NUTR 470 1st Edition Lecture 22 Ammonia— is an important source of nitrogen for living systems.Glucose-alanine cycle— is used primarily as a mechanism for skeletal muscle to eliminate nitrogen.Urea— is the major end product of nitrogen catabolism.In the liver:Conversion of _____ to ______ produces free ammonia, which is then converted to urea through urea cycle.glutamineglutamate1st ReactionHydrolysis by: glutaminaseA reaction of the Urea Cycle:Formation of carbamoyl phosphateMitochondrial reactionEnzyme: Carbamoyl phosphate synthase I (CPS-I)2nd ReactionA reaction of the Urea Cycle:Formation of citrullineMitochondrial reactionL-Ornithine transcarboamoylase catalyzes transfer of the carbamoyl group of carboamoyl phosphate to ornithine, forming citrulline.Carbamoyl phosphate synthase I (CPS-I) initiates urea biosynthesis.3rd ReactionReaction of Urea Cycle:Formation of argininosuccinateCytosolic reactionArgininosuccinate synthase links aspartate and citrulline via the amino group of aspartate and provides the second nitrogen of urea.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.4th ReactionReaction of Urea Cycle:Cleavage of argininosuccinateCytosolic reactionArgininosuccinase catalyzes the cleavage of argininosuccinate, forming arginine and fumarate.5th ReactionReaction of Urea Cycle:Cleavage of arginineCytosolic reactionArginase catalyzes the hydrolytic cleavage of the guanidino group of arginine, releasing urea.The urea cycle operates only to eliminate excess nitrogenWhen dietary proteins increase significantly, levels of enzymes involved in the urea cyclerise
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