3G3+Bio+Essay+by+Liow+Wei+Yuan,+Edward+Low

Wei Yuan: Red Edward: Blue

DNA is **d**eoxyribo**n**ucleic **a**cid. DNA’s main function is carrying the genetic information needed for all processes within cells.

DNA is composed mainly of nucleotides. Nucleotides are made up of a deoxyribose sugar, a phosphate group and a nitrogenous base. DNA contains four such bases: Adenine (A), thymine (T), guanine (G) and cytosine (C). There are two types of bases, purines and pyrimidines. Adenine and guanine are purines while thymine and cytosine are pyrimidines. These bases form different nucleotides, each containing a single molecule of the base, which can join together by a condensation reaction, resulting 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. Phosphodiester bonds link the nucleotides togther. The end product is a polynucleotide. DNA molecules consist of two parallel chains of such polynucleotides. The nucleotides in a strand are joined in an order that travels from either the terminal hydroxyl end to the terminal phosphate end, or vice versa. The direction of nucleotides in one strand is the opposite of that of its opposite strand, called an antiparallel arrangement. The strands are wound around each other, creating a double helix. Each base pair is rotated 36 degrees compared to the next. The bases of a strand are always joined to its opposite in purine-pyrimidine pairs which fit perfectly. Adenine always bonds with thymine and guanine always bonds with cytosine. This gives DNA a structural advantage, as it can easily separate into its separate strands when required, each strand forming a template for another strand of DNA to attach to it. This allows for easy replication of DNA. It also allows for RNA to be copied from a template strand.