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Lecture 17

HTHSCI 1LL3 Lecture 17: Urea cycle

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Health Sciences
Peter Helli

The Urea Cycle and Reactive Oxygen Species Tuesday, March 21, 2017 Amino Acid Metabolism Protein is the only N containing micronutrient Cant store protein as protein Have to take N off and turn it into glucose or fat so it can be stored as adipose tissue Use the carbon skeleton Ammonium ion is predominant species Urea Formation Liver is the main site where enzymes are available to participate in urea cycle Generate ammonia in other places Take amino group off from one carbon skeleton, put it on another, have another amino acid Prolonged fasting = protein from muscle that can be turned into glucose Vitamin B6 is heavily involved, enzyme wont work without it The GlucoseAlanine Cycle Muscle using glucose in glycolysis and generating pyruvate and a couple of ATP, where it can be converted to alanine and travel back to liver Gets rid of some nitrogen Sent back to liver, cycle through, and then goes back to muscle as glucose Cycle constantly going on to maintain blood glucose and muscles have sufficient energy supplies Nitrogen Excretion Elevated levels of ammonia = problem with liver Take in nitrogen in the form of protein and excrete mostly as urea, equal amounts High levels of ammonia is toxic and dangerous to nervous system High levels of ammonia = problem with liver Healthy liver can turn all the nitrogen into urea Elevated levels of blood urea nitrogen = problem with kidney Steps in the Urea Cycle Deficient in any one of the enzymes, have a problem converting ammonia to urea Different treatments for each one Arginase arginine : easiest one to fix Reactive Oxygen Species (ROS) Tissues require oxygen in order for mitochondria to work If we have oxygens that are missing an electron, we have free radicals or ROS Very reactive compounds that will grab an electron from somewhere else and cause damage Superoxide radicals (o2) and hydroxyl radical (OH with a dot) Sources of ROS Free radicals are intermediate compounds locked in enzyme, but if they escape they are problematic Exposure to ionizing radiation
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