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Questions and Answers
What is the primary function of the urea cycle in the liver?
What is the primary function of the urea cycle in the liver?
Which of the following conditions can lead to acquired hyperammonemia?
Which of the following conditions can lead to acquired hyperammonemia?
What is the main symptom associated with inherited hyperammonemia?
What is the main symptom associated with inherited hyperammonemia?
How does ammonia intoxication affect the citric acid cycle?
How does ammonia intoxication affect the citric acid cycle?
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Which of the following is NOT a direct consequence of hyperammonemia in the brain?
Which of the following is NOT a direct consequence of hyperammonemia in the brain?
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What is the normal range for plasma urea concentration in milligrams per deciliter (mg/dl)?
What is the normal range for plasma urea concentration in milligrams per deciliter (mg/dl)?
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Which of the following is NOT an amino acid involved in the urea cycle?
Which of the following is NOT an amino acid involved in the urea cycle?
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What is the primary site of urea formation in the body?
What is the primary site of urea formation in the body?
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Which of the following is NOT a product of the catabolism of α-ketoacids?
Which of the following is NOT a product of the catabolism of α-ketoacids?
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What is the role of N-acetyl glutamate in the urea cycle?
What is the role of N-acetyl glutamate in the urea cycle?
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Where does the formation of citrulline take place in the urea cycle?
Where does the formation of citrulline take place in the urea cycle?
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What is the fate of ornithine in the urea cycle?
What is the fate of ornithine in the urea cycle?
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Which of the following molecules is NOT directly involved in the formation of carbamoyl phosphate?
Which of the following molecules is NOT directly involved in the formation of carbamoyl phosphate?
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What is the primary function of the urea cycle?
What is the primary function of the urea cycle?
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Which of the following statements accurately describes the role of α-ketoglutarate in the fate of α-ketoacids?
Which of the following statements accurately describes the role of α-ketoglutarate in the fate of α-ketoacids?
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How many ATP molecules are used in the formation of carbamoyl phosphate?
How many ATP molecules are used in the formation of carbamoyl phosphate?
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What is the primary toxic effect of ammonia on the body?
What is the primary toxic effect of ammonia on the body?
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Which amino acid is primarily involved in transporting ammonia from peripheral tissues to the liver?
Which amino acid is primarily involved in transporting ammonia from peripheral tissues to the liver?
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What enzyme is responsible for the formation of ammonia from glutamine in the kidneys?
What enzyme is responsible for the formation of ammonia from glutamine in the kidneys?
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Ammonia can be produced in the intestine by the action of bacterial enzymes on which of the following?
Ammonia can be produced in the intestine by the action of bacterial enzymes on which of the following?
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Which function of glutamine helps in the detoxification of ammonia in the brain?
Which function of glutamine helps in the detoxification of ammonia in the brain?
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What is the fate of ammonia after it is produced in the body?
What is the fate of ammonia after it is produced in the body?
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What is the normal concentration range of ammonia in blood?
What is the normal concentration range of ammonia in blood?
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Which of the following is NOT a source of ammonia in the body?
Which of the following is NOT a source of ammonia in the body?
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Study Notes
Ammonia (NH3)
- Ammonia is a toxic substance, especially to the central nervous system, and must be converted into urea in the liver.
- Ammonia is transported from peripheral tissues to the liver via:
- Glutamine (most tissues)
- Alanine (muscle)
- Blood contains traces of ammonia (10-80 ug/dL).
- Sources of ammonia include:
- Transdeamination of amino acids (mainly in liver)
- Glutamine metabolism (kidneys)
- Purines and pyrimidines metabolism
- Intestinal bacteria action on dietary amino acids and urea
Fate of Ammonia
- Formation of non-essential amino acids through transdeamination
- Formation of glutamine:
- Glutamine synthetase is a mitochondrial enzyme present in many tissues (kidney, brain)
- Glutamine functions:
- Regulation of acid-base balance
- Removes toxic effect of ammonia in brain
- Source of N3 and N9 of purines bases
- Used in detoxication of phenyl acetic acid
- Formation of urea
- Excretion in urine
Ammonia Intoxication
- Definition: Excess ammonia toxic to the central nervous system
- Symptoms:
- Flapping tremors, slurring speech, blurring vision, and vomiting in infancy
- High concentration of ammonia can cause coma and death
- Types and causes of hyperammonemia:
- Acquired hyperammonemia:
- Liver cell failure
- Renal failure
- Shunt operation between portal and systemic circulation
- Collaterals between portal and systemic circulation (cirrhosis, hepatitis)
- Inherited hyperammonemia:
- Genetic deficiency of one of five enzymes of urea cycle
- Acquired hyperammonemia:
- Mechanism of ammonia intoxication:
- Ammonia reacts with α-Ketoglutarate by glutamate dehydrogenase enzyme
- Depletes α-Ketoglutarate, leading to decrease in ATP and energy production
- Symptoms of ammonia intoxication and coma
Urea
- Urea is the main end product of protein metabolism
- Urea formation is the pathway through which the liver converts toxic ammonia into non-toxic urea
- Site of urea formation:
- Liver is the only site for urea formation
- Urea is transported in blood to the kidney to be excreted in urine
- Plasma urea:
- Normal level: 15-45 mg/dL
- Diagnostic importance: measures kidney function, high levels indicate kidney disease (uremia)
Urea Formation (Krebs' Henseleit Cycle)
- The first two reactions occur in mitochondria, others in cytosol
- Six amino acids involved: ornithine, citrulline, arginosuccinate, Aspartate, Arginine, and N-acetyl glutamate
- Steps:
- Formation of Carbamoyl phosphate:
- Occurs in mitochondria
- Needs CO2, ammonia, phosphate, and ATP
- Catalyzed by Carbamoyl phosphate synthase I
- Formation of citrulline:
- Occurs in mitochondria
- Carbamoyl phosphate reacts with ornithine
- Formation of arginosuccinate:
- Citrulline reacts with Aspartate in cytosol
- Cleavage of arginosuccinate:
- Into Arginine and Fumarate
- Cleavage of Arginine into ornithine and urea:
- Ornithine passes back to mitochondria
- Urea passes to blood to be excreted by kidney in urine
- Formation of Carbamoyl phosphate:
Fate of α-Keto-Acids
- The α-ketoacid remaining after transamination and deamination of amino acids may undergo:
- Reamination by ammonia to form the corresponding amino acid
- Catabolized to form seven products:
- Pyruvate
- Acetyl CoA
- Acetoacetyl CoA
- Fumarate
- Oxaloacetate
- α-Ketoglutarate
- Succinyl CoA
- These products enter different pathways leading to:
- Synthesis of glycogen or glucose
- Synthesis of lipids
- Complete oxidation into CO2 and H2O
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Description
This quiz covers the metabolism of ammonia, its toxicity, and its conversion to urea in the liver. It's part of a biochemistry course taught by Dr. Wael Sobhy Darwish.