3G2+and+G3+Bio+DNA+Essay+by+Kenny+Loke,+Bernard+Chu,+See+Jie+Xun,+Liu+Guo+Sheng

DNA, or deoxyribonucleic acid, has three main parts to it: a phosphoric acid, a 5-carbon or pentose sugar, and a nitrogenous base. DNA is double-stranded, so there are two polynucleotide strands alongside each other. These strands are anti-parallel, which means they run in opposite directions, and they are wound around each other to form a double helix. The sugars and phosphate groups act as the back bone of the DNA. The strands are joined by hydrogen bonds between the bases, which form base pairs like the rungs of a ladder. The base pairs are specific, with adenine (A) only binding to thymine (T), and Cytosine (C) only binding to guanine (G). However, RNA uses uracil (U) in place of thymine.
 * Essay describing DNA structure**

As mentioned above, DNA consists of two long polymers of nucleotides. Nucleotides are molecules that join together to form the basic structural units of DNA and RNA. Nucleotides comprise deoxyribose, a nitrogen base, and a phosphate group. Different nitrogenous bases can combine with the deoxyribose and phosphates to form different types of nucleotide molecules. Phosphodiester bonds link the nucleotides together to create polynucleotides.

Three nucleotides bases form a base triplet. There are 4 nitrogenous bases and they are arranged in triplets, thus there are 64 possible combinations of base triplets. However, there are only 20 amino acids that can be coded, and therefore there are special cases when more than one base triplet can code for the same amino acid. Therefore, the whole polynucleotide chain of the anti-sense strand of a DNA molecule can code for a protein, and this forms the genetic code which specifies the sequence of the amino acids within proteins.

Within cells, DNA is organized into X-shaped structures called chromosomes. These chromosomes are duplicated before cells divide, in a process called DNA replication. Most organisms store their DNA inside the cell nucleus and some of their DNA in the mitochondria and chloroplasts.

Liu Guo Sheng – Orange See Jie Xun – Red Kenny Loke – Blue Bernard Chu - Green