reference to this chemical composition. For the rest of the lay people out there, a little more definition might be helpful.

In fact, DNA stands for a lot of different things to a lot of different people in today's world. To a geneticist, it is the blueprint of life and the secret to resolving many of the diseases, syndromes, and conditions, which afflict the human species. To pharmaceutical companies, this stuff is pure gold waiting to be mined for huge profit. To biologists, DNA is the mechanism of heredity which Charles Darwin new nothing about, but which is the proof positive of his theory of variation through natural selection. To wrongly convicted people sitting on death row and awaiting execution, DNA has, over and over again, been the instrument of reprieve and exoneration. To you and me and the rest of the 6 billion or so humans that now inhabit planet earth, DNA is who we are; it defines everything about us from what we look like to how we feel. So, as you can see, DNA is some pretty special stuff.

In 1871, Johan Friedrich Miechner, isolated some phosphate rich chemicals from the nucleus of white blood cells. He called the substance "nuclein." He of course lacked the sophisticated technology needed to study this substance at a molecular level, but he had determined through experimentation that some how this was the life giving entity found in all living cells.

Over the next five decades the nature of chemical elements and how they interact with each other would unfold, opening the door to a whole new field of chemical and biological science called molecular biology. Pioneers in this new field like scientist Fred Griffith, physicist Erwin Schrodinger, Oswald Avery, and Linus Pauling, to name a few, began to methodically unlock the secrets of the microminiature world inside the nuecleus of cells; and understand its underlying chemistry. Rosalind Franklin, an X-ray crystallographer working with Maurice Wilkins at his Kings College laboratory in London would make a key discovery about the chemical structure of DNA, identifying a crystalline structure referred to as the DNA's backbone; a sugar phosphate molecule called "Deoxyribose" and represented in the acronym as the letter "D".

Ribose, is a simple 5-carbon molecule of monosaccharide sugar. Another form of monosaccharide sugar which you might be familiar with, would be glucose (blood sugar), or fructose (fruit sugar), which are 6-carbon sugars. Sucrose, or common table sugar is actually a disaccharide composed of two molecules of either glucose or fructose bonded together with a shared atom of oxygen. The "Deoxy" part refers to the addition of a second hydroxyl group (OH radical) to a ribose sugar molecule which would have only a single OH radical. The combined form then would be Deoxyribose.

The nucleic acid part of DNA, represented by the letters "NA" is comprised of four different amino acids, Adenine (A), Cytosine (C), Guanine (G), and Thymine (T). There are actually 20 different forms of "amino acid" molecules which are all based on the amine molecule. The amine molecule consists of an ammonia molecule and a methane molecule bonded together, and is a naturally occurring chemical substance, which along with water is an essential ingredient of all living organisms.

Exactly how all of this Deoxyribose sugar and Nucleic amino acid profusion comes together to form the structural edifice of the DNA molecule was a rather difficult puzzle to solve, but on April 25, 1953, two scientists James Watson and Francis Crick, announced to the world that they had accomplished the feat. Based on Rosalind Franklin's deoxyribose backbone, and Linus Paulings helical structure of polypeptide chains (long strains of protein molecules) and hydrogen bonds, Watson and Crick unveiled their model of a double helix DNA configuration. Their model resembled a helical staircase arrangement, where pairs of amino acids joined by hydrogen bonds at the middle and connected with peptide bonds to the deoxyribonucleic backbone, were stacked one on top of the other, coiling around to form the DNA molecule consisting of literally millions of stair steps, or as they are referred to in chemical terms "nucleotides".

Well there you have it. If I have done a fairly effective job as writer, and you as reader have been able to follow along and comprehend this pretty high level summary of DNA in historical and chemical terms, the next time you bump into this little three letter acronym you aught to be pretty well versed in just what it stands for. If you are intrigued and want to learn more, you can obtain a more in depth understanding of DNA and its implications, in the two books identified in the reference section below.



REFERENCES AND ADDITIONAL READING:

James D. Watson, DNA The Secret of Life, Random House, New York, 2003

Frank H. Stephenson, DNA - how the biotech revolution is changing the way we fight disease, Promethius Books, New York, 2007

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