1. Nucleotides, structure and function
By Dr Rehab Omer

2. Nucleotides Structure
Each nucleotide is composed of:
Five-carbon sugar.
Phosphate group.
Nitrogenous base.
Nucleotide subunits of RNA contain a pentose sugar called ribose. Nucleotide subunits of DNA contain the sugar deoxyribose.

3. Structure of purine and pyrimidine nucleotides
nucleotide = phosphate + a nucleoside
nucleoside = Nitrogenous base +pentose sugar
Nitrogenous bases: aromatic heterocycles
purines: pyrimidine + imidazol ring
pyrimidines: pyrimidine ring

4. Structure of bases
Purines and pyrimidines are nitrogen-containing heterocycles compounds whose rings contain both carbon and other elements (hetero atoms).

5. Nitrogenous Bases Structure

6. The nucleosides
Consist of a purine or pyrimidine base linked to a carbohydrate pentose sugar .
This pentoses can be D-ribose as (in RNA) or can be 2-Deoxy –D ribose (in DNA ) .

7. Nucleotides Structure
The five carbon atoms in each pentose are assigned numbers 1/ through 5/. Primes are used in the numbering of the ring positions in the sugar to differentiate them from the ring positions of the bases

8. The nucleosides
nucleosides are formed by coupling of carbon 1of D-ribose or deoxyribose and nitrogen 9 of all purine bases through a 1,9 β-N-glycosidic bond .
or by coupling of carbon 1of D-ribose or deoxyribose and nitrogen 1 of pyrimidine bases (thymine , cytosine ) through a 1,1-β-N-glycosidic bond.

9. ribonucleosides deoxyribonucleoside

10. Nucleotides Structure
Phosphate functional group (PO4):
Gives the DNA and RNA the property of an acid at physiological PH, hence the name nucleic acid.

11. ribonucleotide deoxyribonucleotide

12. Structure of nucleotides
pyrimidine OR
purine
Ribose or
2-deoxyribose
N-b-glycosyl
bond

13. Nucleoside +phosphate (mono, di & tri) Type of bond in nucleotide:
Nucleotides
Nucleoside +phosphate (mono, di & tri)
Type of bond in nucleotide:
* N-glycosidic bond
* ester bond
* anhydride bond

14. Nucleotides Structure

15. The ATP

17. The nucleotides functions
1- Building block of nucleic acids.
2-Energy transduction.
3-Signaling, 2nd messengers.
4- Coenzymes components
5- Regulatory “allosteric” effector.
6- Activated precursors in biosynthesis.

22. The nucleotides and energy
The di- and tri-phosphates of nucleotides are linked by acid anhydride bonds, which have a high ∆G0' for hydrolysis .

24. The adenosine derivatives
The adenosine derivative 3'-5'-cyclic adenosine monophosphate, cAMP is a 2nd messenger in hormonal signal transduction cAMP is also involved in the regulation of ion channels by direct interaction with the channel proteins.

25. Cyclic adenosine monophosphate (cAMP)
3) physiological mediators
cAMP, cGMP („second messengers“)
Cyclic adenosine monophosphate (cAMP)

26. 2nd messenger

27. 4) components of coenzymes
NAD+, NADP+, FAD, CoA

29. Guanosine derivatives
Cyclic GMP (cGMP) is also involved as a second messenger molecule, in many cases, its' role is to antagonize the effects of cAMP.
The most important cGMP coupled signal transduction cascade is the photoreception

30. 5) activated intermediates
UDP-Glc
CDP-choline, ethanolamine, diacylglycerol
6) allosteric effectors
regulation of key enzymes of metabolic pathways

31. Synthetic nucleotides
Synthetic nucleotide analogues are used for therapeutic purposes.
They inhibit specific enzymatic activities.
Interfere with DNA synthesis, preferentially kill rapidly dividing cells, (anti-tumor agents).
Immune suppressors

32. Anti-tumor drugs Disrupt the normal replication process.
The commonly used in anti-tumor chemotherapy include:
6-mercaptopurine,
5-fluorouracil,
5-iodo-2'-deoxyuridine
6-thioguanine.

34. Anti-viral drugs
Nucleotide analogs have also been used to target viruses.
Azidothymidine (AZT) and dideoxyinosine (ddI) are used to interfere with the replication of HIV

35. Enzyme and immune inhibitors
Purine analogs are used to treat gout. allopurinol, resembles hypoxanthine, thus inhibits xanthine oxidase
Also nucleotide analogues are used after organ transplantation to suppress the immune system and reduce rejection.