Nucleic Acid Chemistry

BIOC 2580 Final Exam Notes 3. Nucleic Acids Structure • Linear polymers of nucleotides connected via phosphodiester bonds • Nucleotide: repeating unit consisting of sugar, base and phosphate group  2 types of nucleic acid sugars: ribose, deoxyribose  4 different bases: cytosine, thymine (uracil), adenine, guanine • Backbone is sugar linked together by phosphates  Called sugar phosphate backbone • Bases are linked to sugars The Bases Numbering Pyrimidine Bases • Single ring bases • Cytosine, thymine (5-methyluracil) and uracil (RNA) Tautomers • Tautomers: isomers which differ only in positions of protons (and double bonds)  Skeleton remains unchanged • Nucleotide bases can exists in 2 or more tautomeric forms depending on pH Tautomeric Forms of Cytosine • OH group undergoes keto/enol tautomerism • NH 2roup undergoes amino/imino tautomerism • amino + keto form predominates (middle) Purine Bases • 2 ring bases  Fused bicycle heterocycle  4 N atoms, 5 C atoms • Adenine and guanine Sugars • RNA contains D-ribose • DNA contains D-2-deoxyribose  OH on C-2 is replaced with an H • Both sugars are in β – furanose (5 membered) form Nucleosides • Nucleoside = Base + sugar