LAWS OF THERMODYNAMICS First Law: E cannot be created or destroyed, only transformed. Second Law: When E is transformed, some cannot be used for work

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1 ENERGY, ENZYMES AND METABOLISM CHAPTER 8 Lecture Objectives What Physical Principles Underlie Biological Energy Transformations? What Is the Role of ATP in Biochemical Energetics? What Are Enzymes? How Do Enzymes Work? How Are Enzyme Activities Regulated? What is ENERGY? Capacity to do work Capacity for change Cellular energy? Transformations TYPES OF ENERGY POTENTIAL KINETIC METABOLISM ANABOLISM CATABOLISM LAWS OF THERMODYNAMICS First Law: E cannot be created or destroyed, only transformed Second Law: When E is transformed, some cannot be used for work In any system: ENTROPY ( disorder ) Total energy = usable energy + unusable energy

2 enthalpy (H) = free energy (G) + entropy (S) or H = G + TS (T = absolute temperature) G = H TS Change in energy can be measured in calories or joules. Change in free energy (ΔG) in a reaction is the difference in free energy of the products and the reactants. ΔG = ΔH TΔS If ΔG is negative, free energy is released If ΔG is positive, free energy is consumed If ΔG = 0 free energy is not available, the reaction does not occur. Magnitude of ΔG depends on: ΔH total energy added (ΔH > 0) or released (ΔH < 0) ΔS change in entropy. Large changes in entropy make ΔG more negative Second law of thermodynamics: Disorder tends to increase because of energy transformations. Living organisms must have a constant supply of energy to maintain order.

3 REACTIONS CAN BE Exergonic reactions release free energy ( ΔG): Catabolism; complexity decreases (generates disorder). OR Endergonic reactions consume free energy (+ΔG): anabolism; complexity (order) increases. EXERGONIC REACTION ENDERGONIC REACTION CHEMICAL EQUILIBRIUM At chemical equilibrium, ΔG = 0 Forward and reverse reactions are balanced. The concentrations of A and B determine which direction will be favored. A B CHECK FOR UNDERSTANDING! Which of the following best describes the two graphs below? a. The left graph shows an endergonic reaction with a + G. b. The left graph shows an exergonic reaction with a + G. c. The right graph shows an endergonic reaction with a + G. d. The right graph shows an exergonic reaction with a + G. Chemical rxns run to Equilibrium ADENOSINE TRIPHOSPHATE ATP

4 QUESTION! ADP COUPLING REACTIONS a. consists of adenine, ribose, and three phosphate groups. b. is produced in an endergonic reaction. c. can phosphorylate many different molecules. d. is poorer in energy than ATP. What are enzymes? Catalysts Not altered in reactions Most are proteins Lower energy needed for reaction to go forward ACTIVATION ENERGY SUBSTRATES/ENZYMES/PRODUCTS ENZYMES LOWER Ea ENZYMES CHANGE THEIR ORIENTATION ENZYMES STRETCH BONDS ENZYMES CAN ADD CHEMICAL GROUPS TO SUBSTRATES How Do Enzymes Work? Acid-base catalysis: Covalent catalysis: Metal ion catalysis:. INDUCED FIT

5 ONE MORE! Enzymes speed up chemical reactions by a. decreasing G. b. increasing activation energy. c. shifting the equilibrium toward products. d. forming an enzyme-substrate complex. Maximum Rate (Saturation) METABOLIC PATHWAYS Chemicals rxns interconnected with each other Systems Biology (Mathematical algorithms) Metabolic Pathway IRREVERSIBLE INHIBITION REVERSIBLE INHIBITION ALLOSTERIC REGULATION Allosteric regulation: An effector molecule binds to a regulatory subunit, inducing the enzyme to change its shape. Most allosteric enzymes are proteins with quaternary structure. Active site is on the catalytic subunit. Inhibitors and activators bind to the regulatory subunits. REMEMBER? An allosteric inhibitor binds to a. the enzyme s active site. b. the enzyme s substrate. c. the inactive form of the enzyme. d. the active form of the enzyme. ALLOSTERIC REGULATION ALLOSTERY AND RXN RATE

6 Feedback Inhibition in Metabolic Pathways How ph Affects Enzyme Activity Temperature and Enzyme Activity Isozymes: Enzymes that catalyze the same reaction but have different properties, such as optimal temperature. Organisms can use isozymes to adjust to temperature changes. Enzymes in humans have higher optimal temperature than enzymes in most bacteria a fever can denature the bacterial enzymes.