urea cycle converts ammonium ions to urea which is transported to the kidneys to form urine Learning Goal Describe the formation of urea from an ammonium ion Urea Cycle The urea cycle in the liver cells ID: 910953
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Slide1
24.7 Urea Cycle
The ammonium ion, the end product of amino acid degradation, is toxic if it is allowed to accumulate. The urea cycle converts ammonium ions to urea, which is transported to the kidneys to form urine.
Learning Goal Describe the formation of urea from an ammonium ion.
Slide2Urea Cycle
The urea cycle in the liver cells consists of reactions that occur in the mitochondria and cytosol.detoxifies ammonium ions from amino acid degradation.begins with the conversion of ammonium ions to carbamoyl phosphate using energy from two ATP.
Slide3Reaction 1: Transfer, Carbamoyl
GroupReaction 1 of the urea cycle occurs in the mitochondrial matrix, whereornithine transcarbamylase
catalyzes transfer of the carbamoyl group from carbamoyl phosphate to ornithine.the reaction yields citrulline, which is transported across the mitochondrial membrane by the citrulline transporter into the cytosol.hydrolysis of the high-energy phosphate bond in
carbamoyl
phosphate provides the energy to drive the reaction.
Slide4Reaction 1: Transfer, Carbamoyl
Group
Slide5Reaction 2: Condensation with Aspartate
Reaction 2 of the urea cycle occurs in the cytosol, whereargininosuccinate synthetase catalyzes the condensation of citrulline with aspartate, producing argininosuccinate.
the hydrolysis of two phosphate bonds in ATP to yield AMP and two inorganic phosphates provides energy for the reaction.
Slide6Reaction 3: Cleavage of Fumarate
Reaction 3 of the urea cycle occurs in the cytosol, whereargininosuccinate lyase splits
argininosuccinate.the products are arginine and fumarate, a citric acid cycle intermediate.
Slide7Reaction 4: Hydrolysis of Arginine
Reaction 4 of the urea cycle occurs in the cytosol, wherearginase catalyzes the hydrolysis of arginine. the products are urea and ornithine.
Ornithine returns to the mitochondrial matrix to repeat the urea cycle.
Slide8Urea Cycle, Overview
Slide9Study Check
Identify the site for each as either mitochondrion or cytosol.A. formation of ureaB. formation of carbamoyl
phosphateC. combination of aspartate with citrullineD. cleavage of fumarate
E. formation of
citrulline
Slide10Solution
Identify the site for each as either mitochondrion or cytosol.A. formation of urea
cytosolB. formation of carbamoyl phosphate mitochondrion
C. combination of aspartate with
citrulline
cytosol
D. cleavage of
fumarate
cytosol
E. formation of
citrulline
mitochondrion