NUCLEIC ACID CHEMISTRY

1. THE NUCLEIC
ACIDS
DR SAKINA ROOHI
MBBS. M.D

2. OUT LINE
• INTRODUCTION
• NUCLEOSIDE
• NUCLEOTIDE
• DNA STRUCTURE
• RNA STRUCTURE

3. Nucleic Acid
Nucleic acids were first isolated by
Friedrich Miescher in 1869.
Nucleotides are precursors of
nucleic acid DNA & RNA

4. sugar base
phosphate
sugar base
phosphate
sugar base
phosphate
sugar base
phosphate
sugar base
Nucleoside
Nucleotides
Nucleic acids
1 2
3
2
1

5. PENTOSE
C1
C5
C4
O
C3 C2

7. Nitrogenous Bases
Purines (double-ring
structures)
A and G
Pyrimidines (single-ring
structures)
C, T, and U
hyperphysics.phy-astr.gsu.edu

8. PURINES AND PYRIMIDINES
Purines and pyrimidines are
AROMATIC HETEROCYCLIC COMPOUNDS
contain both carbon and other elements (hetero atoms).

9. Purine & Pyrimidine

10. BIOLOGICALLY IMPORTANT BASES

11. NUCLEOSIDE
• Nucleosides are derivatives of purines and pyrimidines that
have a sugar linked to a ring nitrogen.
The sugar is linked to the heterocyclic base via a
β-N-glycosidic bond,
almost always to N-1 of a pyrimidine or to N-9 of a purine.

12. NUCLEOTIDE STRUCTURE
PHOSPATE SUGAR
Ribose or
Deoxyribose
NUCLEOTIDE
BASE
PURINES PYRIMIDINES
Adenine (A)
Guanine(G)
Cytocine (C)
Thymine (T)
Uracil (U)

13. NUCLEOTIDE

14. PHOSPHODIESTER BOND

16. Tautomerism of the Bases

17. Important Analogs of Purine
Pyrimidine &Nucleotides
• 1.Allopurinol-used in treatment of gout
• 2.Azathioprine-suppress immunological rejection during
transplantation
• 3.Arabinosyladenine-used in treatment of neurological diseases
• 4.Arabinosylcytosine-used in cancer therapy
• 5.Drugs used in AIDS are sugars modified synthetic nucleotide
Analogs

19. DNA-The Double Helix (1953)

20. The DNA Double Helix

21. THE SUGAR-PHOSPHATE
BACKBONE
• The nucleotides are all orientated in the
same direction
• The phosphate group joins the 3rd Carbon
of one sugar to the 5th Carbon of the next
in line.
P
P
P
P
P
P

22. ADDING IN THE BASES
• The bases are attached to the 1st
Carbon
• Their order is important
It determines the genetic
information of the molecule
P
P
P
P
P
P
G
C
C
A
T
T

23. DNA IS MADE OF
TWO STRANDS OF
POLYNUCLEOTIDE
P
P
P
P
P
P
C
G
G
T
A
A
P
P
P
P
P
P
G
C
C
A
T
T
Hydrogen bonds

24. Chargaff’s Rules:
A=T and G=C
purines = pyrimidines

25. The DNA Double Helix

26. A, B and Z Forms of DNA

28. OTHER FORMS OF DNA
STRUCTURE
BENT DNA
TRIPLE STRANDED DNA
FOUR STRANDED DNA
IT IS BELIEVED THAT SUCH STRUCTURES
ARE IMPORTANT FOR MOLECULAR
RECOGNITION OF DNA BY PROTEINS AND
ENZYMES

29. OTHER FORMS OF DNA
Hoogsteen Hydrogen bonds

30. ORGANISATION OF DNA
The Nucleosome -
DNA (146 bp) wrapped around
octamer of core histone proteins (+
linker DNA = ~200 bp)

31. • Much more abundant than DNA
• Single stranded structure
• Contains ribose (DNA 2’-deoxy ribose)
• Contains uracil base
• Does not obey Chargaff ’s rule
• Susceptible to alkaline hydrolysis
• Retains all information of DNA
• Specific RNA for specific functions
• Structure similar to A-form DNA
• 3 major types
• mRNA : 5-10%
• tRNA: 10-20 %
• rRNA: 50-80 %

32. Dr Aminu 10/27/14

33. 33