1. Ground 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 2H 2 O 2 ----------> 2H 2 O + O 2

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 All organisms 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 energy than starting substances product with more energy (plus by-products 60 2 and 6H 2 O) ENERGY IN 612

14. Exergonic Reactions Energy is released Products have less energy than starting substance ENERGY OUT energy-rich starting substance + 60 2 products with less energy 66

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

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. 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

19. 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)

20. 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

21. 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

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

23. Chemical Equilibrium At equilibrium, the energy in the reactants equals that in the products Product and reactant molecules usually differ in energy content Therefore, at equilibrium, the amount of reactant almost never equals the amount of product

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

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

26. Types of Reaction Sequences BRANCHING PATHWAY: LINEAR PATHWAY:CYCLIC PATHWAY: ABCDE F KJI G NML H

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

28. 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

29. 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

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

31. Induced-Fit Model two substrate molecules active sight substrates contacting active site of enzyme TRANSITION STATE (tightest binding but least stable) end product enzyme unchanged by the reaction 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

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

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

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

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

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

37. Effect of pH

38. 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

39. Cell Membranes Show Selective Permeability O 2, CO 2, and other small nonpolar molecules;and H 2 O C 6 H 12 O 6, and other large, polar (water-soluble) molecules; ions such as H +, Na +, CI -, Ca ++ ; plus H 2 O hydrogen-bonded to them X

40. Membrane Crossing Mechanisms Diffusion across lipid bilayer Passive transport Active transport Endocytosis Exocytosis

41. Span the lipid bilayer Interior is able to open to both sides Change shape when they interact with solute Play roles in active and passive transport Transport Proteins

42. Passive Transport Flow of solutes through the interior of passive transport proteins down their concentration gradients Passive transport proteins allow solutes to move both ways Does not require any energy input

43. Passive Transport solute

44. Active Transport Net diffusion of solute is against concentration gradient Transport protein must be activated ATP gives up phosphate to activate protein Binding of ATP changes protein shape and affinity for solute

45. Active Transport ATP gives up phosphate to activate protein Binding of ATP changes protein shape and affinity for solute P P P P High solute concentration Low solute concentration ATP ADP

46. Bulk Transport Exocytosis Endocytosis

47. Osmosis Diffusion of water molecules across a selectively permeable membrane Direction of net flow is determined by water concentration gradient Side with the most solute molecules has the lowest water concentration

48. Tonicity Refers to relative solute concentration of two fluids Hypertonic - having more solutes Isotonic - having same amount Hypotonic - having fewer solutes

49. Tonicity and Osmosis 2% sucrose water10% sucrose 2% sucrose

50. Increase in Fluid Volume compartment 1 HYPOTONIC SOLUTION membrane permeable to water but not to solutes HYPERTONIC SOLUTION compartment 2 fluid volume increases In compartment 2

51. Pressure and Osmosis Hydrostatic pressure –Pressure exerted by fluid on the walls that contain it –The greater the solute concentration of the fluid, the greater the hydrostatic pressure Osmotic pressure –Amount of pressure necessary to prevent further increase of a solution’s volume