1. 1 Biochemistry of nucleotides & Nucleic Acids By Dr. Howeida Abdullah Mustafa. Lecture 2 Components & Formation of nucleotides & Nucleic acids.

2. Components of nucleotides Nucleotides which are precursors of nucleic acids are composed of: 1- Nitrogenous bases 2- 5-carbon sugars 3- Phosphoric acid. 2

3. Components of nucleotides 1- Nitrogenous bases They are derived either from A- Purine B- Pyrimidine 3

4. Purines Purines are heterocyclic bases that have 2 rings. A purine is made up of 9 atoms making up fused rings of 5 Carbons & 4 Nitrogens numbered 1-9. A Pyrimidine: Has one ring. Is made up of 6 atoms composed of 4 Carbons & 2 Nitrogens numbered 1-6. 4

5. PyrimidinePurine CytosineAdenine ThymineGuanine Uracil 5

6. The Purines The Pyrimidines 6

7. (2)- Sugars The sugars involved in the formation of nucleotides are 5- carbons sugars. They are two sugars 1-Ribose: Which contains oxygen and contribute in the formation of Ribonucleic acid (RNA). 2- Deoxyribose: Which contains no oxygen and contributes in the formation of Deoxyribonucleic acid DNA. 7

8. 8 Sugars

9. (3)- Phosphate Phosphate is the third component of nucleotide. Therefore: Nucleotide = N-base + Sugar+phosphate. N-base +Sugar= a nucleoside, Therefore a nucleotide = a nucleoside + phosphate. 9

10. Nomenclature of nucleosides N- baseSugarNucleoside Adenine(deoxy) ribose (deoxy) ribo adenosine Cytosine(deoxy) ribose(deoxy) ribo cytidine Guanine(deoxy) ribose(deoxy )ribo guanidine ThymineDeoxy riboseDeoxyribo thymidine UracilriboseRibo uridine 10

11. 11 Nucleoside Nucleotide = nucleoside + phosphate Sugar Base PO 4 Nucleotide

12. Linkage between the N-base and Sugar The linkage between the N-base and the sugar is known as N-glycosyl linkage. 1. In a pyrimidine base the N-glycosyl bond is linking nitrogen in carbon -1 of the base to C-1 of sugar. 2. In a purine base, it links Nitrogen in C-9 of the base with C-1 of the sugar. 12

13. Linkage of o phosphate to a nucleoside N-base + Sugar ( N-glycosyl bond ) nucleoside Linkage of a phosphate to a nucleoside: Phosphate is added to nucleoside to form a nucleotide. The Posphate is added at C – 5 of the sugar. 13

14. Internucleotide linkage The internucleotide linkage between the sugars ( in a nucleotide) is a strong phospdiester bond known as: 3'-5' phosphodiester bond. In DNA and RNA, the phosphodiester bond is the linkage between the 3' carbon atom of one sugar molecule and the 5' carbon of another.DNARNA carbonatom In DNA the sugar is deoxyribose and in RNA, it is ribose. 14

15. 15 Nucleotides in DNA and RNA DNA dAMPDeoxyadenosine monophosphate dGMPDeoxyguanosine monophosphate dCMPDeoxycytidine monophosphate dTMPDeoxythymidine monophosphate RNA AMPadenosine monophosphate GMPguanosine monophosphate CMPcytidine monophosphate UMPuridine monophosphate

16. Cyclic nucleotides 1- cAMP Cyclic nucleotides play a major role in actions of hormones. They act as 2 nd messengers. Cyclic AMP is synthesized from ATP by the action of the enzyme adenylyl cyclase.ATP Once a hormone binds its receptors, the complex formed activates a G protein (guanine nucleotide) which, in turn, stimulates adenylyl cyclase, to remove phosphate from ATP forming cAMP.G protein c AMP turns on the appropriate response in the cell. 16

17. 2- c GMP Cyclic GMP is synthesized from the nucleotide GTP using the enzyme guanylyl cyclase.GTP Cyclic GMP serves as the second messenger for certain hormones. Some of the effects of c GMP are mediated through Protein Kinase G that phosphorylates target proteins in the cell. 17