Integration of Energy Metabolism

Integration of Energy Metabolism - C H A P T E R 17...

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190 C H A P T E R 17 INTEGRATION OF ENERGY METABOLISM Integrating Metabolic Pathways Adipose ATP Brain Glucose Connection of Storage Pools Storage Molecules Feeding Metabolic States and Signals Fasting Insulin Starvation Glucagon Excitement Epinephrine Interorgan Cycles Secondary Signals Cori Cycle Generalities of Metabolism Alanine Cycle Phosphorylation Ketone Bodies Glycogen Metabolic Movements of Glycogen Fat Metabolic Movements of Fat Protein Metabolic Movements of Protein Tissue Cooperation Liver Muscle
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17 Integration of Energy Metabolism 191 Welcome to energy metabolism. It’s the nuts and bolts of life at the cel- lular level. 1 Energy metabolism is responsible for maintaining a constant supply of ATP in all different tissues. Since some tissues, such as red cells and brain, rely heavily on glucose to make ATP, maintaining the ATP levels in all tissues requires maintaining the availability of glucose. The purpose of all the pathways we’ll discuss is to maintain ATP and glucose supplies. As you prowl around the individual metabolic pathways of energy metabolism, you need to get a feel for the kinds of things you should be looking for as you examine each metabolic scheme. There are four indi- vidual pathways involved in energy metabolism: glycolysis-gluconeoge- nesis, fatty acid synthesis– b oxidation, glycogen synthesis-degradation, and the TCA cycle. First look for the overall function of each pathway: What does it do? This involves knowing the molecules coming into the pathway and those going out. Next, understand when the pathway should be on or off—what metabolic states require the pathway to function. Then, figure out which tissues use the pathway and how. Finally, see how the behavior of the pathway may be integrated into the cooperation between organs and tissues. Energy metabolism makes sense if you realize that each individual pathway and each organ has a function. Understanding metabolism in every detail may well be impossible, but understanding the general themes is not only possible but important. Energy metabolism maintains the supply of ATP and glucose by making storage molecules ( glycogen , fat , protein ) when food is available and by retrieving ATP and glucose from storage when they are needed. The need for glucose or ATP may constitute a demand for massive amounts of immediate energy or it may simply be the need to maintain energy and glucose levels between meals. Energy metabolism is regu- lated in a manner that involves extensive cooperation between different organs, but the goal is always the same: to maintain adequate ATP and glucose levels. Most of energy metabolism should make sense—don’t forget that. The function of energy metabolism is reasonably simple—
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This note was uploaded on 04/09/2008 for the course BIO SCI 98 taught by Professor Goulding during the Spring '08 term at UC Irvine.

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Integration of Energy Metabolism - C H A P T E R 17...

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