Amino Acids I: Catabolism of Amino Acids, C Skeleton, and the Urea Cycle (Easy)

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Questions and Answers

What is the defect in the gene that causes Hyperargininemia?

Argininosuccinate lyase

Arginase (correct)

N-acetylglutamate synthase

Ornithine translocase

What is the function of the urea cycle?

To produce functional products

To remove toxic compounds from the body (correct)

To produce ornithine

To regulate ammonia production

What is the relationship between the rate of ammonia production and the rate of urea production?

The rate of ammonia production is always higher

They are directly related (correct)

They are inversely related

They are not related at all

What is the diagnosis of argininosuccinate lyase deficiency based on?

Measurement of erythrocyte argininosuccinate lyase activity Signup and view all the answers

What is the primary symptom of Carbamoyl Phosphate Synthase I Deficiency?

Irritability Signup and view all the answers

What is the role of NAG in the regulation of the urea cycle?

Production of ornithine Signup and view all the answers

What is the primary molecule that accumulates in Ornithine Permease Deficiency?

Ornithine Signup and view all the answers

What is the enzyme that is deficient in N-acetylglutamate Synthase Deficiency?

N-acetylglutamate Synthase Signup and view all the answers

What is the primary characteristic of Urea Cycle Enzyme Deficiencies?

Accumulation of amino acids Signup and view all the answers

What is the primary symptom of Arginase Deficiency?

Leg stiffness Signup and view all the answers

Asparagine is required in which process?

Tumor growth Signup and view all the answers

Which enzyme is responsible for the conversion of L-glutamate to α-ketoglutarate?

Transaminase Signup and view all the answers

What is the result of a block at glutamate γ-semialdehyde dehydrogenase?

Type 2 hyperprolinemia Signup and view all the answers

Which amino acid is associated with gyrate atrophy of the choroid and retina?

α-Ketoglutarate Signup and view all the answers

What is the metabolic defect associated with folic acid deficiency?

Accumulation of Figlu Signup and view all the answers

Which enzyme deficiency is characterized by the inability to import cytosolic ornithine into the mitochondrial matrix?

Ornithine Permease Signup and view all the answers

Which of the following is NOT a characteristic of Ornithine Transcarbamoylase deficiency?

Autosomal recessive inheritance Signup and view all the answers

What is the primary characteristic of Argininosuccinate Synthase deficiency?

25-fold elevated Km for citrulline Signup and view all the answers

Which of the following is NOT a Urea Cycle Enzyme Deficiency?

Phenylketonuria Signup and view all the answers

What is the common finding in all Urea Cycle Enzyme Deficiencies?

Hyperammonemia Signup and view all the answers

What is the product of the cleavage of argininosuccinate by argininosuccinate lyase?

Arginine and fumarate Signup and view all the answers

What is the source of nitrogen in the urea cycle?

L-aspartate and ammonia Signup and view all the answers

What is the role of arginase in the urea cycle?

Catalyzes the hydrolytic cleavage of arginine Signup and view all the answers

What is the rate-limiting enzyme in the urea cycle?

Carbamoyl phosphate synthetase Signup and view all the answers

What is the product of the reaction catalyzed by argininosuccinate synthetase?

Argininosuccinate and ATP Signup and view all the answers

Which of the following is a characteristic of Urea Cycle Enzyme Deficiencies?

Similar clinical signs and symptoms Signup and view all the answers

What is the role of N-acetylglutamate synthase in the urea cycle?

Catalyzes the formation of acetyl CoA and glutamate Signup and view all the answers

What is the primary molecule that accumulates in Ornithine Translocase Deficiency?

Ornithine Signup and view all the answers

What is the enzyme that is deficient in Carbamoyl Phosphate Synthase I Deficiency?

Carbamoyl Phosphate Synthase I Signup and view all the answers

What is the primary symptom of Arginase Deficiency?

Hyperargininemia Signup and view all the answers

What is the diagnosis of N-acetylglutamate Synthase Deficiency based on?

Clinical features and enzyme assay Signup and view all the answers

What is the relationship between urea cycle enzyme deficiencies and ammonia production?

Urea cycle enzyme deficiencies increase ammonia production Signup and view all the answers

What is the primary treatment for Urea Cycle Enzyme Deficiencies?

Dietary restriction of protein Signup and view all the answers

What is the defect in Carbamoyl Phosphate Synthase I Deficiency?

Defect in CPS1 enzyme Signup and view all the answers

What is the initial reaction in the catabolism of arginine?

Conversion to ornithine Signup and view all the answers

What is the enzyme responsible for the conversion of ornithine to glutamate-γ-semialdehyde?

Ornithine δ-Aminotransferase Signup and view all the answers

What is the condition associated with mutations of the ornithine aminotransferase?

Gyrate atrophy of the choroid plexus and retina Signup and view all the answers

What is the treatment for gyrate atrophy of the choroid plexus and retina?

Restriction of dietary arginine Signup and view all the answers

What is the result of a defective mitochondrial ornithine-citrulline antiporter?

Hyperornithinemia-hyperammonemia syndrome Signup and view all the answers

Study Notes

Argininosuccinate Lyase and Argininosuccinic Aciduria

Elevated levels of argininosuccinate found in blood, cerebrospinal fluid (CSF), and urine.
Symptoms include friable tufted hair or trichorrhexis nodosa.
Diagnosis achieved through erythrocyte argininosuccinate lyase activity measurement.
Detection can be performed using umbilical cord or amniotic fluid samples.

Arginase and Hyperargininemia

Autosomal recessive disorder linked to arginase gene mutations.
Common symptom onset between ages 2-4 years.
Blood and CSF show elevated arginine levels.
Characteristic urinary amino acid pattern indicating lysine-cystinuria.

Urea Cycle and Regulation

Urea cycle functions as a disposal pathway for toxic compounds.
Production of ammonia increases the rate of urea synthesis, showing a direct relationship.
Feedforward and feedback regulation control the urea cycle, ensuring urea removal.
N-acetylglutamate (NAG) acts as a crucial cofactor for carbamoyl phosphate synthase activity.

Enzyme Defects and Accumulating Molecules

Carbamoyl Phosphate Synthase I: Causes hyperammonemia type 1; leads to irritability, vomiting, and ataxia.
N-Acetylglutamate Synthase: NAG deficiency mirrors carbamoyl phosphate synthase defects.
Ornithine Permease: Causes hyperornithinemia-hyperammonemia-homocitrullinuria (HHH syndrome); involves mutation of the ORNT1 gene.
Ornithine Transcarbamylase: X-linked deficiency; presents with hyperammonemia type 2 and a tendency for dietary aversion to protein.
Argininosuccinate Synthetase: Results in citrullinemia; CSF and plasma levels of citrulline are significantly elevated.

Cleavage of Argininosuccinate

Cleavage forms arginine and fumarate, catalyzed by argininosuccinate lyase (or argininosuccinase).
Retention of three nitrogen atoms in arginine; fumarate converted to malate, leading to oxaloacetate.

Important Enzymes in the Urea Cycle

Five key enzymes: Carbamoyl Phosphate Synthase, Ornithine Transcarbamoylase, Argininosuccinate Synthase, Argininosuccinate Lyase, Arginase.
NAG is a cofactor for carbamoyl phosphate synthase, which is the rate-limiting enzyme of the urea cycle.
Sources of nitrogen for urea include ammonia and aspartate.

Genetic and Clinical Features

Urea cycle defects present similar symptoms; differentiation relies on laboratory findings.
Identification of accumulating intermediates aids in the diagnosis of specific enzyme deficiencies.
Therapeutic approaches center around understanding biochemistry of enzyme-related reactions.

Additional Amino Acid Defects

Asparagine and aspartate linked to essential tumor growth; defects in relevant enzymes are incompatible with life.
Deficiencies relate to specific metabolic pathways and are critical for survival.
Hyperprolinemia types 1 and 2 relate to blockages in proline metabolism, leading to distinct clinical presentations.

Summary of Patient Presentations

Presentation of urea cycle disorders often includes elevated ammonia levels.
Testing of blood and urine samples reveals specific amino acid abnormalities aiding diagnosis.
Rational therapy focuses on understanding enzyme function and managing accumulated substances.

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Amino Acids I: Catabolism of Amino Acids, C Skeleton, and the Urea Cycle (Easy)

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Questions and Answers

What is the defect in the gene that causes Hyperargininemia?

What is the function of the urea cycle?

What is the relationship between the rate of ammonia production and the rate of urea production?

What is the diagnosis of argininosuccinate lyase deficiency based on?

What is the primary symptom of Carbamoyl Phosphate Synthase I Deficiency?

What is the role of NAG in the regulation of the urea cycle?

What is the primary molecule that accumulates in Ornithine Permease Deficiency?

What is the enzyme that is deficient in N-acetylglutamate Synthase Deficiency?

What is the primary characteristic of Urea Cycle Enzyme Deficiencies?

What is the primary symptom of Arginase Deficiency?

Asparagine is required in which process?

Which enzyme is responsible for the conversion of L-glutamate to α-ketoglutarate?

What is the result of a block at glutamate γ-semialdehyde dehydrogenase?

Which amino acid is associated with gyrate atrophy of the choroid and retina?

What is the metabolic defect associated with folic acid deficiency?

Which enzyme deficiency is characterized by the inability to import cytosolic ornithine into the mitochondrial matrix?

Which of the following is NOT a characteristic of Ornithine Transcarbamoylase deficiency?

What is the primary characteristic of Argininosuccinate Synthase deficiency?

Which of the following is NOT a Urea Cycle Enzyme Deficiency?

What is the common finding in all Urea Cycle Enzyme Deficiencies?

What is the product of the cleavage of argininosuccinate by argininosuccinate lyase?

What is the source of nitrogen in the urea cycle?

What is the role of arginase in the urea cycle?

What is the rate-limiting enzyme in the urea cycle?

What is the product of the reaction catalyzed by argininosuccinate synthetase?

Which of the following is a characteristic of Urea Cycle Enzyme Deficiencies?

What is the role of N-acetylglutamate synthase in the urea cycle?

What is the primary molecule that accumulates in Ornithine Translocase Deficiency?

What is the enzyme that is deficient in Carbamoyl Phosphate Synthase I Deficiency?

What is the primary symptom of Arginase Deficiency?

What is the diagnosis of N-acetylglutamate Synthase Deficiency based on?

What is the relationship between urea cycle enzyme deficiencies and ammonia production?

What is the primary treatment for Urea Cycle Enzyme Deficiencies?

What is the defect in Carbamoyl Phosphate Synthase I Deficiency?

What is the initial reaction in the catabolism of arginine?

What is the enzyme responsible for the conversion of ornithine to glutamate-γ-semialdehyde?

What is the condition associated with mutations of the ornithine aminotransferase?

What is the treatment for gyrate atrophy of the choroid plexus and retina?

What is the result of a defective mitochondrial ornithine-citrulline antiporter?

Study Notes

Argininosuccinate Lyase and Argininosuccinic Aciduria

Arginase and Hyperargininemia

Urea Cycle and Regulation

Enzyme Defects and Accumulating Molecules

Cleavage of Argininosuccinate

Important Enzymes in the Urea Cycle

Genetic and Clinical Features

Additional Amino Acid Defects

Summary of Patient Presentations

Studying That Suits You

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