PAGE PAGE 1 The Structure of DNA
The Structure of DNADNA, or deoxyribonucleic acid, is the hereditary material in humans and almostall other organisms. Nearly every cell in a person's body has the same DNA. Most DNAis located in the cell nucleus (it is called nuclear DNA), but a small amount of DNAcan also be found in the mitochondria (U.S. National Library of Medicine, 2009). ADNA molecule consists of two chains of nucleotides (polymers of nucleic acid eachcomposed of a phosphate, a five carbon sugar, and a nitrogenous base) that spiral to formthe double helix shape. The nucleotides that forms the DNA structure are organized sotheir sugar-phosphate components face the outside and form ...view middle of the document...
James D. Watson and Francis Crickdetermined the structure of DNA in 1953, using the X-ray crystallography work ofRosalind Franklin that indicated DNA had a helical structure (i.e., shaped like acorkscrew). Their double-helix model had two strands of DNA with the nucleotidespointing inward, each matching a complementary nucleotide on the other strand to formwhat looks like rungs on a twisted ladder (Miko, 2008). This structure showed thatgenetic information exists in the sequence of nucleotides on each strand of DNA. Thestructure also suggested a simple method for duplication: if the strands are separated, newpartner strands can be reconstructed for each based on the sequence of the old strand.Meiosis is the process of making a cell that has the same number of chromosomesas the parents. In order to keep the same number, they each make gametes which havehalf his or her own number of chromosomes. When one gamete, sperm, fertilizes theother gamete, the egg, they join their number of chromosomes together to make anoffspring with the same number as the parents have (Miko, 2008). If they did not do thisby meiosis, then very soon, animals could potentially have large numbers ofchromosomes. Basically the responsibility of passing on genetic information todeveloping cells and to future generations lies with the chromosomes. The majorfunction of the chromosomes is carried out with relatively few errors largely because oftheir structure. The condensed nature of chromosomes allows DNA to be packed intocompact form that is easier for the cell to manipulate during mitosis and meiosis(Strachan, 2009).The principles of heredity all started with an Augustinian monk by the name ofGregor Mendel in 1865. Mendel did a great deal of experimentation with flowers toprove his theories. Mendel discovered that by crossing white flower and purple flowerplants, the result was not a hybrid offspring. Rather than being a mix of the two, theoffspring was purple flowered. He then conceived the idea of heredity units, which hecalled "factors," one which is a recessive characteristic and the other domina...
