3G3+Bio+Essay+by+Ce+Shun,+Zher+Yin,+Chenrui

Foo Ce Shun - Green Tan Zher Yin - Red Elias Tan - Blue Ang Chenrui - Brown

Deoxyribonucleic acid, or DNA for short, is a molecule that contains genetic information. These information carry the instructions that make every single living organism the planet and enable cellular functions to occur. DNA is a type of nucleic acid due to its weak acidic properties and are polymers, composed of monomers called nucleotides.
 * __ Introduction __**

Such nucleotides consists of three parts, a phosphoric acid, a pentose sugar and a nitrogenous base. These nucleotides can join together by a condensation reaction between the phosphate group of one nucleotide and the hydroxyl group on carbon 3 of the sugar of the other nucleotide, which would result in the removal of water. Phosphodiester bonds then link the nucleotides together. The bases do not take part in the polymerisation, so there is a sugar-phosphatebackbone with the bases extending off it. Due to the double stranded DNA, there are two polynucleotide standing alongside each other, and are antiparallel. The two strands are wound round each other to form a double helix being joined together by hydrogen bonds between the bases which would therefore form base paris like rungs of a ladder. These base pairs are very specific, with A binding to T and T bidnign to A and C binding to G and G binding to C. These pairs are called complementary base pairs. Deoxyribonucleic acid or DNA is a molecule that carries genetic information. Each DNA molecule consists of two parallel strands twisted around each other to form a double helix. A double helix is a structure that coils around itself, as shown in the diagram on the bottom right of the page. These molecules are wrapped around proteins, forming chromatin threads. The chromatin threads themselves coil up into structures called chromosomes inside the cell nucleus of each cell.
 * __DNA structure__**

The monomer of DNA is called nucleotides. Each nucleotide has a 5-carbon sugar, which is deoxyribose, a nitrogenous base, and a phosphoric acid component. There are four types of nucleotides in DNAs: adenine, guanine, cytosine and thymine. Adenine and guanine are purines, cytosine and thymine are pyrimidines. Purines are larger than pyrimidines. These nucleotides can combine and form long chains called polynucleotides. To form a DNA molecule, two parallel polynucleotide chains must to put together and run in opposite directions.
 * __ Basic units of DNA __**

**__ References: __**
 * Lam, P. K. (2007). //Biology Matters//. Singapore: Marshall Cavendish Education.
 * Open-source, (2009). DNA. Retrieved July 12, 2009, from Wikipedia, the free encyclopedia Web site: http://en.wikipedia.org/wiki/DNA