Flashcards in Lecture 31: Urea Cycle, Metabolic Priorities, and Diabetes Deck (81)
What is the purpose of the urea cycle?
To dispose of excess Nitrogen in the form of urea?
What is urea?
What is the only organ that can perform the urea cycle?
What is ornithine?
A 5C nonstandard AA: not used in protein synthesis, intermediate or UC
Is ornithine expended in the UC?
No it's used and then regenerated
Urea Cycle Step 1: Enzyme?
CPS I: carbamoyl phosphate synthetase I
Urea Cycle Step 1: Location?
What is the first committed step of the urea cycle?
What is the main regulatory step of the urea cycle?
Ureal Cycle Step 1a: Reactants/Products?
HCO3- + ATP => Carbonic-phosphoric acid anhydride + ADP
Ureal Cycle Step 1b: Reactants/Products?
Carbonic-phosphoric acid anhydride + NH4+ => carbamate + Pi
Ureal Cycle Step 1c: Reactants/Products?
Carbamate + ATP => carbamoyl phosphate + ADP
What is the purpose of the 2 phosphorylations occurring in Step 1 of the UC?
They prepare the substrates for nucleophilic attacks
Where does the nitrogen used in step 1 of the UC come from?
Glutamate dehydrogenase: Glutamate + H2O + NADP/NAD+ => alpha-ketoglutarate + NADPH/NADH + NH4+
What is the center of nitrogen metabolism?
What regulates CPS I? How? Why?
N-acetylglutamate by allosteric regulation because high levels represent high levels of glutamate, which mean:
1. Low gluconeogenesis because glutamate is not being used (high levels of Nitrogen in the body)
2. High alpha-ketoglutarate levels = high rate of TCA cycle
=> LOW GLUCONEOGENESIS FROM AAs
How is N-acetylglutamate formed?
N-acetylglutamate synthase: acetyl-CoA + glutamate => N-acetylglutamate
Urea Cycle Step 2: Enzyme?
Urea Cycle Step 2: Location?
Ureal Cycle Step 2: Reactants/Products?
Carbamoyl phosphate + ornithine = citrulline + Pi
Net reaction of UC step 1?
HCO3- + 2 ATP + NH3 = carbamoyl phosphate + 2 ADP + Pi
How does the UC happen in both the mitosol and the cytosol?
Ornithine and citrulline can cross the mito membrane via transporters
Urea Cycle Step 3: Enzyme?
Urea Cycle Step 3: Location?
Urea Cycle Step 3: Reactants/Products?
Citrulline + aspartate + ATP = arginino-succinate + AMP + PPi
Urea Cycle Step 4: Enzyme?
Urea Cycle Step 4: Location?
Urea Cycle Step 4: Reactants/Products?
Arginino-succinate => fumarate + arginine
Urea Cycle Step 5: Enzyme?