DNA: Difference between revisions

<scene name='User:Adithya_Sagar/Sandbox_DNA/B-dna/4'>DNA</scene> consists of two polynucleotide chains, <scene name='DNA/B-dna/16'>twisted around each other to form a double helix</scene>. The <scene name='DNA/B-dna/29'>nucleotide</scene> in DNA is composed of of a <scene name='DNA/B-dna/36'>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='DNA/B-dna/22'>Adenine (A)</scene> and <scene name='DNA/B-dna/23'>Guanine (G)</scene> and the two single-ringed pyrimidine bases <scene name='DNA/B-dna/28'>Thymine (T)</scene> and <scene name='DNA/B-dna/27'>Cytosine (C)</scene>. Hydrogen atoms on some nitrogen and oxygen atom can undergo tautomeric shifts. The nitrogen atoms that are involved in forming tautomer appear as amino or imino groups and the oxygen atoms are either in keto or enol forms. Using an isolate thymine to illustrate the <scene name='DNA/Thymine_enol/1'>imino/enol tautomer</scene> and the <scene name='DNA/Thymine_keto/2'>amino/keto tautomer</scene>. There is a preference for the amino and keto forms which is very crucial for the biological functioning of DNA as it provides a <scene name='DNA/Amino-glycosidic/1'>ring nitrogen capable of forming a glycosidic bond</scene> with the deoxyribose and it leads to the specificity of hydrogen bonding in base pairing and thus complementarity of the chains.<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 imino nitrogen can only serve as a donating atom in hydrogen bonding, but the amino nitrogen can also serve as a receiving atom. Each nucleotide in a DNA chain is linked to another via <scene name='DNA/Diester/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>