NUCLEOTIDES

 

INTRODUCTION:  In 1868, F. Miescher isolated nucleic acid by then called nuclein from pus cells.  Later, A. Kossel won a Nobel prize in 1910 after he differentiated RNA and DNA in 1882.  In 1906, Kossel described the 4 bases in nucleic acids.  Nucleotides are precursors of the nucleic acids, deoxy-ribonucleic acid (DNA) and ribonucleic acid (RNA).  The nucleic acids are concerned with the storage and transfer of genetic information.  The universal currency of energy, namely ATP, is a nucleotide derivative. Nucleotides are also components of important co-enzymes like NAD+ and FAD, and metabolic regulators such as cAMP and cGMP.  [STRUCTURE OF RNA]

COMPOSITION OF NUCLEOTIDES:  A nucleotide is made up of 3 components:  (1) Nitrogenous base, which can be a purine or a pyrimidine.  (2)  Pentose sugar, either ribose for RNA or deoxyribose for DNA.  (3) Phosphate groups esterified to the sugar. 

GENERATION OF A NUCLEOTIDE:  When a base combines with a pentose sugar, a nucleoside is formed.  When the nucleoside is esterified to a phosphate group, it is called a nucleotide or nucleoside mono-phosphate.  When a second phosphate gets esterified to the existing phosphate group, a nucleoside diphosphate is generated.  The attachment of a 3^rd phosphate group results in the formation of a nucleoside triphosphate.  The nucleic acids (DNA and RNA) are polymers of nucleoside monophosphates.

BASES PRESENT IN THE NUCLEIC ACIDS: Two types of nitrogenous bases; the purines and pyrimidines are present in nucleic acids.

Purine Bases:  The purine bases present in RNA and DNA are the same; adenine and guanine.  Adenine is 6-amino purine and guanine is 2-amino, 6-oxypurine.

Minor Purine Bases:  These bases may be found in small amounts in nucleic acids and hence called minor bases.  These are hypoxanthine (6-oxopurine) and xanthine (2, 6-di-oxopurine).  Uric acid (2,6,8-tri-oxopurine) is formed as the end product of the catabolism of other purine bases. 

Pyrimidine Bases:  The pyrimidine bases present in nucleic acids are cytosine, thymine and uracil.  Cytosine is present in both DNA and RNA. Thymine is present in DNA and uracil in RNA.  A few other modified pyrimidine bases like dihydrouracil and 5-methyl cytosine are also found rarely in some types of RNA.  

RELATED;

1.  DNA, THE GENETIC MATERIAL

2.  RNA, THE GENETIC MATERIAL

3.  PROTEINS

4.  AMINO ACIDS

5.  LIPIDS

REFERENCES