2. The Working Cell: Energy and Enzymes CHAPTER 5 Energy Concepts Conservation of Energy Entropy and Work Chemical Energy and Conversion ATP and Cellular Work ATP Structure Phosphate Transfer and Cycle Enzymes The Powering of Chemical Reactions Activation Energy Loss of Enzyme Function Temperature and pH Inhibitors

3. Energy is defined as the capacity to perform work. Kinetic energy is the energy of motion Potential energy is stored energy Potential energy can be converted into kinetic energy, and vice versa (but some energy is lost in conversion) Energy can neither be created nor destroyed Energy Concepts

4. Energy Lost in Conversion Energy lost during conversions is usually heat energy –Heat is type of kinetic energy. The term entropy as a measure of disorder, or randomness. –All energy conversions increase the entropy (disorder) of the universe. Chemical potential energy (food, gasoline, propane) is used by machines and living things to do work. –Not all the chemical energy is converted to work

5. Energy Conversions: Car and Cell

6. Cellular respiration in living things –The energy-releasing chemical breakdown of food/fuel molecules. –Food chemical energy is converted into usable cellular energy Food is a Type of Chemical Energy Used By Our Bodies Food + Oxygen gas  Carbon dioxide + Water + Usable Cellular Energy Food + O 2  CO 2 + H 2 O + ATP (like glucose sugar) (adenosine triphosphate)

7. The Working Cell: Energy and Enzymes CHAPTER 5 Energy Concepts Conservation of Energy Entropy and Work Chemical Energy and Conversion ATP and Cellular Work ATP Structure Phosphate Transfer and Cycle Enzymes The Powering of Chemical Reactions Activation Energy Loss of Enzyme Function Temperature and pH Inhibitors

8. Usable Cellular Energy (ATP) ATP (adenosine triphosphate) –The basic energy carrier is ADP (adenosine diphosphate) –Energy is stored in ADP by adding a third phosphate using a high-energy bond –The chemical energy from food powers the linkage of ADP to a third phosphate to become ATP

9. The Energy Stored in ATP Can Be Used to Perform Work in the Cell The energy released by ATP breaking down into ADP and P can power a variety of needs in the cell ADP P P Energized ATP: Discharged ATP: X Y+ Z Powering the synthesis of molecule Z:

10. The Working Cell: Energy and Enzymes CHAPTER 5 Energy Concepts Conservation of Energy Entropy and Work Chemical Energy and Conversion ATP and Cellular Work ATP Structure Phosphate Transfer and Cycle Enzymes The Powering of Chemical Reactions Activation Energy Loss of Enzyme Function Temperature and pH Inhibitors

11. Chemical Reactions within a Cell Metabolism is the word that describes all the chemical reactions within a cell Catabolism (catabolic reactions) are breakdown reactions that liberate energy Anabolism (anabolic reactions) are buildup reactions that absorb energy

12. Cellular Reactions Either Use or Liberate Energy Catabolic/Breakdown Reactions release energy oMolecules become more disorganized or less structured Anabolic/Buildup Reactions absorb energy oMolecules become more ordered and complex oATP needed to power endothermic reactions Z X Y + + C A B + + ATP

13. Cellular Reactions Either Use or Liberate Energy Breakdown Reactions Release Energy Buildup Reactions Absorb or Require Energy Z X Y + + C A B ++ ATP Energy Level Time Z X + Y A+ B C Activation Energy Activation Energy

14. Activation Energy Activation energy –Energy needed to allow the reactants to form products –Necessary for a chemical reaction to proceed –Activation energy is needed even for breakdown reaction to get them going Energy Level Time Z X + Y Activation Energy In the laboratory, we heat the reactants in order to provide activation energy for a chemical reaction Inside the cell, a different mechanism is required as heating up the reactants is not possible Lower the energy required for the reaction

15. Figure 5.8 Enzymes Lower Activation Energy and Speed Up Reactions

16. Enzymes Catalyze Chemical Reactions in Living Things Biomolecules call enzymes lower activation energy –Enzymes are folded proteins –Enzymes act as coordinators in a chemical reaction, thereby speeding them up –Enzymes are catalysts for reactions; they speed them up

17. Other Aspects of Enzymes Each enzyme is very selective –It has a pocket called the active site where reactants (substrates) bind for catalysis –Only substrates with certain shapes can bind to the enzyme and be catalyzed –Any particular enzyme therefore catalyzes only a specific reaction with specific substrates

18. glucose-fructose How Enzyme Catalyzes the Breakdown of Sucrose Sugar Energy Level Time sucrose glucose + fructose Energy Level Cannot progress because activation energy too formidable Energy Level glucose + fructose Time How Enzymes Work

19. The Working Cell: Energy and Enzymes CHAPTER 5 Energy Concepts Conservation of Energy Entropy and Work Chemical Energy and Conversion ATP and Cellular Work ATP Structure Phosphate Transfer and Cycle Enzymes The Powering of Chemical Reactions Activation Energy Loss of Enzyme Function Temperature and pH Inhibitors

20. Limitations of Enzyme Catalyzed Reactions Three-dimensional structure of an enzyme is key to its functionality –Anything which disrupts the intricate 3-D structure of the active site ruins its ability to catalyze a reaction –Substrates cannot bind to a distorted active site Environmental changes that will ruin enzyme activity by causing denaturation (unfolding) –Very high or very low pH –Very high temperatures (low temps just slow things down) –The presence of inhibitory molecules

21. Enzymes Become Non-Functional at pH Extremes and High Temperatures 0 2 4 6 8 10 12 Enzymatic rate (products formed per second) pH (in pH units) 10 20 30 40 50 60 70 Enzymatic rate (products formed per second) Temperature ( o C) Stomach enzyme OH - H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Enzyme within a body cell = folded, functional enzyme = denatured, non-functional enzyme Reaction rate is slow at cold temperatures because molecules encounter enzyme less often Enzyme from hot springs bacterium Enzyme within a body cell

22. Inhibitors That Mimic the Normal Substrate A competitive inhibitor

23. Inhibitors That Bind to Other Enzyme Pockets A non-competitive inhibitor

24. The Working Cell: Energy and Enzymes CHAPTER 5 Energy Concepts Conservation of Energy Entropy and Work Chemical Energy and Conversion ATP and Cellular Work ATP Structure Phosphate Transfer and Cycle Enzymes The Powering of Chemical Reactions Activation Energy Loss of Enzyme Function Temperature and pH Inhibitors