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Download Control of intra-cellular (enzyme regulator)
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CONTROL OF CARBOHYDRATE METABOLISM Control of metabolism can be simplified into: a) Control of intra-cellular (enzymes regulator) b) Systemic control (blood glucose) Control by enzymes activity An idealized cell in steady state. Note that metabolite flow is unidirectional. Despite the existence of short-term oscillations in metabolite concentrations and enzyme levels, living cells exist in a dynamic steady state in which the mean concentrations of metabolic intermediates remain relatively constant over time COMPARTMENTATION ENSURES METABOLIC EFFICIENCY & SIMPLIFIES REGULATION In eukaryotes, anabolic and catabolic pathways that interconvert common products may take place in specific sub cellular compartments. Enzymes that degrade proteins and polysaccharides reside inside organelles called lysosomes. Fatty acid biosynthesis occurs in the cytosol, whereas fatty acid oxidation takes place within mitochondria Segregation of certain metabolic pathways within specialized cell types can provide further physical compartmentation. Controlling an Enzyme That Catalyzes a Rate-Limiting Reaction Regulates an Entire Metabolic Pathway While the flux of metabolites through metabolic pathways involves catalysis by numerous enzymes, active control of homeostasis is achieved by regulation of only a select subset of these enzymes. The ideal enzyme for regulatory intervention is one whose quantity or catalytic efficiency dictates that the reaction it catalyzes is slow relative to all others in the pathway Quantity: synthesis degradation Synthesis in response to: metabolite hormone Degradation: damage to a prosthetic group covalent modifications allosteric effectors 2 ADP ATP + AMP Adenylyl kinase Utilization of ATP will increase amount of AMP Pyruvate Carboxylase : ↑ synthesis During fasting activated by FFA and Acetyl-CoA During fasting or starvation (DM): ↓activity of glycolysis, glycogenesis, HMP Shunt uronic acid path way ↑act. Glycogenolysis gluconeogenesis Carbohydrate metabolism Glucose turnover (basal state) 55% Oxidation 45% Brain 10% Muscle 75% Glycogenolysis Glucose 25% Gluconeogenesis 60% from lactate 20% Glycolysis (muscle) 25% Re-uptake (liver, gut) Blood glucose : ↑ gluconeogenesis, glycogenolysis, diet ↓ glycolysis, glycogenesis, HMP Shunt, uronic path way