Lecture31-2007 - Major fates of glucose in cells:...

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1 Gluconeogenesis Lecture 31 Chapter 15, Section 4A, B Major fates of glucose in cells: Fatty Acids Gluconeogenesis • Net synthesis of glucose from non- carbohydrate precursors. • Why do cells do this? – Starvation conditions: • Normal adult needs ~160 g glucose/day (120 g/day for brain alone!) • Brain, RBC, retina use glucose as exclusive fuel. • Enough glucose in body to last 1-1.5 days: – Liver glycogen: ~190 g – Blood: ~20 g – Recovery of lactic acid from lactic acid fermentation. Non-carbohydrate precursors • Lactic acid • Amino acids, except for leucine and lysine. • Glycerol, from breakdown of triglycerides.
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2 Where does gluconeogenesis occur? • Major site: liver – Liver plays a major role in regulating blood glucose levels. • Minor site: kidney cortex • Other tissues: some gluconeogenesis, but cannot release glucose into blood. Gluconeogenesis not just a reversal of glycolysis • Recall glycolysis has three irreversible reactions: – Hexokinase – Phosphofructokinase – Pyruvate kinase • Gluconeogenesis provides three “bypass” reactions around these. • All other reactions (reversible reactions) are shared. Glycolysis Gluconeogenesis Bypass 1 Bypass 2 Bypass 3 Mitochondrial Matrix Movement across inner membrane requires antiporters (carriers) that maintain charge neutrality across membrane. Malate carrier Pi Pyruvate carrier OH - Malate dehydrogenase (cytoplasmic isozyme)
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3 Why move into the Mitochondrion? Malate carrier
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Lecture31-2007 - Major fates of glucose in cells:...

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