Urea Cycle Flashcards
Alanine and glutamine are used to carry nitrogen to the liver. What are the differences between these two transport molecules?
Alaine can only carry one nitrogen and is primarily used by muscle tissues. Glutamine can carry two nitrogen and is used by most tissues.
What enzyme removes nitrogen from glutamine in the liver?
Glutaminase
Three enzymes play a role in the transport of nitrogen via glutamine. What is the only reversible enzyme in this pathway?
Glutamate Dehydrogenase (GDH) - alpha-KG <–> glutamate
What is the role of glutamate in the transport of nitrogen via alanine?
Glutamate donates an amino group to pyruvate to synthesize alanine, becoming alpha-KG. Alpha-KG accepts an amino group from another amino acid to reproduce glutamate.
What vitamin serves as a cofactor for aminotransferase?
Vitamin B6 - PLP
What is the rate-limiting enzyme of the Urea Cycle?
Carbamoyl Phosphate Synthase I
CO2 + NH4+ + acetyl glutamate –> ornithine
Where does the Urea Cycle take place?
Mitochondria (first two steps) & Cytosol of the Liver
What enzymes of the Urea Cycle are located in the mitochondria?
Carbamoyl Phosphate Synthase I & Ornithine Transcarbamoylase
What molecules connect the Urea Cycle & TCA?
Aspartate & Fumarate
What molecule is a direct precursor of urea? What enzyme is responsible for synthesizing urea?
Arginine - Arginase I
What enzyme catalyzes the reaction between citrulline and aspartate to form argininosuccinate?
Agrinosuccinate Synthetase
What reaction in the Urea Cycle is catalyzed by Arginosuccinase?
Argininosuccinate –> Fumarate + Arginine
High levels of what three molecules are needed to push the Urea Cycle forward?
Glutamate, arginine, ammonium
What is the most severe Urea Cycle disorder? What symptoms are associated with the disorder?
Deficiency of Carbamoyl Phosphate Synthase I lethargy, seizures, increased NH4+, hyperventilation, and coma within days after birth
What is the most commonly occurring Urea Cycle disorder?
Ornithine Transcarbamoylase (OTC) Deficiency
