Chapter 20 Nitrogen Metabolism

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Chapter 20 Nitrogen Metabolism
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1. Nitrogen in the bioscphere
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Nitrogen in the biosphere
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• Nitrogen in the bioscphere
• Nitrogen fixation

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Nitrogen Fixation

• Bacteria are responsible for the reduction of N2
  to NH3
• typically they are symbiotic organisms that form
  nodules on the roots of leguminous plants

• reduction is catalyzed by the nitrogenase enzyme
  complex

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• N2 to ammonium ion is a six-electron
• reduction

• reduction is coupled with the
• hydrolysis of 12ATP

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• Nitrogen in the bioscphere
• Nitrogen fixation
• Amino acid metabolism
• a. Incorporation of NH4
• Reductive amination
• Amidation
• Transamination

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Amino acid anabolism
How is ammonia incorporated into amino acids?

• Glutamate is formed by reductive amination of
  ?-ketoglutarate

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• amidation of glutamate gives glutamine

amide
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How is ammonia incorporated into other amino
acids?
Transamination Vitamin b6
pyridoxal phosphate
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Pyridoxal Phosphate

• The biologically active form of vitamin B6 is
  pyridoxal phosphate (PyrP)
• PyrP participates in the catalysis of a wide
  variety of reactions of amino acids, including
  transaminations and decarboxylations

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• Nitrogen in the bioscphere
• Nitrogen fixation
• Amino acid synthesis
• a. Incorporation of NH4
• Reductive amination
• Amidation
• Transamination
• b. Forming carbon skeletons importance of the
  citric acid cycle.

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Amino acids can be divided into families
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Amino acids and the citric acid cycle.
Catabolism
Anabolism
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• Nitrogen in the bioscphere
• Nitrogen fixation
• Amino acid synthesis
• a. Incorporation of NH4
• Reductive amination
• Amidation
• Transamination
• b. Forming carbon skeletons importance of the
  citric acid cycle.
• c. Transferring 1C units

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Transferring 1C units Biotin Folic
acid S-adenoxyl methionine
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• Nitrogen in the bioscphere
• Nitrogen fixation
• Amino acid synthesis
• a. Incorporation of NH4
• Reductive amination
• Amidation
• Transamination
• b. Forming carbon skeletons importance of the
  citric acid cycle.
• c. Transferring 1C units.
• d. Essential amino acids

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Essential Amino Acids
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• Catabolism of amino acids
• A. Carbon skeletons

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Catabolism of amino acids

• First step is removal of the ?-amino group by
  transamination
• it is transferred to ?-ketoglutarate to give
  glutamate and an ?-ketoacid
• The breakdown of carbon skeletons follows two
  pathways, depending on the type of endproduct
• glucogenic amino acid one whose carbon skeleton
  is degraded to pyruvate or oxaloacetate, both of
  which may then be converted to glucose
• ketogenic amino acid one whose carbon skeleton
  is degraded to acetyl-CoA or acetoacetyl-CoA,
  both of which may then be converted to ketone
  bodies

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• Catabolism of amino acids
• A. Carbon skeletons
• B. Excreting excess nitrogen

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• The ?-amino group which has been transferred to
  ?-ketoglutarate may
• be used for biosynthesis
• excreted as one of the following

Fish Mammals
Birds
Kangaroo
Rat
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Ammonia is released from glutamate by Glutamate
dehydrogenase.
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The Urea Cycle
Mitochondria
ATP
CA cycle
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