Week 13: Protein Turnover and The Urea Cycle

An infant starts to show signs of lethargy rapidly after birth. Upon evaluation, he is determined to have a deficiency in N-acetyl glutamate synthetase. Based on this information, which of the following would be consistent with this diagnosis?
- Elevated levels of arginine
- Decreased levels of ammonia
- Elevated levels of citrulline
- Decreased levels of carbamoyl phosphate

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Terms in this set (8)

- Decreased levels of carbamoyl phosphate

Explain why metabolic defects in different enzymes of urea biosynthesis, although distinct at the molecular level, present similar clinical signs and symptoms. Describe both the classical approaches in screening neonates for inherited metabolic diseases,

Consider the reaction shown below. Which stage of urea biosynthesis does the figure highlight?
- Polyglutamation
- Ammonia transport
- Transamination
- Urea cycle
- Oxidative deamination of glutamate

- Transamination

Describe the reactions that convert NH3, CO2, and the amide nitrogen of aspartate into urea, and identify the subcellular locations of the enzymes that catalyze urea biosynthesis.

Glutamate can be deaminated by which of the following enzymes:
- Glutaminase
- Glutamine synthetase
- Glutamate dehydrogenase (GDH)
- Arginase

- Glutamate dehydrogenase (GDH)

Illustrate the central roles of transaminases (aminotransferases), of glutamate dehydrogenase, glutamine synthetase, and of glutaminase in human nitrogen metabolism

A deficiency in which of the following enzymes will not result in an increase in orotic acid?
- Ornithine transcarbamylase
- N-acetyl glutamate synthetase
- Argininosuccinate lyase
- Argininosuccinate synthetase

- N-acetyl glutamate synthetase

Explain why metabolic defects in different enzymes of urea biosynthesis, although distinct at the molecular level, present similar clinical signs and symptoms.

Which of the following enzymes is regulated by N-acetyl glutamate (NAG)?
- Argininosuccinate lyase
- Carbamoyl phosphate synthetase I (CPS I)
- Ornithine transcarbamylase
- Carbamoyl phosphate synthetase II (CPS II)

- Carbamoyl phosphate synthetase I (CPS I)

Describe the reactions that convert NH3, CO2, and the amide nitrogen of aspartate into urea, and identify the subcellular locations of the enzymes that catalyze urea biosynthesis.

The reaction of ammonia with α-ketoglutarate is catalyzed by _________ and requires _________ as a reactant.
- glutamate dehydrogenase; NADH or NADPH
- glutamate synthetase; ATP
- glutamate synthetase; NADH or NADPH
- glutamate dehydrogenase; ATP

- glutamate dehydrogenase; NADH or NADPH

Illustrate the central roles of transaminases (aminotransferases), of glutamate dehydrogenase, glutamine synthetase, and of glutaminase in human nitrogen metabolism.

Which of the following enzymes is correctly paired with its activator?
- Carbamoyl phosphate synthetase I; ATP
- Glutaminase; citrate
- N-acetyl glutamate synthetase; arginine
- arginase; NADH

- N-acetyl glutamate synthetase; arginine

Indicate the roles of allosteric regulation and of acetyl-glutamate in the regulation of the earliest steps in urea biosynthesis.

Which of the following statements is consistent with protein catabolism in the fed state?
- High levels of arginine will stimulate the activity of urea synthesis
- The conversion of alpha-ketoglutarate to glutamate will be favored in the liver
- Amino acids will be used as a substrate for gluconeogenesis
- Glutaminase activity in the liver will be low

- High levels of arginine will stimulate the activity of urea synthesis

Describe the reactions that convert NH3, CO2, and the amide nitrogen of aspartate into urea, and identify the subcellular locations of the enzymes that catalyze urea biosynthesis.