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Lesson 17

Nitrogen Metabolism 4

TermDefinition
Why is ammonia toxic to humans? -NH3 can cross membranes and affect H+ gradient -depletes a-ketoglutarate, affecting citric acid cycle
Glutamine synthetase makes glutamine from glutamate, main way to trap NH3, used in many further reactions to add nitrogen
How is ammonia often moved throughout the body? In the form of glutamine, urea, alanine, and glutamate
Role of ATP in glutamine synthetase adds phosphate to the O- of glutamate, which is a good leaving group. Allows NH3 to be added. Also deprotonates NH4+
Carbamoyl-Phosphate Synthase I reaction HCO3- + 2ATP + NH3 --> Carbamoyl phosphate in two step reaction
Benefit of using glutamine as an ammonia source NH3 can be taken from glutamine and used in a reaction without touching water, meaning NH4+ cannot be generated
Carbamoyl-Phosphate Synthase II reaction Hydrolyzes glutamine and sends the NH3 through a tunnel to be used to make carbamoyl phosphate - prevents protonation
Parts of carbamoyl phosphate synthase II Amidohydrolase site (uses -SH to hydrolyze glutamine); NH3 tunnel (moves NH3 to prevent protonation); biosynthetic site (nucelophilic reaction occurs using NH3)
Ways that nitrogen is lost from body Ammonia, uric acid, urea, creatinine
Fish are? ammonotelic (excrete ammonia)
Birds are? Uricotelic (excrete uric acid)
Mammals are? ureotelic (excrete urea) [mainly - some uric acid and creatinine]
Main site of NH3 detoxification Liver, some in kidneys
Urea overall reaction HCO3- + NH4+ + 3ATP + Aspartate + H2O --> Urea + 5H+ + Fumarate + AMP + PPi + 2ATP + 2Pi
added benefit of urea reaction releases H+, can control pH
Urea Cycle Reactions in mitochondria Ornithine transcarbamoylase (ornithine --> citrulline), Carbamoyl-Phosphate Synthase I, Glutamine Dehydrogenase for nitrogen
Urea Cycle reactions in cytoplasm Argininosuccinate Lyase, Arginiosuccinate Synthase, Arginase
Created by: CGraybosch
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