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Berger 1 Sarah Berger Mr. Miller 9, Biology P2 8 December 2010 DNA: Our Code to Life A baby is born. A girl grows up. Neither one of them is an exact copy of one parent. They have traits that both their mothers and fathers have – brown eyes, blonde hair, and good eye sight. Why is this? One seemingly simple thing is the answer to that question: DNA. DNA, or deoxyribonucleic acid is a very complex molecule that resides in every cell of the body. In pictures of cells, you see a few “X’s” in the nucleus. If those were to unravel, they would make up several six-footlong strands of DNA. Some articles state that Watson and Crick were the first to discover our deoxyribonucleic acid. Those facts have been proved incorrect. The first true discovery of DNA was by a man named Friedrich Miescher. He was born in Basel, Germany in 1844. Miescher later moved to Tübingen, Germany, where he made his great discovery. Miescher had always been intrigued with nuclei. As he was studying them, he found something very peculiar. At the time, Miescher did not have very much easy access to cells. Luckily, a hospital agreed to give him bloody bandages from the patients. In the beginning of his experiments, it was very hard to separate the blood from the bandage without damaging the cells. After hard work, Miescher created a sodium sulfate substance that would filter the blood cells into a Berger 2 beaker. He was then able to separate the nuclei from the cytoplasm. Once that happened, Miescher applied an alkaline extraction then acidified the nuclei which allowed him to see clearly the DNA. He did not know exactly what its function was, but his discovery has inspired many scientists and the name of two universities. Earlier referenced, Watson and Crick, Made a very large discovery to DNA. They had studied it for a long time, but never really made any discoveries. After attending Rosalind Franklin’s lecture in Cambridge, Watson had some ideas about the shape of a DNA molecule. He built a model with Crick, but it was no good. They thought long and hard about this structure, and later proposed that it was a helix with two nucleotide strands. That led to the realization of the technical shape of the double helix (DNA). Another person who got us one step closer to discovering the purpose of DNA was Gregor Mendel. He almost solely discovered how heredity works. Heredity, for example is when genes are passed from generation to generation. In the early nineteenth century, it was thought that traits were “blended.” Blending was combining the traits of the parents. For example, if one parent had long legs and the other had short, you would have medium length legs. Mendel knew that was not possible. That is why he thought of heredity. Because it would take too long to experiment this component of DNA on humans, Mendel used pea plants. It also turned out he used those plants because they had easily measurable traits (shape, size, and color). He started his Berger 3 experiment in the spring of 1856; Mendel knew he would need a myriad of peas, so he grew more than 24,000 plants. In Mendel’s first experiment, he cross-pollinated round, yellow peas with wrinkly, green ones (Rubin). He found that their offspring were all yellow and smooth. Mendel learned from this that there are two kinds of traits - dominant and recessive. In this case, the dominant traits are the yellow color and the round shape since they show up at the expense of the green color and the wrinkly shape. He also learned that the inheritance of each trait is determined by "units" or "factors" - now called genes (Rubin). Through this, Mendel discovered alleles –alternate forms of a gene. To have a dominant trait, you need to have at least one dominant allele. To have a recessive trait, one must have two recessive alleles. Without the components that make up deoxyribonucleic acid, we would not have genes, not to mention peas. The four main components in DNA are guanine (g), cytosine (c), thymine (t), and adenine (a). Cytosine and guanine always combine; those base pairs help hold the two sugar phosphate backbones (shown in picture to the right). Adenine and thymine also always combine to help hold the backbones together. As discovered in investigation one, every molecule is made of two or more atoms. In the case of the four acids, those Berger 4 atoms all happen to be: carbon, hydrogen, nitrogen, and oxygen. The chemical formula for guanine is C5H5N5O; Cytosine’s is C4H5N3O, adenine’s formula is C5H5N5, and thymine’s is C5H6N2O2. They are all pretty similar. It is difficult to comprehend the simplicity of our structure. Four elements and acids can decide whether we have brown eyes or blue. It can decide whether we are good at building things or playing violin. DNA is a blueprint, a building block for life. All the a’s, t’s, g’s, and c’s are arranged in a certain way. That is called a sequence. Everybody’s DNA sequence is different, even if it is just one letter different (which is possible but not hardly plausible). The sequence is the blueprint. It tells the body exactly what has to happen. Different parts of the sequence contain different genes. Every human has something in common. We all have around twenty-thousand genes. There are two kinds of genes, recessive and dominant. Recessive genes are the least likely to occur in a cell. Dominant are the most common genes and every living thing has at least one. There are actually diseases that occur when a being has too many recessive genes. For example some recessive genes are blonde hair and green eyes, albinism, and attached earlobes. When DNA is coiled up and scrunched down, it takes chromosome form. Those are found in the nuclei of eukaryotic cells. DNA does not only determine the shape of one’s ears. It decides what gender that organism is. Every animal [including humans] has at least one “X” chromosome. The way gender is determined is Berger 5 whether an animal has a “Y” chromosome or not. If it has two X’s, it’s female. If it has an X and a Y, it’s a male. In birth, the mother gives one of her X chromosomes. The father can give either his X or Y chromosome. Recapping the earlier stated sentence, if he gives an X, it will be a girl. If he gives a Y, it will be a boy. They say it’s a woman’s job to bear a boy, but it is really up to the man. Even the smallest things are different, including chromosomes. A Y chromosome is comparatively smaller than an X [as displayed in the above picture]. Y’s have 78 genes whereas X’s have 1,098. DNA is the basis for cloning. You may have heard of the sheep, Dolly. She was the first large mammal to ever be cloned. It took 277 tries to clone this animal, which made the experiment ethically questionable. First, the scientists took a cell from a Finn Dorset white sheep’s udder. They then removed the nucleus from it. The scientists had also previously taken an unfertilized egg from a black-faced sheep and removed its nucleus. They fused the udder cell’s nucleus into the unfertilized egg and implanted it into a surrogate mother. After around 150 days, Dolly the lamb was born. She was just about an exact copy of the Finn Dorset white sheep. The only difference was that the mitochondria in her cells were from the egg donor’s DNA. The reason Dolly was almost an exact copy of the original white sheep is because of DNA. She had the same deoxyribonucleic acid because it was the in the white sheep’s nucleus. I can take away from this project not only what DNA is made of, but why it is so important. If we didn’t have it, our bodies wouldn’t know how tall to grow or how much hair Berger 6 we should have on our heads. We probably wouldn’t even have bodies. We wouldn’t be alive because in order to live, animals have to reproduce. How are we to reproduce without this wonderful thing called DNA? Berger 7 Works Cited "Cloning Dolly the Sheep - AnimalResearch.info." Home - AnimalResearch.info. Web. 04 Dec. 2010. <http://www.animalresearch.info/en/medical/timeline/Dolly>. "Dominant & Recessive Genes." Blinn College. Web. 04 Dec. 2010. <http://www.blinn.edu/socialscience/ldthomas/feldman/handouts/0203hand.htm>. Fetzer, Scott. "DNA." World Book. 2005. Print. "The First Discovery of DNA » American Scientist." American Scientist Online. Web. 04 Dec. 2010. <http://www.americanscientist.org/issues/page2/the-first-discovery-of-dna>. Fogel, Daniel. "Gregor Mendel." World Book. 2007. Print. "Friedrich Miescher." Wikipedia, the Free Encyclopedia. Web. 04 Dec. 2010. <http://en.wikipedia.org/wiki/Friedrich_Miescher>. "A Science Odyssey: People and Discoveries: Watson and Crick Describe Structure of DNA." PBS: Public Broadcasting Service. Web. 04 Dec. 2010. <http://www.pbs.org/wgbh/aso/databank/entries/do53dn.html>. Roger, Klare. Gregor Mendel. New York: Enslow 1978. Trubin, Julian. "Gregor Mendel: The Pea Plant Experiment." The Orchid Grower: A Juvenile Science Adventure Novel. Web. 04 Dec. 2010. <http://www.juliantrubin.com/bigten/mendelexperiments.html>. "X and Y Chromosomes." D.G. Leahy - The New Universal Consciousness. Web. 04 Dec. 2010. <http://dgleahy.com/dgl/p34.html>.