3B1+Bio+DNA+Essay+by+Chow+Cheng+Yong,+Justin+Teh,+Zhu+Fang+Chen,+Soh+Hong+Woon

= = =Zhu Fang Chen =

Soh Hong Woon
-- DNA stands for deoxyribonucleic acid and it stores the genetic information used for development of all living organisms. The basic building blocks of a DNA are nucleotides which consist of a sugar (deoxyribose) bound on one side to a phosphate group and another side to nitrogenous base. The sugar and phosphate forms the phosphate backbone which the DNA will then be built on. The two different nitrogenous bases a sugar can bind on to are purine (adenine and guanine) and pyrimidine (thymine and cytosine). There is only one way the nitrogenous base can be paired – adenine and thymine, guanine and cytosine, but there are millions of sequences the DNA strands can form. = = =The purines bind only with pyrimidines and vice versa. Purines cannot bind with purines and pyrimidines cannot bind with pyrimidines. The reason can be explained by looking at the structure of the nitrogenous bases. Below are cytosine and guanine. = = = = = = = =Based on the structure, if two purines are put together they will not fit between the sugar-phosphate backbone of regular DNA. On the other hand, if two pyrimidines are put together, they will be too far away to form strong hydrogen bonds when attached to the sugar phosphate backbone. But when purines and pyrimidines are put together, they fit perfectly. = =The nitrogenous bases are important not because all the combinations and sequences of the bases in the DNA are responsible for the different codons in protein synthesis. In a sense, they are ‘symbols’ that make up the ‘code’ of DNA. Also, they are important in holding the structure of DNA. The hydrogen bonds between each pair of bases provide stability for the structure of DNA. = = = = = =The sugar in DNA is deoxyribose- this form of the sugar contains one less oxygen atom. Deoxyribose sugar is a monosaccharide with five carbon atoms an aldehyde functional group in its linear structure. The deoxyribose sugar is also called deoxyribofuranose because it is a five membered ring with four carbon atoms and an atom of oxygen. = =Deoxyribose plays an important part in Biology. One important derivative are deoxyribose with phosphate groups attached at their 5th position. Mono, di, triphosphate, and 3-5 cyclic monophosphates are important. There are also important diphosphate dimers called coenzymes which are formed when purines and pyrimidines form an important class of compounds with ribose and deoxyribose. When these purine and pyrimidine derivatives are coupled to a ribose sugar, they are called nucleosides  = =<span style="background-color: rgb(255, 255, 255); font-family: Arial,Helvetica,sans-serif; color: rgb(255, 0, 237); font-size: 80%;"> = =<span style="background-color: rgb(255, 255, 255); font-family: Arial,Helvetica,sans-serif; color: rgb(255, 0, 237); font-size: 80%;"> = =<span style="background-color: rgb(255, 255, 255); font-family: Arial,Helvetica,sans-serif; color: rgb(255, 0, 237); font-size: 80%;">In the phosphoric acid component of DNA, nucleosides are converted to nucleotide by attachment of a phosphoric acid group to the 5' Carbon of the ribose sugar. We can call this attachment as 3'-5 ' phosphodiester bond. Phosphate group is attached by phosphodiester bond. P hosphodiester bonds, which make up the backbone of the strands of DNA, are the strong covalent bonds between the phosphorus atom in a phosphate group and two other molecules over two ester bonds. An ester is an organic compound formed from an alcohol and acid. The alcohol group is the 5 ' hydroxyl of the sugar and the acid is phosphoric acid. Up to three individual phosphate groups can be attached in series giving a nucleotide monophosphate (NMP), nucleotide diphosphate (NDP) and nucleotide triphosphate (NTP). =

sources: http://www.massey.ac.nz/~wwbioch/DNA/DS-DNA/framset.htm http://www.massey.ac.nz/~wwbioch/DNA/DNAmake/framset.htm http://www.blc.arizona.edu/Molecular_Graphics/DNA_Structure/DNA_Tutorial.HTML#Components http://en.wikipedia.org/wiki/Deoxyribose http://en.wikipedia.org/wiki/Nucleobase http://en.wikipedia.org/wiki/Nucleotide http://en.wikipedia.org/wiki/Purine http://en.wikipedia.org/wiki/Pyrimidine