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  Chemistry of nucleotides, Biology tutorial

Introduction:

Monomeric units of nucleic acids (RNA & DNA) are nucleotides. Such nucleotides are of different kinds and structures. They are also of physiological importance in cells and tissues where they are found. On limited hydrolysis of nucleic acids, nucleotides can be attained. Structure of every protein, every biomolecule and cellular component is the product of information programmed in nucleotide sequences in form of genes.

Definition of nucleotides:

Nucleotides are phosphoric acid esters of nucleosides. They have nitrogenous bases and sugars that are esterified to the phosphoric acid residue. Esterification could be either at positions (2, 3 or 5) in ribose and (3 or 5) in deoxyribose where ester bonds could be formed. Additionally, nucleotides could be in form of mono, di and triphosphates.

Components of nucleotides:

Nucleotides have nitrogenous bases, sugars and phosphoric acids in ester linkage. Similar to nucleosides, nitrogenous base, present in nucleotides are purines: Adenine and Guanine; pyrimidines: Cytosine, Thymine and Uracil. Uracil can only be found in ribonucleotides whereas thymine base can only be found in deoxyribonucleotides. Sugar in nucleotides is pentose sugar that could be ribose and deoxyribose.

Nomenclature of nucleotides:

Nucleotides are strong acids and thus are known as guanylic acid, adenylic acid, thymidylic acid, cytidylic and undylic acids. All the nucleotides are monophosphate derivatives of their corresponding nucleotides and ribonucleotides. In all examples given, phosphate groups are on position 5 of the sugar. Though, product of enzymatic or alkaline hydrolysis of RNA yields 2', 3' or 3',5' monophosphates.

When phosphate is on position 2, nucleotide is named ribo nucleoside 2' monophosphate e.g. adenosine 2' monophosphate. When phosphate is on position 3, nucleoside is known as ribo nucleoside 3' the monophosphate. Ribonucleoside could be cyclic monophosphate where single phosphate is attached on carbon atoms or position 2'and 3' at same time like Adenosine 2'3' cyclic monophosphate (cAMP). When more than one phosphate is bonded to the nucleoside e.g. 2 or 3, terms di and triphosphates are used respectively like Adenosine diphosphate (ADP) and Adenosine triphosphate (ATP).

Derivatives of nucleotides:

Nucleotide derivatives are compound which have their structures derived from some nucleotide structures. They have nucleotide components and thus nucleotide share close structural features. Different kinds of nucleotide derivatives do exists; examples comprise: Nicotinamide Adenine dinucleotide (NAD), Nicotinamide Adenine dinucleotide phosphate (NADP), flavine adenine dinucleotide (FAD) among others.

Significance of nucleotides/nucleotide Derivatives:

  • Nucleotides play important roles in cellular metabolism like ATP which acts as energy currency of living cells. Energy utilized by cells is derived from the nucleotide molecule.
  • Nucleotides also act as coenzymes for significant enzyme catalyzed reactions NAD and FAD are two coenzymes which are involved in oxidation-reduction reaction in living cells. Reactions of the Krebs's cycle involve the coenzymes.
  • Nucleotide have also been found to play role in metabolic regulation. The derivative of AMP, cyclic AMP (cAMP) is directly engages in process.
  • Nucleotides also act as source of electrons (H+) in reductive biosynthetic pathways like synthesis of cholesterol, NADPH2 is very applicable in process.

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