15 Questions
Which organ is the only site for urea formation in the body?
Liver
In which organelle do the first two reactions of the urea cycle occur?
Mitochondria
Which molecule is used to provide phosphate in the synthesis of carbamoylphosphate in the urea cycle?
ATP
From which compound is the first nitrogen atom in urea derived in the urea cycle?
Ammonia
What is the diagnostic importance of blood urea measurement?
Assessment of renal function
How many ATP molecules and high-energy phosphate bonds are utilized in the urea cycle reactions?
3 ATP molecules and 4 high-energy phosphate bonds
What is the key enzyme of the urea cycle?
Carbamoyl phosphate synthetase I
What stimulates the synthesis of N-acetylglutamate, an allosteric activator of carbamoyl phosphate synthetase I?
High protein diet
Which of the following may cause coma and death due to high concentrations of ammonia?
Flapping tremors
Which enzyme deficiency leads to hyperammonemia type II, an X-linked inherited disease?
Ornithine carbamoyl transferase
What is the treatment for argininemia, a condition caused by deficiency of arginase?
Low protein diet
7
Depletion of alpha-ketoglutarate of Krebs' cycle
What is a characteristic symptom of hyperammonemia?
Flapping tremors
What may stimulate the excretion of citrulline, thereby alleviating citrullinemia?
Increased intake of arginine
What is the main cause of inherited hyperammonemia?
Genetic deficiency of one of the five enzymes of the urea cycle
Study Notes
Urea Cycle
- The liver is the only site for urea formation in the body.
Urea Cycle Reactions
- The first two reactions of the urea cycle occur in the mitochondrial matrix.
- The molecule ATP is used to provide phosphate in the synthesis of carbamoylphosphate in the urea cycle.
Nitrogen Source
- The first nitrogen atom in urea is derived from ammonia (NH3) in the urea cycle.
Blood Urea Measurement
- Blood urea measurement is diagnostically important.
Energy Requirements
- 3 ATP molecules and 2 high-energy phosphate bonds are utilized in the urea cycle reactions.
Key Enzyme
- Carbamoyl phosphate synthetase I is the key enzyme of the urea cycle.
Regulation of Carbamoyl Phosphate Synthetase I
- N-acetylglutamate, an allosteric activator of carbamoyl phosphate synthetase I, is synthesized in response to arginine, ornithine, or glucagon.
Hyperammonemia
- High concentrations of ammonia can cause coma and death.
- Hyperammonemia type II, an X-linked inherited disease, is caused by a deficiency of ornithine transcarbamylase.
- Argininemia, a condition caused by a deficiency of arginase, can be treated with a low-protein diet and supplementation with citrulline and arginine.
- A characteristic symptom of hyperammonemia is vomiting.
- The excretion of citrulline can be stimulated by supplementation with citrulline, which alleviates citrullinemia.
- Inherited deficiencies of enzymes involved in the urea cycle are the main cause of inherited hyperammonemia.
Test your knowledge on urea cycle and blood urea levels with this quiz. Learn about the site of urea formation, diagnostic importance of blood urea, and related concepts.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
