Structure of dna

1. BY SANJAY SINGH BHOJ
M.Sc 1st 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