Biochemistry: Deamination and Urea Cycle
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Questions and Answers

What is the primary source of biologically useful nitrogen in our bodies?

  • Fats
  • Carbohydrates
  • Dietary proteins (correct)
  • Vegetables

    • Glutamate dehydrogenase is the only amino acid dehydrogenase with significant activity in the body.

    True

    What toxic substance is produced during the removal of nitrogen from amino acids?

    ammonia

    The conversion of ammonia to non-toxic urea mainly occurs in the _____?

    <p>liver</p> Signup and view all the answers

    Match the following amino acids with their roles in nitrogen transport:

    <p>Glutamine = Transport of ammonia to liver Alanine = Transport of ammonia to liver Aspartate = Source for ammonia production Glutamate = Primary amino acid undergoing deamination</p> Signup and view all the answers

    Which enzyme is primarily responsible for the deamination of glutamate?

    <p>Glutamate dehydrogenase</p> Signup and view all the answers

    Nitrogen is primarily excreted from the body in the form of uric acid.

    <p>False</p> Signup and view all the answers

    What process describes the transfer of amino groups from amino acids to alpha-ketoglutarate?

    <p>transamination</p> Signup and view all the answers

    High serum levels of ammonia can indicate _____ disease.

    <p>liver</p> Signup and view all the answers

    What byproducts are produced from the hydrolysis of asparagine and glutamine?

    <p>Aspartate and Glutamate</p> Signup and view all the answers

    What activates CPSI in the urea cycle?

    <p>N-acetyl glutamate</p> Signup and view all the answers

    High levels of arginine inhibit CPSI activity.

    <p>False</p> Signup and view all the answers

    What is the carrier molecule in the urea cycle?

    <p>Ornithine</p> Signup and view all the answers

    The final product of the hydrolysis of arginine by arginase is _____ and ornithine.

    <p>urea</p> Signup and view all the answers

    Match the following urea cycle reactions with their enzymes:

    <p>Citrulline formation = Ornithine transcarbamoylase Arginine to urea = Arginase Argininosuccinate formation = Argininosuccinate synthetase Fumarate elimination = Argininosuccinate lyase</p> Signup and view all the answers

    Which amino acid is specifically involved in acquiring the second nitrogen of urea?

    <p>Aspartate</p> Signup and view all the answers

    Defects in the urea cycle usually lead to low levels of ammonia in the body.

    <p>False</p> Signup and view all the answers

    What dietary condition can induce urea cycle enzymes?

    <p>High protein diet</p> Signup and view all the answers

    The ornithine/citrulline transporter is located on the _____ mitochondrial membrane.

    <p>inner</p> Signup and view all the answers

    Which of the following is NOT a characteristic of urea cycle defects?

    <p>Increased energy levels</p> Signup and view all the answers

    Which enzyme catalyzes the deamination of histidine to produce ammonia and urocanate?

    <p>Histidinase</p> Signup and view all the answers

    The purine nucleotide cycle involves the conversion of IMP to AMP.

    <p>False</p> Signup and view all the answers

    What are D-amino acids converted to in the body?

    <p>L-amino acids</p> Signup and view all the answers

    In the urea cycle, the two nitrogens in urea come from __________ and __________.

    <p>ammonia, aspartate</p> Signup and view all the answers

    Match the following enzymes with their respective functions:

    <p>Histidinase = Deamination of histidine Serine dehydratase = Dehydration of serine and threonine Glutamate dehydrogenase = Conversion of glutamate to ammonia Carbamoyl phosphate synthetase I = First step in the urea cycle</p> Signup and view all the answers

    What role does N-acetylglutamate (NAG) play in the urea cycle?

    <p>Activator of carbamoyl phosphate synthetase I</p> Signup and view all the answers

    The reaction that feeds ammonia into the urea cycle occurs in the cytosol.

    <p>False</p> Signup and view all the answers

    How many ATP molecules are used by carbamoyl phosphate synthetase I in the urea cycle?

    <p>Two</p> Signup and view all the answers

    The conversion of AMP to IMP in the purine nucleotide cycle releases __________.

    <p>ammonia</p> Signup and view all the answers

    Which of the following compounds are produced by serine and threonine dehydration?

    <p>Pyruvate and α-ketobutyrate</p> Signup and view all the answers

    Study Notes

    Deamination of Histidine

    • Histidine is deaminated by histidinase (histidine ammonia lyase) to yield ammonia and urocanate.

    Other Reactions that Produce Ammonia

    • Asparaginase and glutaminase hydrolyze the side-chain amides of asparagine and glutamine respectively to yield aspartate and glutamate.
    • Serine dehydratase catalyzes the pyridoxal-5-phosphate dependent dehydration of serine and threonine to yield pyruvate and α-ketobutyrate, and ammonia.
    • The purine nucleotide cycle operates in muscle, releasing ammonia when AMP is converted to IMP.
    • L and D amino oxidase reactions, primarily occurring in the kidney, racemize D-amino acids to L-amino acids.

    The Urea Cycle

    • The urea cycle is the primary pathway for detoxifying ammonia in the body.
    • Two nitrogen atoms in urea are derived from ammonia and aspartate, while the carbon atom comes from bicarbonate.
    • Some reactions of the urea cycle occur in the mitochondria, others in the cytosol.
    • Glutamate dehydrogenase, the enzyme that feeds ammonia into the urea cycle, is located in the mitochondria.
    • Ammonia, released from glutamate dehydrogenase, reacts with bicarbonate to form carbamoyl phosphate.
    • This reaction is catalyzed by carbamoyl phosphate synthetase I (CPS1).
    • CPS1 differs from CPSII, the cytosolic enzyme responsible for carbamoyl phosphate production for pyrimidine biosynthesis.
    • CPS1 is activated by N-acetyl glutamate (NAG), synthesized when there is extensive amino acid deamination.
    • Ornithine serves as the 'carrier' molecule in the urea cycle, reacting with carbamoyl phosphate to form citrulline.
    • Citrulline leaves the mitochondria and moves into the cytosol for further reactions in the urea cycle.
    • The second nitrogen atom in urea is acquired from aspartate in a reaction catalyzed by argininosuccinate synthetase.
    • Argininosuccinate lyase removes fumarate from argininosuccinate, resulting in arginine.
    • Arginase hydrolyzes arginine to release urea and regenerate ornithine.
    • The urea cycle is linked to glycolysis and the TCA cycle through pyruvate, oxaloacetate, α-ketoglutarate, and fumarate.

    Control of the Urea Cycle

    • The urea cycle is regulated through substrate availability, allosteric regulation of CPS1 by NAG, and induction of urea cycle enzymes.
    • Induction of urea cycle enzymes occurs in response to high protein diets, prolonged fasting, or starvation, when protein breakdown is increased.

    Defects of the Urea Cycle

    • Defects in any of the urea cycle enzymes can lead to mental retardation, seizures, coma, and early death.
    • Deficiencies in CPS1 and ornithine transcarbamoylase are particularly dangerous, often resulting in high ammonia levels.

    Removal and Disposal of Amino Acid Nitrogen

    • Deamination of amino acids results in the production of ammonia.
    • Ammonia is toxic and is converted to urea in the liver for detoxification.
    • Urea is excreted in urine.
    • Ammonia produced in tissues other than the liver is transported to the liver mainly as glutamine and alanine.
    • Liver extracts amino acids from the blood and deaminates them, producing ammonia for detoxification.
    • The primary route of amino acid deamination involves the transfer of amino groups from amino acids to α-ketoglutarate, forming glutamate (transamination).
    • Glutamate dehydrogenase removes the amino group from glutamate as ammonia through oxidative deamination.
    • Glutamate dehydrogenase is the main amino acid dehydrogenase active in the body.

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    Amino Acid Metabolism Lecture Notes PDF

    Description

    This quiz covers key concepts related to the deamination of amino acids, including histidine and other reactions producing ammonia. It also explores the urea cycle's role in detoxifying ammonia in the body and its various biochemical pathways. Test your knowledge of these fundamental biochemical processes.

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