Nucleic acids and Nucleotides

Nucleic acids and Nucleotides


      Introduction to nucleotides

      Types of nucleic acid and components


      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


       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


                It is composed of

                                                                Nitrogen base

                                                                Pentose sugar


       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 2nd 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 pH the lactam tautomeric forms are present


       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 5l or 3l 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


       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



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