DNA: Difference between revisions

DNA consists of two polynucleotide chains, <scene name='DNA/B-dna/16'>twisted around each other to form a double helix</scene>. The nucleotide in DNA is composed of of a <scene name='User:Adithya_Sagar/Workbench_newDNA/B-dna/19'>5' phosphorylated sugar</scene> which is a beta-D-2'- deoxyribose and a purine or a pyrimidine <scene name='User:Adithya_Sagar/Workbench_newDNA/B-dna/18'>base</scene>.  The four types of bases are the two double ringed purine base <scene name='User:Adithya_Sagar/Workbench_newDNA/B-dna/1'>Adenine (A)</scene> and <scene name='User:Adithya_Sagar/Workbench_newDNA/B-dna/2'>Guanine (G)</scene> and the two single pyrimidine bases <scene name='User:Adithya_Sagar/Workbench_newDNA/B-dna/6'>Thymine (T)</scene> and <scene name='User:Adithya_Sagar/Workbench_newDNA/B-dna/5'>Cytosine (C)</scene>.Each nucleotide in a DNA chain is linked to another via <scene name='User:Adithya_Sagar/Workbench/Retest/B-dna/2'>3',5' phosphodiester bond</scene>. There are four nucleotides in DNA.  The sugar-phosphate backbone of the DNA is very regular owing to the phosphodiester linkage whereas the ordering of bases is highly irregular.<ref name='Watson'> Watson, James D, Nancy H. Hopkins, Jeffrey W. Roberts, Joan Argetsinger Steitz, Alan M.Weiner ''Molecular Biology of Gene'' (4th ed.). The Benjamin/Cummings Publishing Company Inc.pp. 239-249. ISBN 0-8053-9612-8</ref>

The two chains in a DNA are joined by hydrogen bonds between specific bases. Adenine forms a base pairs with thymine and guanine with cytosine. This specific base pairing between <scene name='User:Adithya_Sagar/Workbench_newDNA/B-dna/14'>Adenine-Thymine</scene> and <scene name='User:Adithya_Sagar/Workbench_newDNA/B-dna/15'>Guanine-Cytosine</scene> is known as Watson-Crick base pairing.  The specificity of hydrogen bonding between bases leads to complementarity in the sequence of nucleotides in the two chains. Thus in a strand of DNA the content of adenine is equal to that of thymine  and the guanine content is equal to the cytosine content.  In general DNA with higher GC content is more stable than the one with higher AT content owing to the stabilization due to base stacking interactions.