Energy and Metabolism

1. Energy and Metabolism Chapter 4 Part 1

2. 4.1 Impacts/IssuesA Toast to Alcohol Dehydrogenase • Metabolic processes break down organic molecules such as ethanol and other toxins – binge drinking is currently the most serious drug problem on college campuses

3. Video: Alcohol, enzymes, and your liver

4. Alcohol dehydrogenase (ADH) converts ethanol to toxic acetaldehyde, which is then converted to acetate by ALDH

5. 4.2 Life Runs on Energy Laws of Thermodynamics • Energy • The capacity to do work Law #1 Energy can be converted from one form to another, but cannot be created or destroyed – Law #2 Energy disperses spontaneously

6. Material Recycle • Energy inputs drive a cycling of materials among producers and consumers • Producers and then consumers use energy to assemble, rearrange, and break down organic molecules that cycle among organisms throughout ecosystems

7. ENERGY IN Light energy radiating from the sun reaches Earth. Producers capture some of it by converting it to chemical energy. They and all other organisms use chemical energy to drive cellular work. PRODUCERS One way Flow of energy plants and other self-feeding organisms nutrient cycling CONSUMERS animals, most fungi, many protists, bacteria ENERGY OUT With each conversion, there is a one- way flow of a bit of energy back to the environment, mainly in the form of heat. Fig. 4-2, p. 63

8. Matter recycling and energy flow

9. 4.3 Energy in the Molecules of Life • Cells store and retrieve energy by making and breaking chemical bonds in metabolic reactions • Some reactions require a net input of energy – others end with a net release of energy

10. Chemical Reactions • Reaction • Process of chemical change • Reactant • Molecule that enters a reaction • Product • A molecule remaining at the end of a reaction

11. A Chemical Reaction

12. Energy Inputs and Outputsin Chemical Reactions • Chemical bonds hold energy – the amount depends on which elements take part in the bond • Cells store energy in chemical bonds by running energy-requiring reactions, and access energy by running energy-releasing reactions

13. Energy Inputs and Outputsin Chemical Reactions

14. Why the World Doesn’t Go Up in Flames • Molecules of life release energy when combined with oxygen – but not spontaneously – energy is required to start even energy-releasing reactions • Activation energy • Minimum amount of energy required to start a reaction

15. Reactants: 2 H2 + O2 Activation energy Difference in energy between reactants and products Products: 2 H2O Activation Energy Energy Time Stepped Art Fig. 4-4, p. 65

16. Animation: Chemical equilibrium

17. ATP – The Cell’s Energy Currency • Energy carriers accept energy from energy-releasing reactions and deliver energy to energy-requiring reactions • ATP (Adenosine triphosphate) • Main energy carrier between reaction sites in cells

18. Phosphorylation • Phosphate-group transfers (phosphorylation) to and from ATP couple energy-releasing reactions with energy-requiring ones

19. ATP: The Energy Currency of Cells

20. 4.4 How Enzymes Work • Enzymes make chemical reactions proceed much faster than they would on their own • Enzyme • Protein or RNA that speeds a reaction without being changed by it

21. Substrates • An enzyme’s particular substrates bind at its active site • Substrate • A reactant molecule that is specifically acted upon by an enzyme

22. Active Sites • Active site • Pocket in an enzyme where substrates bind and a reaction occurs

23. Factors That Influence Enzyme Activity • Each enzyme works best within a characteristic range of temperature, pH, and salt concentration • When conditions break hydrogen bonds, an enzyme changes its characteristic shape (denatures), and stops working

24. Enzymes, Temperature, and pH

25. Fig. 4-6a, p. 66

26. Organized, Enzyme-Mediated Reactions • Cells concentrate, convert, and dispose of most substances in enzyme-mediated reaction sequences • Metabolic pathway • Series of enzyme-mediated reactions by which cells build, remodel, or break down an organic molecule

27. Linear and Cyclic Metabolic Pathways

28. Control of Metabolic Pathways • Various controls over enzymes allow cells to conserve energy and resources by producing only what they require • Concentrations of reactants and products • Feedback inhibition

29. Control of Metabolic Pathways • Feedback inhibition • Mechanism by which a change that results from some activity decreases or stops the activity

30. Feedback Inhibition

31. Electron Transfers • Electron transfer chains allow cells to harvest energy in manageable increments • Electron transfer chain • An array of membrane-bound enzymes and other molecules that accept and give up electrons in sequence

32. Uncontrolled and Controlled Energy Release 1 Energy input splits glucose into carbon dioxide, electrons, and hydrogen ions (H+). carbon dioxide glucose carbon dioxide glucose e– + 2 Electrons lose energy as they move through an electron transfer chain. + oxygen water oxygen H+ spark 3 Energy released by electrons is harnessed for cellular work. e– 4 Electrons, hydrogen ions, and oxygen combine to form water. water B The same overall reaction occurs in small steps with an electron transfer chain. Energy is released in amounts that cells can harness for cellular work. A Glucose and oxygen react (burn) when exposed to a spark. Energy is released all at once as light and heat when CO2 and water form. Stepped Art Fig. 4-9, p. 68