3S2+Bio+Essay+by+Yong+Keat,+Jie+Shun,+Sean

Group Members

 * Sean Lee Shi-Zhe 3S212
 * Poh Yong Keat 3S219
 * Teoh Jie Shun 3S230

Essay
DNA, known as Deoxyribonucleic Acid, is a molecule that carries  genetic information and it can be found in the nucleus of almost every cell in your body .They are polymers (long chains), composed of many monomers called nucleotides. Nucleotides are made up of a phosphoric acid (phosphate group), a pentose or 5-carbon sugar, which is called ribose in RNA or deoxyribose in DNA and a nitrogenous base. There are five different types of organic bases - Adenine, Cytosine, Guanine, Thymine (DNA only) and Uracil (RNA only). These organic bases are bascially fall into 2 groups, purines (two rings of carbon and nitrogen atoms) - Adenine and Guanine; and pyrimidines (a single ring of carbon and nitrogen atoms) - Cytosine, Thymine and Uracil. Nu cleotides can be joined together form polynucleotides, through condensation reactions (removal of water) between the phosphate group of one nucleotide and the hydr oxyl group on carbon 3 of the sugar of the other nucleotide, thus forming a sugar-phosphate backbone with the nitrogen-containing bases extending from it, since these bases do not take part in the polymerisation ( reaction of small molecules together to form three-dimensional networks or polymer chains). Phosphodiester bonds link the nucleotides together. When the nucleotides are put together, they form DNA molecules. The DNA is double-stranded (2 long chains of polynucleotides) that are anti-parallel and wind around each other to form a double helix. The 2 strands join together by hydrogen bonds between the nitrogenous bases of each nucleotide, thus forming base pairs, like rungs of a ladder. Base pairs have specific binding, also being known as complimentary base pairs. Adenine only binds to Thymine, whereas Cytosine only binds to Guanine. The DNA has two essential functions, replication and expression. Replication meaning the DNA together with its genes must be copies at each occasion of cell division while expression mans the genes on the DNA each controls/codes a particular protein.