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The Urea Cycle quiz

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  • What is the main function of the urea cycle?
    The urea cycle converts toxic ammonium ion into urea for safe excretion, using ornithine as a carrier.
  • Which molecules provide the nitrogen atoms for urea synthesis in the urea cycle?
    The nitrogen atoms come from ammonium ion and aspartate.
  • How many ATP molecules are consumed in the urea cycle?
    A total of four ATP molecules are consumed during the urea cycle.
  • What is the carbon source for urea in the urea cycle?
    The carbon source is carbon dioxide, which originates from the mitochondrial matrix.
  • What enzyme catalyzes the synthesis of carbamoyl phosphate in Phase A of the urea cycle?
    Carbamoyl phosphate synthetase catalyzes this reaction.
  • What are the substrates and products of the first reaction in Phase B of the urea cycle?
    Carbamoyl phosphate and ornithine are substrates, and citrulline is the product.
  • Which enzyme catalyzes the transfer of the carbamoyl group to ornithine?
    Ornithine transcarbamylase (OTC) catalyzes this transfer.
  • What reaction occurs when citrulline condenses with aspartate, and which enzyme catalyzes it?
    Citrulline condenses with aspartate to form argininosuccinate, catalyzed by argininosuccinate synthetase.
  • What are the products of the cleavage of argininosuccinate?
    The products are arginine and fumarate.
  • Which enzyme catalyzes the cleavage of argininosuccinate?
    Argininosuccinase (also called argininosuccinate lyase) catalyzes this reaction.
  • What happens to arginine in the final step of the urea cycle?
    Arginine is hydrolyzed by arginase to produce ornithine and urea.
  • What is the fate of ornithine after the urea cycle is completed?
    Ornithine is regenerated and transported back to the mitochondrial matrix to start another cycle.
  • What mnemonic helps remember the order of metabolites in the urea cycle?
    'Ordinary carpooling citizen aspires arranged success fuels arguments utters opinions' helps recall the metabolites.
  • What mnemonic helps remember the reaction types and enzymes in the urea cycle?
    'Train conductor cleans house' helps recall transfer, condensation, cleavage, and hydrolysis reactions and their enzymes.
  • Where do the four main reactions of Phase B in the urea cycle occur within the cell?
    The first reaction occurs in the mitochondrial matrix, while the remaining three occur in the cytosol.