Structure of dna

Structure of dna

1. THE STRUCTURE OF DNA BY SANJAY SINGH BHOJ M.Sc 1 st SEMESTER,ZOOLOGY

2. DNA STRUCTURE DNA is composed of two polynucleotide chain, twisted around each other in the form of a double helix.

3. Each nucleotide is made up of the three parts: A cylic five carbon sugar(D-ribose or D-2- deoxyribose) A heterocyclic nitrogenous base (Purine or Pyrimidines) Phosphoric acid or phosphate .

4. A. PHOSPHATE The molecular formula of phosphoric acid is H3PO4. It contains 3 monovalent hydroxyl groups and a divalent oxygen atom, all linked to the pentavalent phosphorus atom.

5. PENTOSE SUGAR DNA containing = β -D-2 deoxyribose.

6. An important property of the pentoses is their capacity to form esters with phosphoric acid. In this reaction the OH groups of the pentose, especially those at C3 and C5, are involved forming a 3′, 5′- phosphodiester bond between adjacent pentose residue.

7. NITROGENOUS BASES Two types of nitrogenous bases are found in all nucleic acids. The base is linked to the sugar moiety by the same carbon (C1) used in sugar-sugar bonds. The nitrogenous bases are derivatives of pyrimidine and purine.

8. 1. PYRIMIDINE DERIVATIVES The common pyrimidine derivative found in nucleic acids are:

9. PURINE DERIVATIVES These are all derived from their parent compound purine, which contains a six-membered pyrimidine ring fused to the five-membered imidazole ring .

10. Adenine (C5H5N5), found in both RNA and DNA. Guanine (C5H5ON5), also found in both RNA and DNA, is a colourless . first isolated from guano (bird manure), hence so named.

11. NUCLEOSIDE AND NUCLEOTIDE The nucleosides are compounds in which nitrogenous bases (purines and pyrimidines) are conjugated to the pentose sugars (ribose or deoxyribose) by a β-glycosidic linkage.

12. Nucleotides are the phosphoric acid esters of nucleosides. These occur either in the free form or as subunits in nucleic acids. Formation of nucleotide by removal of water.

13. Watson- Crick ribbon model of B-DNA

14. The Double Helix Has Major and Minor Groove The two grooves arise because the glycosidic bonds of a base pair are not diametrically opposite each other. The angle between the glycosidic bonds is about 120˚for narrow angle and 240˚ for wide angle. Each groove is lined by potential hydrogen bond donor and acceptor atoms. The major groove is rich in chemical information.

15. The letters in red identify hydrogen bond acceptor (A) , hydrogen bond donor (D) , nonpolar hydrogen (H) and methyl group (M).

16. STABILITY OF DNA (A) Hydrogen bonding give structural stability to a molecule with large number of them. The two common watson-Crick base pairs of DNA:

17. (B) Base stacking provide chemical stability to DNA double helix. Schematic diagram showing how the base pairs (colored rectangles) can stack onto each other without a gap by means of a helical twist.

18. The double helix exist in multiple conformation.

19. REFERENCES Lizabeth A. Allison, Fundamental molecular biology

20. THANK YOU