are phosphorylated forms of nucleosides. Phosphorylation (addition
A nucleotide with one phosphate group is called as monophosphate
of the respective nucleoside. For example, the monophosphate of adenosine is
called as Adenosine Mono Phosphate. If two phosphate groups are attached to the
sugar moiety at the 5΄OH group, it is called as diphosphate. eg. Cytidine
Diphosphate.A nucleotide containing three phosphate
groups is called as triphosphate eg. Adenosine Triphosphate (Fig. 7.5). The
corresponding nucleosides and nucleotides are listed in Table 1 (Bases, their
Nucleotides are the energy currency of the cells (ATP).
They actively take part in metabolism as hydrogen donors, phosphate
group donors and methyl group donors.
They form the structural components of some co-enzymes (NAD and FAD).
Nucleotides like cAMP (cyclic AMP) and cGMP (cyclic GMP)
act as second messengers involved in hormonal signaling pathways.
Table 7.1 Bases, their nucleosides and nucleotides
Oligonucleotides are polymers which yield two to ten residues of mononucleotides on hydrolysis. Two nucleotides join together to form dinucleotides.Example for biologically important dinucleotides are NAD and FAD, which act as co-enzymes.
are polymers that yield more than ten nucleotides on hydrolysis.
have directions. If the first nucleotide of the sequence has 5΄ triphosphate
free and 3΄OH group bonded to the next nucleotide, then the direction of the
polynucleotide is 5΄to 3΄. If the first nucleotide
in the sequence has 3΄OH group free, then it is said to be from 3΄to