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Unformatted text preview: Ch. 21 Regulation of Metabolism and Growth 1) Regulation of metabolic pathways since anabolic and catabolic pathways have several of the same intermediates, most important in determining which metabolic pathways are in operation is the number and activity of the enzymes involved 2) Energy Intake, Utilization, and Storage a Large molecules of food undergo three possible fates: i) Biomolecules can be broken down to smaller molecules, releading energy that can be used for driving cellular processes ii) They can be used to synthesize other molecules iii) Excess biomolecules are converted to energy storage molecules, generally glycogen or triglyceride b Carbs i) Molecules of glucose are transported into the cell by glucose transporters ii) Inside cells it is oxidized for energy, which generates CO 2 as a waste product and provides substrates for other reactions, or is converted to glycogen for storage c Proteins i) Amino acids, not whole proteins ,are transported in the bloodstream ii) Following uptake in cells, they are used for the synthesis of proteins or catabolized for energy by proteolysis iii) Catabolism of cellular proteins occurs only during periods of starvation, and it generates ammonia, which is converted to urea in the LIVER d Fats i) Triglycerides transported in the bloodstream in lipoproteins, but they must leave them before they enter the cell ii) To facilitate entry, triglycerides at the outer surface of the lipoporoteins are broken down by the enzyme lipoprotein lipase, which is located on the inside surface of capillaries throughout the body; this enzyme breaks down the tris into fatty acids and monoglycerides; the fatty acids are taken up by cells iii) Monoglycerides remain in the bloodstream are eventually metabolized in the liver iv) Upon entering cells, the fatty acids may be oxidized for energy, used to make new triglycerides (stored in fat droplets in cytosol, mainly in adipocytes) v) Stored triglycerides can be broken down to glycerol and fatty acids for energy in lipolysis 3) Energy Balance a Energy Output i) In a calorimeter, all the energy contained in a molecule is converted to heat during oxidation ii) The energy released during oxidation or other catabolic reactions takes two forms: heat and work; 60% goes to heat production and 40% goes to synthesize ATP for cellular work b BMR rate of energy expenditure of a person who is awake, lying down, relaxed, and has fasted 12 hours c Negative and Positive Energy Balance i) Positive Energy balance = more intake than output, weight gain 4) Energy Metabolism During the Absorptive and Postabsorptive States...
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- Spring '07