DNA is a double-stranded nucleic acid that contains the genetic information for cell growth, division, and function. DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Most DNA is located in the cell nucleus but a small amount of DNA can also be found in the mitochondria .The information in DNA is stored as a code made up of four nitrogen bases which are adenine (A), guanine (G), cytosine (C), and thymine (T). these nitrogen bases are bind with each other through hydrogen bond.  History of DNA research
Before a cell can divide, it must duplicate all its DNA. In eukaryotes, this occurs during S phase of the cell cycle. The Biochemical Reactions
* DNA replication begins with the "unzipping" of the parent molecule as the hydrogen bonds between the base pairs are broken. * Once exposed, the sequence of bases on each of the separated strands serves as a template to guide the insertion of a complementary set of bases on the strand being synthesized. * The new strands are assembled from deoxynucleoside triphosphates. * Each incoming nucleotide is covalently linked to the "free" 3' carbon atom on the pentose (figure) as * the second and third phosphates are removed together as a molecule. * The nucleotides are assembled in the order that complements the order of bases on the strand serving as the template. * Thus each C on the template guides the insertion of a G on the new strand, each G a C, and so on. * When the process is complete, two DNA molecules have been formed identical to each other and to the parent molecule.  Significance
* DNA is the building block of all organisms. Looking for mutations in DNA helps to uncover the reasons why some people develop certain diseases while others remain disease free. The discovery and study of DNA helps physicians and researchers discover how to test for and treat diseases. Understanding DNA also...
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