Biochemistry of nucleotides & Nucleic Acids

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.

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

4. Purines • Purinesare heterocyclic bases that have 2 rings. • A purineis 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 Nitrogensnumbered 1-6.

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.

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.

10. Nomenclature of nucleosides

11. Nucleotide Nucleoside Nucleotide = nucleoside + phosphate Base PO4 Sugar

12. Linkage between the N-base and Sugar • The linkage between the N-base and the sugar is known as N-glycosyllinkage. • 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.

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.

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' carbonatomof one sugar molecule and the 5' carbon of another. In DNA the sugar is deoxyribose and in RNA, it is ribose.

15. Nucleotides in DNA and RNA DNA dAMP Deoxyadenosine monophosphate dGMP Deoxyguanosine monophosphate dCMP Deoxycytidine monophosphate dTMP Deoxythymidine monophosphate RNA AMP adenosine monophosphate GMP guanosine monophosphate CMP cytidine monophosphate UMP uridine monophosphate

16. Cyclic nucleotides1- cAMP • Cyclic nucleotides play a major role in actions of hormones. They act as 2nd messengers. • Cyclic AMP is synthesized from ATP by the action of the enzyme adenylyl cyclase. • 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. • c AMP turns on the appropriate response in the cell.

17. 2- c GMP • Cyclic GMP is synthesized from the nucleotide GTPusing the enzyme guanylyl cyclase. • 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.