Lecture Twelve : Nucleic Acids and DNA Convener : Dr. Fawaz Aldabbagh First Year Organic Chemistry Biological Chemistry

Two Nucleic Acids (Polymers) – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) Mild degradation yields monomeric units Nucleotides Complete degradation yields 1.A Heterocyclic Base 2.A five Membered Monosaccharide 3.A Phosphate ion Pyrine or Pyrimidine D-Ribose or 2-deoxy-D-ribose

The Phosphate ester can be at C-5’ or C-3’ Hydolysis of Phosphate Nucleoside

Tautomerism (see Keto-Enol Tautomerism notes) Simultaneous shift of a proton and a pair of electrons

Nucleosides that can be obtained from DNA

Nucleosides that can be obtained from RNA

Nucleotides are held together by phosphate ester linkages. Phosphate esters link 3’- OH of one ribose (or deoxyribose) with the 5’-OH of another. This makes the nucleic acid a long unbranched chain with a backbone of sugar and phosphate units with heterocyclic bases protruding from the chain at regular intervals. Base Sequence is the Genetic Code Primary Structure

Secondary Structure Two Complementary Chains Result E. Chargaff

Double Helix is the Secondary Structure of DNA Two nucleic acid chains are held together by weak H-bonds between bases of opposite strands Wound into a helix with a common axis The base pairs are on the inside of the helix and the sugar-phosphate backbone is on the outside 34A repeating unit contains 10 successive nucleotide pairs Phosphate-Sugar backbone is regular, base pairs can assume many different permutations

Watson-Crick Model of DNA (1953)

Replication of DNA Just prior to cell division the double strands of DNA begin to unwind Complementary Strands are formed along each chain Each chain acts in effect as a template for the formation of its complement When unwinding and duplication are complete, there are two identical DNA molecules where only one had existed before These two molecules can then be passed on, one to each daughter cell

A Gene is the segment in DNA, which contains the necessary information to direct the synthesis of one protein

RNA is a single-stranded molecule, thus RNA unlike DNA does not contain equal amounts of specific bases RNA molecules are much smaller than DNA RNA can fold back on itself to give double helical regions, if complementary regions along an RNA strand exist

Synthetic Nucleic Acid Bases in Medicine 1988, Nobel Prize for Medicine Professor Sir James Black Gertrude Elion and George Hitchings Inhibitors of Nucleic Acid Synthesis