The document provides an overview of nitrogen metabolism. It discusses (1) the importance of nitrogen in proteins and nucleic acids, (2) the key anabolic processes of nitrogen fixation, amino acid synthesis and protein synthesis, and (3) the main catabolic processes of proteolysis, nitrification and denitrification. Nitrogen is obtained from the atmosphere through nitrogen fixation by bacteria and is used to synthesize amino acids and proteins essential for plant structure and function.

1. OVERVIEW OF NITROGEN METABOLISM
BHUVANA A R AND Dr. KAYEEN VADAKKAN
DEPARTMENT OF BIOTECHNOLOGY
ST. MARY’S COLLEGE, THRISSUR

2. OVERVIEW OF NITROGEN METABOLISM, BHUVANA A R, ST.MARY’S COLLEGE - THRISSUR
INTRODUCTION
 The entire spectrum of living chemical reactions ,
occurring in living systems - METABOLISM
 Metabolism is broadly classified into two :
 CATABOLISM – degradative processes concerned
with the breakdown of complex molecules to
simpler ones with release of energy.
 ANABOLISM – biosynthetic reactions involving in the
formation of complex molecules from simple
precursors.

3. OVERVIEW OF NITROGEN METABOLISM, BHUVANA A R, ST.MARY’S COLLEGE - THRISSUR
NITROGEN METABOLISM
 Polymeric nitrogen containing compounds
proteins and nucleic acids that define the major
attributes of organism such as function and
structure.
 Operation and mechanism of metabolic pathways
is provided by proteins.
 Genetic information is stored in nucleic acid
polymers.
 Each of the monomer of these macromolecules
has an individual metabolic pathway.

4. OVERVIEW OF NITROGEN METABOLISM, BHUVANA A R, ST.MARY’S COLLEGE - THRISSUR
PROCESSES OF NITROGEN METABOLISM
 Nitrogen - most prevalent essential macro- elements
which regulates plant growth, especially in agricultural
systems.
 Main source of nitrogen for the construction of
nitrogenous organic compounds is the atmosphere.
 Plants require higher amounts of nitrogen as it is
important in their structure and metabolism.
 But unfortunately ,most plants cannot utilize it in its
elementary form. So they have to depend on the soil
and they acquire nitrogen in inorganic form either as
ammonium compounds or as nitrate.

5. OVERVIEW OF NITROGEN METABOLISM, BHUVANA A R, ST.MARY’S COLLEGE - THRISSUR
 Nitrogen metabolism includes both anabolic and catabolic processes
 Anabolic processes are:
(i) Nitrogen fixation
(ii) Amino acid synthesis
(iii) Protein synthesis
 Catabolic processes are:
(i) proteolysis and amino acid destruction
(ii) de-nitrification
(iii) nitrification

6. OVERVIEW OF NITROGEN METABOLISM, BHUVANA A R, ST.MARY’S COLLEGE - THRISSUR
1. NITROGEN FIXATION
 Process by which inorganic molecular nitrogen (N2)
from the atmosphere is incorporated first into ammonia
and then into organic compounds that are useful to
organism.
N2 + 8H+ + 8e- + 16 ATP = 2NH3 + H2 + 16ADP + 16 Pi
STEPS:
 Atmospheric nitrogen is reduced by the
addition of hydrogen atoms.
 As a result the bonds between the two nitrogen
atoms (N2 N N) are broken down resulting
in the formation of ammonia.
 Ammonia thus formed is used for the synthesis
of amino acids.

7. OVERVIEW OF NITROGEN METABOLISM, BHUVANA A R, ST.MARY’S COLLEGE - THRISSUR
 Biological nitrogen fixation is carried out by a highly conserved
complex of proteins –nitrogenase Complex
 Electrons are transferred from pyruvate to dinitrogenase via
ferredoxin (or flavodoxin) and dinitrogenase reductase.
 Dinitrogenase reductase reduces dinitrogenase one electron at a
time, with at least six electrons required to fix one molecule of N2.
 An additional two electrons are used to reduce 2 H to H2 in a process
that obligatorily accompanies nitrogen fixation in anaerobes, making
a total of eight electrons required per N2 molecule.
 Another important characteristic of the nitrogenase complex is an
extreme liability in the presence of oxygen.

8. OVERVIEW OF NITROGEN METABOLISM, BHUVANA A R, ST.MARY’S COLLEGE - THRISSUR
2. NITRIFICATION
 Nitrification is the biological oxidation of ammonia or ammonium to nitrite
followed by the oxidation of the nitrite to nitrate.
Reaction 1 :converts ammonia to the intermediate,
hydroxylamine, and is catalyzed by the enzyme ammonia
monooxygenase.
Reaction 2 :converts hydroxylamine to nitrite and is catalyzed
by the enyzmer hydroxylamine oxidoreductase.
 The first step is the oxidation of ammonia to nitrite

9. OVERVIEW OF NITROGEN METABOLISM, BHUVANA A R, ST.MARY’S COLLEGE - THRISSUR
 The second step in nitrification is the oxidation of nitrite (NO2-) to nitrate
(NO3-)
3. DENITRIFICATION
 Denitrification is the process that converts nitrate to nitrogen gas.
Reaction 1 : represents the steps of reducing nitrate to dinitrogen
gas.
Reaction 2 represents the complete redox reaction of
denitrification.

10. OVERVIEW OF NITROGEN METABOLISM, BHUVANA A R, ST.MARY’S COLLEGE - THRISSUR
ii) AMINOACID SYNTHESIS
 Ammonia thus formed as a result of nitrogen fixation is not given out .It is
highly toxic and used for the synthesis of amino acids.
 Amino acids are the building blocks for the synthesis of proteins.
 The amino acids are transported through phloem to other parts of the plant
for the synthesis of proteins.
 Majority of amino acids are synthesized in plants by two main processes :
1. Reductive animation :- In this process, ammonia reacts with α - ketoglutaric
acid to form glutamic acid in the presence of enzyme glutamate dehydrogenase.
A reduced coenzyme NADPH in leaves , NADH in roots is required.
α-Ketoglutarate + NH4 + NADPH ͢ L -glutamate + NADP + H2O

11. OVERVIEW OF NITROGEN METABOLISM, BHUVANA A R, ST.MARY’S COLLEGE - THRISSUR
2. Transamination
 Reversible reaction in which an alpha-amino group (-NH2) is enzymatically
transferred from an amino acid1 to an alpha-keto acid2 resulting in formation
of a new amino acid2 and another alpha-keto acid1 (derived from original
amino acid1)
 This pathway is responsible for the deamination of most amino acids.
 One of the major degradation pathways which convert essential amino acids to
nonessential amino acids.

12. OVERVIEW OF NITROGEN METABOLISM, BHUVANA A R, ST.MARY’S COLLEGE - THRISSUR
Eg:
iii) PROTEIN SYNTHESIS
 Proteins are made up of long chains of amino acids.
 form of one or more chain called polypeptide chains.
 Amino acids bond to each other by peptide or amide bonds.

13. OVERVIEW OF NITROGEN METABOLISM, BHUVANA A R, ST.MARY’S COLLEGE - THRISSUR
 The carboxyl group (-COOH) of one amino acid reacts with the amino
group (-NH2)of the next amino acid ,releasing a molecule of water and
as a result peptide bond (-CONH_) is formed.
 This maybe illustrated with the two simplest amino acids, glycine and
alanine:-

14. OVERVIEW OF NITROGEN METABOLISM, BHUVANA A R, ST.MARY’S COLLEGE - THRISSUR