Overview of
Nitrogen Metabolism
The
Nitrogen Cycle Maintains a Pool of Biologically
Available Nitrogen
Nitrogen
Is Fixed by Enzymes of the Nitrogenase Complex
Ammonia Is
Incorporated into Biomolecules through Glutamate
and Glutamine
Glutamine
Synthetase Is a Primary Regulatory Point in
Nitrogen Metabolism
Several
Classes of Reactions Play Special Roles in the
Biosynthesis of Amino Acids and Nucleotides
Biosynthesis of
Amino Acids
a-Ketoglutarate
Gives Rise to Glutamate, Glutamine, Proline, and
Arginine
Serine,
Glycine, and Cysteine Are Derived from
3-Phosphoglycerate
Three
Nonessential and Six Essential Amino Acids Are
Synthesized from Oxaloacetate and Pyruvate
Chorismate
Is a Key Intermediate in the Synthesis of
Tryptophan, Phenylalanine, and Tyrosine
Histidine
Biosynthesis Uses Precursors of Purine
Biosynthesis
Amino
Acid Biosynthesis Is under Allosteric Regulation
Molecules Derived
from Amino Acids
Glycine
Is a Precursor of Porphyrins
Degradation
of Heme Yields Bile Pigments
Amino
Acids Are Required for the Biosynthesis of
Creatine and Glutathione
D-Amino
Acids Are Found Primarily in Bacteria
Aromatic
Amino Acids Are Precursors of Many Plant
Substances
Amino
Acids Are Converted to Biological Amines by
DecarBOXylation
Biosynthesis and
Degradation of Nucleotides
BOX 21-1 Curing
African Sleeping Sickness with a Biochemical Trojan Horse
De Novo
Purine Synthesis Begins with PRPP
Purine
Nucleotide Biosynthesis Is Regulated by Feedback
Control
Pyrimidine
Nucleotides Are Made from Aspartate, PRPP, and
Carbamoyl Phosphate
Pyrimidine
Nucleotide Biosynthesis Is Regulated by Feedback
Inhibition
Nucleoside
Monophosphates Are Converted to Nucleoside
Triphosphates
Ribonucleotides
Are the Precursors of the Deoxyribonucleotides
Thymidylate
Is Derived from dCDP and dUMP
Degradation
of Purines and Pyrimidines Leads to Uric Acid and
Urea, Respectively
Purine
and Pyrimidine Bases Are Recycled by Salvage
Pathways
Overproduction
of Uric Acid Causes Gout
Many
Chemotherapeutic Agents Target Enzymes in the
Nucleotide Biosynthetic Pathways
Summary
Further Reading
Problems
