3G2+Hu+Yongda,+Loo+Zhen+Wei+and+Wang+Guan+Bo

Hu Yongda -- red Loo Zhen Wei -- green Wang Guan Bo -- blue

Deoxyribonucleic acid (DNA) is a molecule that carries genetic information, which is important for all cellular functions. Each DNA molecule consists of two parallel strands twisted around each other to form a double helix. A helix is a coiled structure like a corkscrew or a spring. A molecule of DNA is wrapped around proteins to form a single chromatin thread. During cell division, chromatin threads coil tightly into structures called chromosomes inside the cell nucleus. The basic unit of DNA is called a nucleotide which is made up of a sugar called deoxyribose  (a 5 carbon sugar), a phosphate group and a nitrogen-containing base joined together. There are four types of nitrogen-containing bases in DNA: adenine, cytosine, guanine and thymine.

Nucleic acids have the same basic structure in all organisms. Nucleic acids are long chains of similar subunits called nucleotides. These long chains are called polymers. A nucleotide is composed of three different molecules, a phosphate group, a sugar, and a nitrogen base. DNA contains a 5 carbon sugar as mention above. In DNA, the sugars are closed to form ring structures. A nucleotide’s central component is the sugar. The phosphate is attached to the number 5 carbon of the sugar and the nitrogen base is attached to the number 1 carbon of the sugar. Nucleotides are joined together into a polymer string by joining the phosphate group of one nucleotide, to the number 3 carbon of the next sugar, hence forming DNA.

In the helix, the sugar-phosphate backbone is on the outside, while the nitrogen-containing base pairs are on the inside. They form a ladder-like shape in which the sides of the ladder represent the backbone while the bases can be imagined as the rungs. Every "rung" includes a nitrogen-containing base pair. The base pair can be either an adenine-thymine pair or cytosine-guanine pair. Two intermolecular hydrogen bonds hold the adenine-thymine pair together, while the cytosine-guanine pair is bonded by three intermolecular hydrogen bonds. The length of an adenine-thymine pair is the same as that of a cytosine-guanine pair, therefore the sugar-phosphate backbone is smooth.

References (Recited due to improper citation) Nobel Prize. The Discovery of the Molecular Structure of DNA - The Double Helix. Retrieved July 9, 2009, from the Nobel Prize website: http://nobelprize.org/educational_games/medicine/dna_double_helix/readmore.html

Jrank. Deoxyribonucleic Acid (DNA) - History, Structure, Function, Replication Of Dna, The Genetic Code, Expression Of Genetic Information. Retrieved July 9, 2009, from the Jrank website: http://science.jrank.org/pages/2007/Deoxyribonucleic-Acid-DNA.html

Angelfire. DNA (Deoxyribonucleic Acid). Retrieved July 9, 2009, from the Angelfire website: http://www.angelfire.com/ks3/deoxyribonucleicacid/

Biological Sciences Initiatives. DNA Components and Structure. Retrieved July 9, 2009, from the Biological Sciences Initiatives website: http://www.colorado.edu/Outreach/BSI/pdfs/DNA_components.pdf 