An Introduction to Metabolism Chapter 8 An Introduction to Metabolism Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Living Organisms and Order How do living organisms create macromolecules, organelles, cells, tissues, and complex higher-order structures? The laws of thermodynamics do not apply to living organisms. Living organisms create order by using energy from the sun. Living organisms create order locally, but the energy transformations generate waste heat that increases the entropy of the universe. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Free Energy, Enthalpy, and Entropy When sodium chloride (table salt) crystals dissolve in water, the temperature of the solution decreases. This means that, for dissociation of Na+ and Cl– ions, the change in enthalpy (ΔH) is negative. the change in enthalpy (ΔH) is positive, but the change in entropy is greater. the reaction is endergonic, because it absorbs heat. the reaction must be coupled to an exergonic reaction. the reaction cannot occur spontaneously. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Life and Chemical Equilibrium Are chemical reactions at equilibrium in living cells? yes no only the exergonic reactions all reactions except those powered by ATP hydrolysis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Free Energy A reaction has a ∆G of -5. 6 kcal/mol Free Energy A reaction has a ∆G of -5.6 kcal/mol. Which of the following would most likely be true? The reaction could be coupled to power an endergonic reaction with a ∆G of +8.8 kcal/mol. The reaction would result in a decrease in entropy (S) and an increase in the energy content (H) of the system. The reaction would result in an increase in entropy (S) and a decrease in the energy content (H) of the system. The reaction would result in products with a greater free-energy content than in the initial reactants. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Rate of a Chemical Reaction The oxidation of glucose to CO2 and H2O is highly exergonic: ΔG = –636 kcal/mole. Why doesn’t glucose spontaneously combust? The glucose molecules lack the activation energy at room temperature. There is too much CO2 in the air. CO2 has higher energy than glucose. The formation of six CO2 molecules from one glucose molecule decreases entropy. The water molecules quench the reaction. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Enzymes Firefly luciferase catalyzes the reaction luciferin + ATP ↔ adenyl-luciferin + pyrophosphate then the next reaction occurs spontaneously: adenyl-luciferin + O2 → oxyluciferin + H2O + CO2 + AMP + light What is the role of luciferase? Luciferase makes the ΔG of the reaction more negative. Luciferase lowers the transition energy of the reaction. Luciferase alters the equilibrium point of the reaction. Luciferase makes the reaction irreversible. all of the above Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Enzyme-Catalyzed Reactions In the energy diagram below, which of the lettered energy changes would be the same in both the enzyme-catalyzed and uncatalyzed reactions? A B C D E Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Enzyme Inhibitors Vioxx and other prescription non-steroidal anti-inflammatory drugs (NSAIDs) are potent inhibitors of the cycloxygenase-2 (COX-2) enzyme. High substrate concentrations reduce the efficacy of inhibition by these drugs. These drugs are competitive inhibitors. noncompetitive inhibitors. allosteric regulators. prosthetic groups. feedback inhibitors. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Enzyme Regulation Adenosine monophosphate (AMP) activates the enzyme phosphofructokinase (PFK) by binding at a site distinct from the substrate binding site. This is an example of cooperative activation. allosteric activation. activation by an enzyme cofactor. coupling exergonic and endergonic reactions. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.