BCHM 4116 1st Edition Lecture 2 Outline of Last Lecture I Biochemistry 4116 Overview II The Central Dogma Challenging the Central Dogma Outline of Current Lecture III Structural basis of genetic material Nucleic acids A DNA vs RNA IV Purine and Pyrimidine Bases a Keto enol tautomeric shifts V DNA better suited as genetic material Current Lecture Structural Basis of Genetic Material DNA vs RNA DNA 1 Four bases make up DNA a A adenine b T thymine c C cytosine d G guanine 2 deoxy DNA doesn t have a hydroxyl group OH at the 2 position on the sugar 3 DNA is a polymer of nucleotides linked together by phosphodiester bonds 4 Double stranded RNA 1 Four bases make up RNA a A adenine b U uracil U replaces T in RNA c C cytosine These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute d e f g G guanine RNA has a hydroxyl OH on the 2 position on the sugar RNA is a polymer of nucleotides linked together by phosphodiester bonds Single stranded Purine and Pyrimidine Bases Purines 1 5 member imidazole ring fused with a pyrimidine aromatic 2 There are 2 purines a Adenine A b Guanine G Pyrimidine 1 6 member aromatic ring 2 There are 3 pyrimidines a Cytosine C b Uracil U c Thymine T 3 The two nitrogen s in a pyrimidine are separated by a carbonyl Keto Enol Tautomeric shifts Bases can undergo keto enol tautomeric shifts Keto double bond linking the oxygen to carbon Enol alcohol group connected to carbon This shift results in the bases ability to hydrogen bond Quantifying Nucleic Acids Measure absorbance at 260 nm UV light due to their aromaticity Putting it together Both DNA and RNA molecules are made up of a sugar and a base A sugar and base are linked together by a N glycosidic bond The 1 position on a sugar is linked to a nitrogen atom on a base purine pyrimidine A sugar and based connected through an N glycosidic bond is called a nucleoside Two nucleosides sugar base are joined together through a phosphodiester bond Notice that it is a di ester bond This linkage results in two esters forming at the 5 and 3 positions of the sugar When a phosphate group is added to a nucleoside it is called a nucleotide A nucleotide is a nucleoside plus a phosphate group Hence DNA and RNA molecules are polymers of nucleotides DNA and RNA is always read from the 5 3 unless otherwise stated Why is DNA better suited as genetic material 1 DNA lacks a 2 OH hydroxyl This means that DNA can t be readily hydrolyzed resulting in greater stability when compared to RNA 2 DNA contains thymine instead of uracil cytosine to uracil reaction a At very low concentrations in DNA cytosine is deaminated resulting in the formation of uracil When DNA sees uracil it knows that there should actually be a cytosine there This is then fixed so that any uracil on a DNA molecule is converted back to cytosine