Energy and Life Ground Rules of Metabolism

1. Energy and LifeGround Rules of Metabolism Chapter 5

2. Growing Old with Molecular Mayhem Free radical A molecule that has unpaired electrons Highly reactive, can disrupt structure of molecules

3. Superoxide Dismutase • Catalyzes the formation of hydrogen peroxide from oxygen free radicals and hydrogen ions • Accumulation of hydrogen peroxide can be lethal to cells

4. Catalase Catalyzes the formation of oxygen and water from hydrogen peroxide 2H2O2 ----------> 2H2O + O2

5. Roundworm Experiments • Diet supplemented with superoxide dismutase and catalase increased life span of normal worms • Diet also allowed worms genetically-engineered for susceptibility to free radicals to live normal life span

6. What is Energy? • Capacity to do work • Forms of energy • Potential energy • Kinetic energy • Chemical energy

7. What Can Cells Do with Energy? • Energy inputs become coupled to energy-requiring processes • Cells use energy for: • Chemical work • Mechanical work • Electrochemical work

8. First Law of Thermodynamics • The total amount of energy in the universe remains constant • Energy can undergo conversions from one form to another, but it cannot be created or destroyed

9. One-Way Flow of Energy • The sun is life’s primary energy source • Producers trap energy from the sun and convert it into chemical bond energy • Allorganisms use the energy stored in the bonds of organic compounds to do work

10. Second Law of Thermodynamics • No energy conversion is ever 100 percent efficient • The total amount of energy is flowing from high-energy forms to forms lower in energy

11. Entropy • Measure of degree of disorder in a system • The world of life can resist the flow toward maximum entropy only because it is resupplied with energy from the sun

12. Energy Changes & Cellular Work Energy changes in cells tend to run spontaneously in the direction that results in a decrease in usable energy

13. Endergonic Reactions • Energy input required • Product has more stored or potential energy than starting substances product with more energy (plus by-products 602 and 6H2O) ENERGY IN 6 12

14. Exergonic Reactions • Energy is released • Products have less energy than starting substance energy-rich starting substance ENERGY OUT + 602 6 6 products with less energy

15. The Role of ATP • Cells “earn” ATP in exergonic reactions • Cells “spend” ATP in endergonic reactions adenine P P P ribose

16. Electron Transfers • Electrons are transferred in virtually every reaction that harnesses energy for use in the formation of ATP • Coenzymes assist in electron transfers

17. Electron Transport Systems • Arrangement of enzymes, coenzymes, at cell membrane • As one molecule is oxidized, next is reduced • Function in aerobic respiration and photosynthesis

18. Oxidation and Reduction • Oxidation is the loss of electrons by an atom or molecule • Reduction is the gain of electrons by an atom or molecule. • Oxidation of molecule A is always accompanied by reduction of a molecule B or vice-versa. (An e- donor requires an e- acceptor or vice-versa)

19. Concentration Gradient • Means the number of molecules or ions in one region is different than the number in another region • In the absence of other forces, a substance moves from a region where it is more concentrated to one one where it’s less concentrated - “down” gradient

20. Diffusion • The net movement of like molecules or ions down a concentration gradient • Although molecules collide randomly, the net movement is away from the place with the most collisions (down gradient)

21. Factors Affecting Diffusion Rate • Steepness of concentration gradient • Steeper gradient, faster diffusion • Molecular size • Smaller molecules, faster diffusion • Temperature • Higher temperature, faster diffusion • Electrical or pressure gradients

22. Which Way Will a Reaction Run? • Nearly all chemical reactions are reversible • Direction reaction runs depends upon • Energy content of participants • Reactant-to-product ratio

23. Chemical Equilibrium RELATIVE CONCENTRATION OF REACTANT RELATIVE CONCENTRATION OF PRODUCT HIGHLY SPONTANEOUS EQUILIBRIUM HIGHLY SPONTANEOUS

24. Chemical Equilibrium • At equilibrium, the energy in the reactants equals that in the products • Product and reactant molecules usually differ in potential energy content (E > e) • Therefore, at equilibrium, the amount (n) of reactant almost never equals the amount (N) of product (n*E= N*e ; where N>n and E>e)

25. Energy Relationships large energy-rich molecules (fats, complex carbohydrates, proteins, nucleic acids) ADP + Pi BIOSYNTHETIC PATHWAYS (ANABOLIC) DEGRADATIVE PATHWAYS (CATABOLIC) simple organic compounds (simple sugars, amino acids, fatty acids, nucleotides) ATP energy-poor products (such as carbon dioxide, water) ENERGY INPUT

26. Energy Carriers Enzymes Cofactors Participants in Metabolic Pathways • Substrates • Intermediates • End products

27. Types of Reaction Sequences LINEARPATHWAY: CYCLICPATHWAY: A B C D E F G K J I N M L H BRANCHINGPATHWAY:

28. Enzyme Structure and Function Enzymes are catalytic molecules They speed the rate at which reactions approach equilibrium

29. Four Features of Enzymes 1) Enzymes do not make anything happen that could not happen on its own. They just make it happen much faster 2) Reactions do not alter or use up enzyme molecules

30. Four Features of Enzymes 3) The same enzyme usually works for both the forward and reverse reactions 4) Each type of enzyme recognizes and binds to only certain substrates

31. Activation Energy • For a reaction to occur, an energy barrier must be surmounted • Enzymes make the energy barrier smaller activation energy without enzyme starting substance activation energy with enzyme energy released by the reaction products

32. two substrate molecules Induced-Fit Model substrates contacting active site of enzyme • Substrate molecules are brought together • Substrates are oriented in ways that favor reaction • Active sites may promote acid-base reactions • Active sites may shut out water active sight TRANSITION STATE (tightest binding but least stable) end product enzyme unchanged by the reaction

33. Factors Influencing Enzyme Activity Temperature pH Salt concentration Allosteric regulators Coenzymes and cofactors

34. Allosteric Activation enzyme active site allosteric activator vacant allosteric binding site active site cannot bind substrate active site altered, can bind substrate

35. Allosteric Inhibition allosteric inhibitor allosteric binding site vacant; active site can bind substrate active site altered, can’t bind substrate

36. Feedback Inhibition enzyme 2 enzyme 3 enzyme 4 enzyme 5 A cellular change, caused by a specific activity, shuts down the activity that brought it about enzyme 1 END PRODUCT (tryptophan) SUBSTRATE

37. Effect of Temperature • Small increase in temperature increases molecular collisions, reaction rates • High temperatures disrupt bonds and destroy the shape of active site

38. Effect of pH

39. Enzyme Helpers • Cofactors • Coenzymes • NAD+, NADP+, FAD • Accept electrons and hydrogen ions; transfer them within cell • Derived from vitamins • Metal ions • Ferrous iron in cytochromes