Nucleotide structure function dr m muzaffar mir

1. 1
Nucleosides and Nucleotides
Dr M Muzaffar Mir
Professor of Medical Biochemistry
University of Bisha
Kingdom of Saudi Arabia

2. Learning objectives
• Outline the structure of nitrogen bases and the
pentose sugar.
• Differentiate between nucleosides and nucleotides.
• Explain the importance of nucleotides as energy
molecules.
• Identify the role of nucleotides as monomer units of
nucleic acids.
• Harpers Illustrated Biochemistry, 29th Edition; Chapter 32, pages 323-326
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3. Pyrimidines and Purines
• Pyrimidine and purine are the names of the parent
compounds of two types of nitrogen-containing
heterocyclic aromatic compounds that are present in
DNA and RNA
• In addition to carbon their rings contain nitrogen
atoms (thus heterocyclic)
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4. Important Purines
Adenine and guanine are the principal
purines of both DNA and RNA.
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5. Important Pyrimidines
Pyrimidines that occur in DNA are cytosine and
thymine. Cytosine and uracil are the
Pyrimidines in RNA.

6. Tautomer forms of Bases
• The oxo and amino group of purines and pyrimidines
show keto-enol and amine-imino tautomerism.
• But physiological conditions favor amino and keto forms
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7. Sugars in nucleotides
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8. Nucleosides
• Nucleosides are Formed by Joining a Nitrogenous
Base to a Ribose Sugar
• A ribose and nitrogenous base are covalently joined by
a glycosidic bond to form a nucleoside molecule
• Glycosidic bonds in nucleosides are always b-
type glycosidic bonds
• Nucleosides are named by adding the suffix "-idine" to
the pyrimidine or "-osine" to the purine name.
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9. • Pyrimidine nucelosides include Cytidine,
Thymidine, and Uridine
• Purine nucleosides include Adenosine and
Guanosine
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Nucleosides

10. Deoxyribonucleotides for DNA
• The above nucleosides are all
ribonucleosides as is found in RNA.
• Deoxyribonucleosides are found in
DNA, and include deoxy-thymidine
instead of Uridine.
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11. syn and anti Conformation
• Rotation around the glycosidic bond is restricted
due to the presence of the hydrogen of the C2'
carbon of the ribose
• There are two general orientations of the
base: syn and anti
• Both forms occur in nature but anti
conformers predominate
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12. Nucleotides are Nucleoside
Phosphates
• A nucleotide is formed when phosphoric acid is
esterified to a sugar hydroxyl of a nucleoside
• The vast majority of biological nucleotides involve the
sugar hydroxyl at the 5' position.
• Some nucleotides also involve the 3' position. No
OH group is available at the 2' position in DNA.
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13. Nucleoside diphosphates and
triphosphates
• Additional phosphoric acid groups can be linked to the existing
phosphate in nucleotide monophosphates to produce di- and tri-
phosphates.
• The linkage between phosphate groups is a high energy
phosphoric anhydride linkage
• The phosphate on the 5' carbon is labeled "a", and successive
phosphates are labeled "beta" and "gamma"
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14. Nucleoside di and triphosphates
• NDP, and NTP (where N is the base) represent
the different nucleoside diphosphate and
triphosphate structures.
• dNDP and dNTP represent the corresponding
deoxynucleoside di- and tri-phosphates.
•
• Nucleoside di- and tri- phosphates all occur as
free molecules within the cell.
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15. Oligonucleotides
• Oligonucleotides are polymers of
nucleic acids via 3'à 5' phosphodiester
bondse. e.g. DNA and RNA
• Oligonucleotides are synthesized
by polymerase enzymes from NTP's or
dNTP's
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16. Cyclic nucleotides
• Nucleoside monophosphates can have two ester
bonds to the phosphoric acid, and these can
be within the same molecule via an ester bond to both
the 5' and 3' hydroxyl groups of the ribose sugar.
• Thus cyclic nucleotides are formed
• cAMP, and cGMP are important regulators (as
second messengers) of cell metabolism and are found
in virtually all cells
• Hormones (the "first messengers") stimulate the
formation of cAMP and cGMP.
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17. 17
cAMP cGMP

18. Nucleotides as high energy compounds
• ATP is a unique and important high energy
compound with High Phosphoryl
Potential.
• ATP is hydrolyzed to yield energy
ATP + H2O → ADP +Pi + 7.3 KCal
• ATP serves as the Universal Energy currency of Cell as
it is being constantly utilized and regenerated in ATP-
ADP cycle.
• ATP also acts a phosphate donor to low energy
phosphate compounds. 18

19. Functions of Nucleotides
• Nucleotides are the basic units of nucleic acids (DNA and RNA)
• Cyclic Nucleotides Act as Regulatory Chemicals. cAMP and c GMP
• Nucleotides of B-Complex Vitamins Function as Coenzymes. For
example, NAD+, NADP+, FMN, FAD are coenzymes useful in oxidation-
reduction reactions.
• Nucleotides function as energy carriers, e.g. ATP, GTP, UTP and TTP.
Out of these ATP is the universal energy carrier of the cell.
• Nucleotides are involved in the synthesis of polysaccharides (e.g.
UDP-glucose, ADP-glucose) and phospholipids (e.g. CDP and CTP).
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