3G2+Bio+Essay+by+Wesley+Leong+(11),+Lim+Jun+Rong+(12),+Kevin+Tan+(22),+Teoh+Zhihao+(24)

Wesley Leong - red Lim Jun Rong - blue Kevin Tan - yellow Teoh Zhihao - green   Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions used in the development and functioning of all living organism. A DNA molecule consists of two parallel strands twisted around each other, forming a double helix and it wraps around protein to form a chromatin thread. DNA has a basic unit called a nucleotide which comprises deoxyribose, a phosphate group and a nitrogen containing base which all are joined together. There are four main bases, namely adenine, thymine, guanine, and cytosine. Three of these bases in sequence form a genetic codon. Codons are vital to protein synthesis as their position determines the sequence at which they are transcripted or translated; the transcription and translation of codons in DNA does not encompass the overlapping reading of codons, meaning that for any given anomaly in the genetic sequence, the protein might not even be able to synthesize.  

The structure of DNA is a right handed double helix, with about 10 nucleotide pairs per helical turn. Each spiral strand, composed of a sugar phosphate backbone and attached bases, is connected to a complementary strand by hydrogen bonding (non- covalent) between paired bases, adenine (A) with thymine (T) and guanine (G) with cytosine (C). Adenine and thymine are connected by two hydrogen bonds (non-covalent) while guanine and cytosine are connected by three.  Nucleotides act as building blocks of DNA as nitrogen-containing bases, deoxyribose sugars and phosphate groups can combine to form 4 different variations of nucleotide molecules. These nucleotides then can be joined together to form long chains called polynucleotide. Each gene can be made up of a sequence of nucleotides whic h can vary, resulting in many different genes. The order, or sequence, of these bases determines the information available for building and maintaining an organism. An important property of DNA is that it can replicate and make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases which proved to be useful in cell division as each new cell needs to have an exact copy of the DNA present in the old cell.  Deoxyribose is essentially a monosaccharide containing five carbon atoms and contains an aldehyde functional group in its linear structure. This is derived by ribose, where an hydroxyl group is replaced with hydrogen, resulting in a net loss of an oxygen atom, hence the name “deoxyribose”. A phosphate group is attached to the sugar molecule in place of the OH- group on the 5’ carbon, transforming into a nucleotide.

 (SCQ, 2009)

Bibliography


<span style="color: rgb(0, 0, 255);">Lam Peng Kwan (2000). GCE 'O' Level Biology Matters. Marshall Cavendish Education Saenger, Wolfram (1984). //Principles of Nucleic Acid Structure//. New York: Springer-Verlag. <span style="color: rgb(255, 255, 0);">http://www.accessexcellence.org/RC/VL/GG/dna_molecule.php <span style="color: rgb(0, 0, 255);"> <span style="color: rgb(0, 0, 255);">http://www.scq.ubc.ca/ http://ghr.nlm.nih.gov/handbook