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6,7-423-08AACatabStudent - Lecture Amino Acid Catabolism I...

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Lecture: Amino Acid Catabolism I and II Objectives Understand the general pathway for the breakdown of all amino acids; where does each step occur in the human body? Know why glutamate, glutamine, and alanine are so important What are the five entry points into the CAC for carbon skeletons from amino acid degradation? What is meant by glucogenic and ketogenic amino acids? What is the glucose-alanine cycle and what is its significance in an active body? Why is a balanced diet essential to protein catabolism? What are the coenzymes important in protein catabolism? Be able to describe the steps between removal of nitrogen from the amino acid in a peripheral tissue until it is excreted in the urine Know the subcellular locations and names of the intermediates of the urea cycle. Know the reactants, products, cofactors and regulation of the regulated enzyme(s) of the urea cycle Know how the citric acid cycle and the CAC are integrated; where in the cell each occurs What is the point of the urea cycle? Why is it worth expenditure of ATP to make it work? Outline Amino Acid Catabolism I I. Proteins to amino acids We’ve been talking about carbos and lipids; today, the subject is amino acids. What do our bodies do with ingested and recycled protein? When a diet is rich in protein, protein is broken down to individual aas in stomach, small intestine by a variety of digestive enzymes. Free aas are transported across intestinal epithelium, carried in circulatory system When ingested amino acids exceed the body’s need for protein synthesis, the surplus is catabolized; The body cannot store excess aas the way it can store excess glucose and fats. Intracellular proteins are also broken down, if not needed at that moment, also contribute free aas. And, during starvation, heavy exercise, or in diabetes mellitus (i.e., when carbohydrates are either unavailable or not properly utilized) cellular proteins are extensively used as fuel. Amino groups resulting from the oxidative degradation of amino acids cannot be released as ammonia –it is highly toxic to our cells. The amino groups are either excreted or reused—in making new amino acids or in other nitrogen-containing molecules; N is hard
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to get, and precious. II. Amino acid degradation A. Splitting of carbon skeletons from amino groups Then what? The amino groups and the carbon skeletons take different routes (eventually interconnected). Well look at the carbon skeletons first. (Part I) Most amino acids are metabolized in the liver: lets look at this more closely 1. The general scheme for the further catabolism of these aas involves the transfer of amino groups to α -ketoglutarate (from CAC), forming glutamate plus an α -ketoacid. These reactions are catalyzed by aminotransferases, also called transaminases.
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6,7-423-08AACatabStudent - Lecture Amino Acid Catabolism I...

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