Nucleic acids and Nucleotides

Nucleic acids and Nucleotides

Contents

–      Introduction to nucleotides

–      Types of nucleic acid and components

Objective

–      At the end of this lecture, student will be able to

–      Explain the types of nucleic acid and their components

–      Discuss the biological functions of nucleotides

–      Describe the nomenclature of nucleotides

–      Distinguish between nucleotide and nucleoside

Introduction

•       Two types of nucleic acid – DNA & RNA

•       It serves as transmitter of genetic information

•       DNA is a chemical basis of heredity and regarded as the reserve bank of genetic information

•       It is responsible for the maintaining the identity of different species of organism over millions of years

•       Every aspects of cell function is under the control of DNA

•       DNA is organized into genes, fundamental unit of genetic information

•       Gene control the protein synthesis

Biological functions of nucleotides

•        Building blocks of nucleic acids (DNA and RNA)

•        Important role in carbohydrate, fat and protein metabolism

•        Purine nucleotides act as high energy source ATP, cyclic AMP  in a wide variety of tissues and organisms

•        Also act as components of coenzymes (NAD, NADP, FAD)

•        Pyrimidine nucleotides act as high energy intermediates such as UDP-glucose and UDP-galactose in carbohydrate metabolism and also in lipid synthesis

Components of Nucleic acid

•       Nucleic acid are the polymers of nucleotides, held by phosphate bridge

•       Nucleotides:

                It is composed of

                                                                Nitrogen base

                                                                Pentose sugar

                                                                Phosphate

•       Nucleoside:        Nitrogen base + pentose sugar

•       Thus nucleotides  are nucleosides + phosphate 

•       The atom in purine ring are numbered as 1 to 9 and for pyrimidine as 1 to 6 where as pentose carbon 1 to 5

•       Nucleic acid are the polymers of nucleotides, held by phosphate bridge

Structure of Nucleotides

•       The nitrogen bases found in nucleotides are aromatic heterocyclic compounds

•       Nitrogen bases are of 2 types:

                                1. Purines:   a. Adenine

                                                         b. Guanine

                                                         These are numbered in anti-clock wise direction

                                2. Pyrimidines:   a. Cytosine

                                                                   b. Thymine

                                                                   c.  Uracil

                                                                These are numbered in clock wise direction

•       DNA & RNA contain the same purines and differ in 2^nd pyrimidine

•       Cytosine is found in both DNA & RNA , but differ in second pyrimidine., i.e. DNA → Thymine and RNA → Uracil

Nitrogen bases structures

Sugars of nucleic acid

•       The five carbon monosaccharides are found in nucleic acid

•       RNA contains D-Ribose while DNA contains D-deoxyribose

•       Ribose and deoxyribose differ in structure at C₂

Nucleic acids – Polynucleotides

•       Two types of nucleic acid – DNA & RNA- made of nucleotides

Tautomeric forms of purines and pyrimidines

•       The existence of a molecule in a keto and enol for is known as tautomerism

•       Purine & pyrimidines with oxo (-c-) functional group exhibits tautomerism

•       The lactam and lactim forms of cytosine are represented as:

•       At physiological p^H the lactam tautomeric forms are present

Nucleotides

•       Pentose are bonded to nitrogen bases by β-N-glycosidic bonds

•       N⁹ of purine ring binds with C¹ of pentose sugar to form a covalent bond in purine nucleotide

•       In case of pyrimidines, glycosidic linkage is between N¹ of pyrimidine and C¹ of pentose

•       The hydroxyl groups of adenosine are esterified with phosphate to produce 5^l or 3^l monophosphate. 5’ hydroxyl is most commonly esterified 

•       Thus AMP represents adenosine 5’ -monophosphate

•       However, for Adenosine-3-monophosphate the abbreviation 3-AMP is used

•       Pentose are bonded to nitrogen bases by β-N-glycosidic bonds

 

•       Nucleotides of DNA

•       Nucleotides of RNA

•       Nucleotide diphosphates and triphosphates

•       Cyclic nucleotides

Summary

•       2 types of nucleic acid DNA and RNA

•        Nucleotides: nucleoside + phosphate

•        Nucleosides: Nitrogen base + pentose sugar

•        DNA & RNA contains both purines and Pyrimidines

•        Purines are Adenine and Guanine

•        Pyrimidines are cytosine, thymine and uracil