TAILIEUCHUNG - Biochemistry, 4th Edition P73

Biochemistry, 4th Edition P73. Continuing Garrett and Grisham's innovative conceptual and organizing framework, "Essential Questions," BIOCHEMISTRY guides students through course concepts in a way that reveals the beauty and usefulness of biochemistry in the everyday world. Streamlined for increased clarity and readability, this edition also includes new photos and illustrations that show the subject matter consistently throughout the text. New end-of-chapter problems, MCAT practice questions, and the unparalleled text/media integration with the power of CengageNOW round out this exceptional package, giving you the tools you need to both master course concepts and develop critical problem-solving skills you can draw upon. | Can Glucose Provide Electrons for Biosynthesis 683 turn activate some 800 molecules of phosphorylase. Each of these catalyzes the formation of many molecules of glucose-1-P. The Difference Between Epinephrine and Glucagon Although both epinephrine and glucagon exert glycogenolytic effects they do so for quite different reasons. Epinephrine is secreted as a response to anger or fear and may be viewed as an alarm or danger signal for the organism. Called the fight or flight hormone it prepares the organism for mobilization of large amounts of energy. Among the many physiological changes elicited by epinephrine one is the initiation of the enzyme cascade as in Figure which leads to rapid breakdown of glycogen inhibition of glycogen synthesis stimulation of glycolysis and production of energy. The burst of energy produced is the result of a 2000-fold amplification of the rate of glycolysis. Because a fear or anger response must include generation of energy in the form of glucose both immediately in localized sites the muscles and eventually throughout the organism as supplied by the liver epinephrine must be able to activate glycogenolysis in both liver and muscles. Glucagon is involved in the long-term maintenance of steady-state levels of glucose in the blood. It performs this function by stimulating the liver to release glucose from glycogen stores into the bloodstream. To further elevate glucose levels glucagon also stimulates liver gluconeogenesis by activating F-2 6-BPase activity see Figure . It is important to note however that stabilization of blood glucose levels is managed almost entirely by the liver. Glucagon does not activate the phosphorylase cascade in muscle muscle membranes do not contain glucagon receptors . Muscle glycogen breakdown occurs only in response to epinephrine release and muscle tissue does not participate in maintenance of steady-state glucose levels in the blood. Glucagon and epinephrine both trigger glycogen breakdown

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• RNA trao đổi chất
• nguyên tắc của hóa sinh
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