Biochemistry, 4th Edition P43. 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. | What Characteristic Features Define Enzymes 383 Enzymes Are the Agents of Metabolic Function Acting in sequence enzymes form metabolic pathways by which nutrient molecules are degraded energy is released and converted into metabolically useful forms and precursors are generated and transformed to create the literally thousands of distinctive biomolecules found in any living cell Figure . Situated at key junctions of metabolic pathways are specialized regulatory enzymes capable of sensing the momentary metabolic needs of the cell and adjusting their catalytic rates accordingly. The responses of these enzymes ensure the harmonious integration of the diverse and often divergent metabolic activities of cells so that the living state is promoted and preserved. What Characteristic Features Define Enzymes Enzymes are remarkably versatile biochemical catalysts that have in common three distinctive features catalytic power specificity and regulation. Catalytic Power Is Defined as the Ratio of the Enzyme-Catalyzed Rate of a Reaction to the Uncatalyzed Rate Enzymes display enormous catalytic power accelerating reaction rates as much as 1021 over uncatalyzed levels which is far greater than any synthetic catalysts can achieve and enzymes accomplish these astounding feats in dilute aqueous solutions under mild conditions of temperature and pH. For example the enzyme jack bean urease catalyzes the hydrolysis of urea O H . . H2N C NH2 2 H2O H ---------n 2 NH4 1 IC 3 At 20 C the rate constant for the enzyme-catalyzed reaction is 3 X 104 sec the rate constant for the uncatalyzed hydrolysis of urea is 3 X 10-10 sec. Thus 1014 is the ratio of the catalyzed rate to the uncatalyzed rate of reaction. Such a ratio is defined as the relative catalytic power of an enzyme so the catalytic power of urease is 1014. Glucose Hexokinase Glucose-6-P Phosphoglucoisomerase Fructose-6-P Phosphofructokinase Fructose-1 6-bis P Aldolase Glyceraldehyde-3-P Dihydroxyace tone-P Triose-P .
