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Questions and Answers
Where does the urea cycle primarily take place?
Where does the urea cycle primarily take place?
Which molecule is formed when ammonia reacts with carbon dioxide and ATP?
Which molecule is formed when ammonia reacts with carbon dioxide and ATP?
Which enzyme is involved in the reaction where carbamoyl phosphate is formed?
Which enzyme is involved in the reaction where carbamoyl phosphate is formed?
Which metabolic pathway is responsible for removing ammonia from the body?
Which metabolic pathway is responsible for removing ammonia from the body?
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What is the primary function of the urea cycle in the body?
What is the primary function of the urea cycle in the body?
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Which enzyme is primarily responsible for the conversion of glutamate and ammonia into glutamine?
Which enzyme is primarily responsible for the conversion of glutamate and ammonia into glutamine?
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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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What is the main transport form of ammonia in the circulation?
What is the main transport form of ammonia in the circulation?
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Hyperammonemia is most directly caused by:
Hyperammonemia is most directly caused by:
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Which symptom is NOT associated with ammonia intoxication?
Which symptom is NOT associated with ammonia intoxication?
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Which of the following correctly describes the fate of urea in the body?
Which of the following correctly describes the fate of urea in the body?
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Which condition can lead to hyperammonemia due to genetic defects?
Which condition can lead to hyperammonemia due to genetic defects?
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What is the primary mechanism for the removal of ammonia in the brain?
What is the primary mechanism for the removal of ammonia in the brain?
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Which of the following processes does NOT contribute to the production of the amino acid pool?
Which of the following processes does NOT contribute to the production of the amino acid pool?
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What enzyme mediates the oxidative deamination of glutamate to α-ketoglutarate and NH3?
What enzyme mediates the oxidative deamination of glutamate to α-ketoglutarate and NH3?
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What regulates protein turnover involving the amino acid pool?
What regulates protein turnover involving the amino acid pool?
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Which molecule is formed as a result of the activity of aminotransferases?
Which molecule is formed as a result of the activity of aminotransferases?
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Which of the following is a direct consequence of inherited enzyme deficiencies related to nitrogen metabolism?
Which of the following is a direct consequence of inherited enzyme deficiencies related to nitrogen metabolism?
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Accumulation of what substance can be an indicator of liver damage?
Accumulation of what substance can be an indicator of liver damage?
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Where does the degradation of body protein typically occur?
Where does the degradation of body protein typically occur?
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What nitrogen-containing substance is incorporated into urea along with CO2?
What nitrogen-containing substance is incorporated into urea along with CO2?
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What is the primary route for disposing of nitrogen from the body?
What is the primary route for disposing of nitrogen from the body?
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What is a common cause of hyperammonemia in adults?
What is a common cause of hyperammonemia in adults?
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Which enzyme deficiency is most commonly associated with congenital hyperammonemia?
Which enzyme deficiency is most commonly associated with congenital hyperammonemia?
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How is liver cirrhosis related to hyperammonemia?
How is liver cirrhosis related to hyperammonemia?
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Which inheritance pattern do most urea cycle disorders follow?
Which inheritance pattern do most urea cycle disorders follow?
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What compound is phenylbutyrate converted to after oral administration?
What compound is phenylbutyrate converted to after oral administration?
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What is the result of shunting portal blood directly into systemic circulation in liver disease?
What is the result of shunting portal blood directly into systemic circulation in liver disease?
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Which of the following amino acids is associated with less severe symptoms in urea cycle disorders due to its ability to contain two waste nitrogens?
Which of the following amino acids is associated with less severe symptoms in urea cycle disorders due to its ability to contain two waste nitrogens?
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Which enzyme system is responsible for ATP-independent degradation of proteins in cells?
Which enzyme system is responsible for ATP-independent degradation of proteins in cells?
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What is a treatment strategy for urea cycle defects that has improved survival rates?
What is a treatment strategy for urea cycle defects that has improved survival rates?
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What form do fatty acids take when stored in adipose tissue?
What form do fatty acids take when stored in adipose tissue?
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Why do TAGs provide concentrated stores of metabolic energy?
Why do TAGs provide concentrated stores of metabolic energy?
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How much energy is yielded from the complete oxidation of fatty acids to CO2 and H2O?
How much energy is yielded from the complete oxidation of fatty acids to CO2 and H2O?
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How does the energy yield from fatty acids compare to that from proteins or carbohydrates?
How does the energy yield from fatty acids compare to that from proteins or carbohydrates?
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What characteristic of TAGs makes them an efficient form of energy storage in the body?
What characteristic of TAGs makes them an efficient form of energy storage in the body?
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Which factor increases the melting temperature of a fatty acid?
Which factor increases the melting temperature of a fatty acid?
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Which fatty acid is represented by the structure 18:3(9,12,15)?
Which fatty acid is represented by the structure 18:3(9,12,15)?
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What characterizes a saturated fatty acid chain?
What characterizes a saturated fatty acid chain?
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What is the precursor of ω-6 arachidonic acid?
What is the precursor of ω-6 arachidonic acid?
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Which fatty acid deficiency can lead to scaly dermatitis and neurologic abnormalities?
Which fatty acid deficiency can lead to scaly dermatitis and neurologic abnormalities?
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Which statement is true about an ω-3 fatty acid?
Which statement is true about an ω-3 fatty acid?
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Which fatty acid has the structure 20:4(5,8,11,14)?
Which fatty acid has the structure 20:4(5,8,11,14)?
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Which fatty acid is not found in significant quantities in milk?
Which fatty acid is not found in significant quantities in milk?
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In the transamination reaction involving oxaloacetate and glutamate, what amino acid is formed from oxaloacetate?
In the transamination reaction involving oxaloacetate and glutamate, what amino acid is formed from oxaloacetate?
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Which of the following statements about the urea cycle is correct regarding the nitrogen sources?
Which of the following statements about the urea cycle is correct regarding the nitrogen sources?
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An increase in which of the following would most strongly indicate a defect in the enzyme argininosuccinate lyase?
An increase in which of the following would most strongly indicate a defect in the enzyme argininosuccinate lyase?
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Which enzyme's deficiency would most likely result in elevated urinary orotic acid levels?
Which enzyme's deficiency would most likely result in elevated urinary orotic acid levels?
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In a patient with argininosuccinate synthetase deficiency, which substrate would accumulate?
In a patient with argininosuccinate synthetase deficiency, which substrate would accumulate?
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The hydrolysis of which amino acid directly produces urea in the urea cycle?
The hydrolysis of which amino acid directly produces urea in the urea cycle?
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Which one of the following pairs is not correctly matched in terms of amino acid and corresponding α-keto acid?
Which one of the following pairs is not correctly matched in terms of amino acid and corresponding α-keto acid?
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Which enzyme in the urea cycle is associated with both the mitochondria and the cytosol?
Which enzyme in the urea cycle is associated with both the mitochondria and the cytosol?
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What role do plasma free fatty acids primarily serve?
What role do plasma free fatty acids primarily serve?
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At physiologic pH, the terminal carboxyl group of a fatty acid ionizes to become which functional group?
At physiologic pH, the terminal carboxyl group of a fatty acid ionizes to become which functional group?
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What percentage of fatty acids found in the plasma are in the form of fatty acid esters?
What percentage of fatty acids found in the plasma are in the form of fatty acid esters?
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Which intracellular molecules attach to fatty acids to enhance the ability of proteins to associate with membranes?
Which intracellular molecules attach to fatty acids to enhance the ability of proteins to associate with membranes?
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What component is NOT mentioned as part of the triacylglycerol synthesis and degradation pathway?
What component is NOT mentioned as part of the triacylglycerol synthesis and degradation pathway?
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During fasting, where can substantial amounts of free fatty acids be found?
During fasting, where can substantial amounts of free fatty acids be found?
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What term best describes the nature of a long-chain fatty acid?
What term best describes the nature of a long-chain fatty acid?
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Which of the following serves as a major energy reserve in the body?
Which of the following serves as a major energy reserve in the body?
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Which component provides the nitrogen atom that is incorporated into urea during the urea cycle?
Which component provides the nitrogen atom that is incorporated into urea during the urea cycle?
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What is the immediate precursor of both ammonia and aspartate nitrogen in the urea cycle?
What is the immediate precursor of both ammonia and aspartate nitrogen in the urea cycle?
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Which enzyme requires N-Acetylglutamate as an essential activator in the urea cycle?
Which enzyme requires N-Acetylglutamate as an essential activator in the urea cycle?
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How many high-energy phosphate bonds are consumed in the synthesis of each molecule of urea?
How many high-energy phosphate bonds are consumed in the synthesis of each molecule of urea?
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Following the ingestion of a protein-rich meal, what happens to the intrahepatic concentration of N-acetylglutamate?
Following the ingestion of a protein-rich meal, what happens to the intrahepatic concentration of N-acetylglutamate?
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Which metabolic intermediates link to produce ammonia, essential for the movement of nitrogen from peripheral tissues to the liver?
Which metabolic intermediates link to produce ammonia, essential for the movement of nitrogen from peripheral tissues to the liver?
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What is the role of renal glutaminase in the metabolism of ammonia?
What is the role of renal glutaminase in the metabolism of ammonia?
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Which of the following correctly represents the overall stoichiometry of the urea cycle?
Which of the following correctly represents the overall stoichiometry of the urea cycle?
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What initiates the hydrolytic release of fatty acids from triacylglycerol (TAG)?
What initiates the hydrolytic release of fatty acids from triacylglycerol (TAG)?
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Which enzyme phosphorylates hormone-sensitive lipase to activate it?
Which enzyme phosphorylates hormone-sensitive lipase to activate it?
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What molecule binds to receptors on the adipocyte cell membrane to activate adenylyl cyclase?
What molecule binds to receptors on the adipocyte cell membrane to activate adenylyl cyclase?
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Why can't glycerol released during TAG degradation be metabolized by adipocytes?
Why can't glycerol released during TAG degradation be metabolized by adipocytes?
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Which metabolic pathway can dihydroxyacetone phosphate (DHAP) participate in?
Which metabolic pathway can dihydroxyacetone phosphate (DHAP) participate in?
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Which tissue types cannot use plasma free fatty acids (FFA) for fuel?
Which tissue types cannot use plasma free fatty acids (FFA) for fuel?
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Which process reduces plasma free fatty acids (FFA) to mitigate insulin resistance?
Which process reduces plasma free fatty acids (FFA) to mitigate insulin resistance?
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What do long-chain fatty acids (LCFA) convert to in the cytosol after entering a cell for beta-oxidation?
What do long-chain fatty acids (LCFA) convert to in the cytosol after entering a cell for beta-oxidation?
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Study Notes
Metabolism of Ammonia
- Ammonia is a by-product of protein metabolism, produced in the body from the breakdown of amino acids, purines, and pyrimidines.
- Ammonia is detoxified in the liver to urea and excreted by the kidneys.
- Sources of ammonia include:
- Intestinal glutamine metabolism
- Bacterial action in the intestine
- Amino acids
- Purines and pyrimidines
- Transport of ammonia in the circulation:
- Urea is the main disposal route for ammonia, traveling from the liver to the kidneys.
- Glutamine serves as a non-toxic storage and transport form of ammonia.
Hyperammonemia
- Occurs when the capacity of the hepatic urea cycle is exceeded, leading to elevated serum ammonia levels.
- Can also occur when liver function is compromised, such as in liver disease or genetic defects of the urea cycle.
- Hyperammonemia can cause a direct neurotoxic effect on the CNS.
- Symptoms of ammonia intoxication include:
- Tremors
- Slurring of speech
- Somnolence
- Vomiting
- Cerebral edema
- Blurring of vision
- At high concentrations, ammonia can cause coma and death.
Urea Cycle
- The urea cycle is a metabolic pathway that removes ammonia from the body.
- It takes place in the liver and is a cyclic process.
- The overall stoichiometry of the urea cycle is:
- Aspartate + NH3 + CO2 + 3 ATP + H2O → urea + fumarate + 2 ADP + AMP + 2 P + PP
- Regulation of the urea cycle involves N-acetylglutamate, which is an essential activator for carbamoyl phosphate synthetase I.
Fatty Acid and Triacylglycerol Metabolism
- Fatty acids exist in a free and unesterified form or as fatty acyl esters in more complex molecules.
- Fatty acids are stored in adipose tissue in the form of neutral triacylglycerols (TAGs).
- Mobilization of stored fat requires hydrolytic release of fatty acids and glycerol from their TAG form.
- Release of fatty acids from TAG is initiated by hormone-sensitive lipase.
- Activation of hormone-sensitive lipase involves phosphorylation by a 3'5'-cyclic AMP (cAMP)-dependent protein kinase.
B-Oxidation of Fatty Acids
- The major pathway for catabolism of fatty acids is a mitochondrial pathway called B-oxidation.
- In B-oxidation, two-carbon fragments are successively removed from the carboxyl end of the fatty acyl CoA, producing acetyl CoA, NADH, and FADH2.
- Transport of long-chain fatty acids (LCFA) into the mitochondria involves conversion to their CoA derivative by long-chain fatty acyl CoA synthetase (thiokinase).
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Description
Ammonia is a by-product of protein metabolism, produced in the body from amino acids, purines, and pyrimidines, and detoxified in the liver to urea and excreted by the kidneys.
