Lecture Twelve : Nucleic Acids and DNA

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

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

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

4. Heterocyclic Bases

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

6. Nucleosides that can be obtained from DNA

7. Nucleosides that can be obtained from RNA

8. Base Sequence is the Genetic Code Primary Structure 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.

9. Secondary Structure E. Chargaff Two Complementary Chains Result

11. 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

12. Watson-Crick Model of DNA (1953)

13. 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

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

15. 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

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