25 -Urea Cycle

Question 1

summary

deamination in liver is performed by?

Answer 1

glutaminase + glutamate Dehydrogenase

Question 2

summary

whats Carbamoyl Phosphate Synthetase-1

Answer 2

• Assimilates NH 3 to HCO 3- to generate carbamoyl-phosphate
• Rate-limiting enzyme
• Activated by NAG, which is more abundant when [glutamate] and [arginine] are high

Question 3

summary

shortly describe Urea cycle

Answer 3

1. Carbamoyl-phosphate is combined to Ornithine to generate Citrulline
2. A second NH 2 group is added coming from Aspartate
3. Urea is produced, Ornithine is regenerated.

Question 4

summary

By-products

Answer 4

• Urea is transported to the kidney for excretion in urine
• a-ketoglutarate (from GDH) and Fumarate are recycled back to the CAC
• Positive energy balance

Question 5

All the CO 2 generated during metabolism is
excreted from the body by exhalation
A. True
B. False

Answer 5

B

incorporate CO2 in urea (CPS1)

Question 6

How does the body avoid NH3 toxicity?
Select all that apply
A. Glutamine synthetase incorporates NH 3 to glutamine
B. Muscle pyruvate is converted to alanine
C. Carbamoyl-Phosphate Synthetase assimilates NH 4
D. Two NH 3 moieties are incorporated in urea, which is excreted by the kidney
E. None of the above

Answer 6

D, A, C, B

Question 7

How is urea production regulated?
Select all that apply
A. High [arginine] stimulates urea production
B. CPS-1 is downregulated in presence of NAG
C. CPS-2 downregulates CPS-1- mediated production of urea
D. CPS-1 is activated by substrate availability
E. None of the above

Answer 7

A, D

Question 8

What are the metabolic fates of the products of urea cycle? Select all that apply
A. Deamination of aspartate generates a-ketoglutarate which serves in the Citric Acid Cycle
B. Arginosuccinate generates Succinate which serves in the Citric Acid Cycle
C. Urea is exported to the kidney
D. The recycling of fumarate to the Citric Acid Cycle permits the production of NADH
E. None of the above

Answer 8

C