Bio+Essay+By+BenToh,+Xue+Quan,+Jiang+Shen,+Jun+Hean+3G3

Xue Quan (Red)

Ang Jun Hean (Pink)
 DNA stands for deoxyribonucleic acid and it is a nucleic acid. DNA is a polymer, and composes of monomers called nucleotides. The nucleotides have three parts to them: a phosphoric acid, a 5-carbon or pentose sugar(carbon 2 with hydroxyl group attached, known as deoxyribose), a nitrogenous base. There are four types of nitrogen-containing bases in DNA. They are called adenine (A), cytosine (C), guanine (G), and thymine (t). The nitrogen-containing bases, deoxyribose sugars and phosphate groups can combine to form four different nucleotide. Nucleotides can join together by a condensation reaction which results in the removal of water between the phosphate group of one nucleotide and the hydroxyl group on carbon 3 of the sugar of the other nucleotide. The joined nucleotides are called polynucleotides. Phosphodiester bonds link the nucleotides together. Illustration of an uncoiled DNA molecule: 

 Illustration of a coiled DNA molecule:  There are a few main features of the three-dimensional structure of DNA. DNA is double-stranded, meaning that there are two polynucleotide standing alongside each other. Also, the strands of a DNA are antiparallel, meaning that they 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 therefore form base pairs. A uncoiled DNA molecule resembles a ladder, while the twists of the coiled DNA molecule resemble a spiral staircase. The base pairs are specific.I i.e. A only binds to T (and T with A), and C only binds to G (and G with C). These base pairs are called complementary base pairs, i.e. Adenine and thymine are complementary bases, same for cytosine and guanine.

In each DNA molecule, the ratios of Adenine to thymine (A:T), and the cytosine to guanine (C:G), are 1:1.  ===<span style="color: rgb(255, 0, 255);">In geometry a double helix typically consists of two congruent helices with the same axis, differing by a translation along the axis. It is also based on this structure that the DNA molecule is based upon. ===

<span style="color: rgb(255, 0, 255);">
===<span style="color: rgb(255, 0, 255);">The famous biologists Watson and Crick took the above pieces of research and decided that the only structure that could fit the data they had on DNA was the structure of the double helix. ===

<span style="color: rgb(255, 0, 255);">There are seven important features of the double helix:

 * ===<span style="color: rgb(255, 0, 255);">The double helix consists of two poly nucleotides. ===
 * ===<span style="color: rgb(255, 0, 255);">The nitrogenous bases are on the inside of the helix with the sugar phosphate backbone on the outside. ===
 * ===<span style="color: rgb(255, 0, 255);">The bases of the two complementary poly nucleotides are bonded by hydrogen bonding. ===
 * ===<span style="color: rgb(255, 0, 255);">The double helix turns every ten base pairs. ===
 * ===<span style="color: rgb(255, 0, 255);">The two poly nucleotide strands are anti parallel, that is one strand runs one direction and the other strand runs the opposite direction. ===
 * ===<span style="color: rgb(255, 0, 255);">The double helix contains two different grooves, a major and a minor groove. ===
 * ===<span style="color: rgb(255, 0, 255);">The double helix is right handed, meaning that if the double helix was a spiral staircase, if you climbed up it, the banister in reference to the spiral staircase structure referencing to the sugar phosphate backbone would be on your right hand side. ===

Read more: []

<span style="color: rgb(0, 0, 255); font-family: 'Arial Black',Gadget,sans-serif;">

References: <span style="color: rgb(0, 0, 0); font-family: Tahoma; font-size: 12px; line-height: normal; white-space: pre;">[|http://www.biosulf.org/1/images/nucleotides.gif]

[|http://www.chemguide.co.uk/organicprops/aminoacids/doublehelix.gif]

__<span style="color: rgb(0, 0, 255);">www.**doublehelix**glassworks.com/

www.massey.ac.nz/~wwbioch/**DNA**/**DNA**make/framset.htm

www.colorado.edu/Outreach/BSI/pdfs/**DNA**_**components**.pdf __