3G3+bio+essay+by+Phua+Zai+Wei+Qu+Zhe+Wei+Kenneth+Lui

Phua Zai Wei. Lui Wenwei Kenneth. Qu Zhewei. Louis Ngia Jin Liang.  DNA is the abbreviation for deoxyribonucleic acid, which is the genetic material present in the cells of all living organisms. DNA is the fundamental building block for an individual's entire genetic makeup. DNA is pretty unusual in that it is about the only common molecule capable of directing its own synthesis.

The units of DNA are nucleotides, and the polymer is known as a "polynucleotide." Each nucleotide consists of a 5-carbon sugar (deoxyribose), a nitrogen containing base attached to the sugar, and a phosphate group. The sugar of DNA, carbon 2, has no hydroxyl group attached. There are four different types of nucleotides found in DNA, adenine, guanine, thymine and cytosine. Adenine and guanine are purines. Cytosine and thymine are pyrimidines.

DNA is double-stranded, the two polynucleotide stands alongside each other. The strands are antiparallel, and they run in opposite directions. The two strands are wound round each other to form a double helix and are joined together by hydrogen bonds between the bases. The bases form base pairs, like rungs of a ladder. A only binds to T, T with A, C to G and G with C. These are called complementary base pairs.

 The structure of DNA is illustrated by anti-paralle double helix, with about 10 nucleotide pairs per helical turn, with one turn being about 3.4 nm of DNA. The spiral strands are composed of a sugar phosphate backbone and attached bases, with the sugar-phosphate backbone on the outside of the helix and the bases on the inside. The backbone can be thought of as the sides of a ladder, whereas the bases in the middle form the rungs of the ladder. The structure of the DNA molecule accounts for how it can replicate itself. The molecule is able to split up and new matching bases are added in to create two new molecules. This is called semiconservative replication because each new molecule has one “old” and one “new” strand of DNA.  Each of the spiral strands is connected to a complementary strand by non-covalent hydrogen bonding between paired bases, adenine (A) with thymine (T) and guanine (G) with cytosine (C). Adenine and Thymine are connected by 2 hydrogen bonds while Guanine and Cytosine are connected by 3 hydrogen bonds.  DNA is comprised of four building blocks called bases. The building blocks are: Cytosine, Guanine, Thymine, Adenine. These are commonly referred to as C, G, T, A. It is the sequence of these building blocks that determines each person's genetic characteristics. DNA is contained in blood, semen, skin cells, tissue, organs, muscle, brain cells, bone, teeth, hair, saliva, mucus, perspiration, fingernails, urine and essentially every part of the human body. Thus it is a very useful tool to help police identify people as everyone's DNA is unique.  Embedded is a video showing the structure of a DNA molecule: media type="youtube" key="qy8dk5iS1f0" height="385" width="480"

References: <span style="color: rgb(255, 0, 221);"> www.nobelprize.org/educational_games/medicine/dna_double_helix/readmore.html www.blc.arizona.edu/Molecular_Graphics/DNA_Structure/DNA_Tutorial.HTML www.en.wikipedia.org/wiki/DNA www.accessexcellence.org/RC/VL/GG/structure.php <span style="color: rgb(13, 75, 175);">http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookDNAMOLGEN.html http://biology.clc.uc.edu/courses/bio104/dna.htm http://www.youtube.com/watch?v=qy8dk5iS1f0&feature=related http://www.dna.gov/basics/biology/ <span style="color: rgb(255, 0, 221);">