Overview of nitrogen metabolism

Overview of nitrogen metabolism

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 A nabolic processes are : ( i) Nitrogen fixation ( ii) Amino acid synthesis ( iii) Protein synthesis C atabolic 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 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 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 n itrite

9. OVERVIEW OF NITROGEN METABOLISM, BHUVANA A R, ST.MARY’S COLLEGE - THRISSUR The second step in nit rificat ion 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 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 + H 2 O

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