Question | Answer |
Where is urea synthesized? | liver |
What is the structure of urea? | 2 amino groups attached to a central carbonyl group |
Where do the parts of urea come from? | Carbonyl derived from CO2, 1 N-atom from aspartate (asp) the other from ammonium |
Where does Urea synthesis begin and end within the cell? | Mitochondria to start, cytoplasm to finish |
How much energy is required to run the urea cycle? | 4 ATPs |
What is the crucial, rate limiting first enzyme for urea synthesis (found in mitochondria)? | carbamoyl phosphate |
What is the second enzyme of the urea cycle? Also rate limiting | Ornithine transcarbamoylase condenses carbamoyl phosphate with ornithine to form citruline |
The most common genetic defiencies in urea cycle are associated with what? | the two enzymes: carbamoyl phosphate & ornithine transcarbamoylase |
What does arginase do in the urea cycle? Where? | cleaves arginine into urea and ornithine (which is recycled. |
Where does apspartate occur in the urea cycle? | It enters in the cytoplasm to convert citrulline to argininosuccinate which cleaves to form fumarate and arginine by a lyase. |
Is all the arginine required available via urea synthesis? | No, most comes from diet. |
What happens with CPS-1 and Ornithine transcarbamoylase deficiency? | Hyperammonenemia; Decrease in BUN (Blood Urea Nitrogen, Cerebral edema;lethargy, convulsion, coma, death |
What is the difference between Aspartate and Fumarate? | fumarate does not have the amino group |
Where does fumarate go following the urea cycle? | It can enter the TCA for energy or gluconeogenesis |
Where does urea go from the kidney? | Transported by blood to the kidney |
What is the famous phrase regarding the urea cycle? | Better to be pissed off, than pissed on |