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Chapter 6

Chapter 6. Ground Rules of Metabolism. Impacts, Issues: Alcohol, Enzymes, and Your Liver. Catalase is an enzyme that helps the body break down toxic substances in alcoholic drinks. Impacts, Issues: Alcohol, Enzymes, and Your Liver. The liver plays a central role in alcohol metabolism

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Chapter 6

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  1. Chapter 6 Ground Rules of Metabolism

  2. Impacts, Issues: Alcohol, Enzymes, and Your Liver • Catalase is an enzyme that helps the body break down toxic substances in alcoholic drinks

  3. Impacts, Issues: Alcohol, Enzymes, and Your Liver • The liver plays a central role in alcohol metabolism • Consumption of too much alcohol, as in binge drinking, can lead to alcoholic hepatitis or alcoholic cirrhosis

  4. What Is Energy? • Capacity to do work • Forms of energy • Potential energy • Kinetic energy • Chemical energy

  5. 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

  6. ENERGY GAINED Sunlight energy reaches environments on Earth. Producers of nearly all ecosystems secure some and convert it to stored forms of energy. They and all other organisms convert stored energy to forms that can drive cellular work. ENERGY LOST Energy continually flows from the sun. producers ENERGY LOST With each conversion, there is a one-way flow of a bit of energy back to the environment. Nutrients cycle between producers and consumers. NUTRIENT CYCLING consumers Fig. 6-4, p.74

  7. 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

  8. Bozeman video—gibbsfree energy http://www.youtube.com/watch?v=DPjMPeU5OeM http://www.youtube.com/watch?v=JBmykor-2kU

  9. 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

  10. Participants in Metabolic Reactions • Energy carriers • Enzymes • Cofactors • Transport proteins • Reactants • Intermediates • Products

  11. The Role of ATP • Cells “earn” ATP in exergonic reactions • Cells “spend” ATP in endergonic reactions base three phosphate groups sugar Fig. 6-6a, p.96

  12. Endergonic Reactions • Energy input required • Product has more energy than starting substances glucose, a high energy product + 6O2 ENERGY IN 6 6 low energy starting substances 6 6

  13. Exergonic Reactions • Energy is released • Products have less energy than starting substance glucose, a high energy starting substance + 6O2 ENERGY OUT low energy products 6 6

  14. ATP/ADP Cycle ATP cellular work (e.g., synthesis, breakdown, or rearrangement of substances; contraction of muscle cells; active transport across a cell membrane) ATP reactions that release energy reactions that require energy ADP + Pi Fig. 6-7a, p.75

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

  16. 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.

  17. 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.

  18. BOZEMAN VIDEO--ENZYMES http://www.youtube.com/watch?v=ok9esggzN18

  19. 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

  20. How Catalase Works A hydrogen of the peroxide is attracted to histidine, an amino acid projecting into the cavity. One oxygen binds the iron. Hydrogen peroxide (H2O2) enters a catalase. It is the substrate for a reaction aided by an iron molecule in a heme group (red). This binding destabilizes the peroxide bond which breaks. Water (H2O) forms. In a later reaction, another H2O2 will pull the oxygen from iron, which will then be free to act again. Fig. 6-10b, p.97

  21. Induced-Fit Model • 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

  22. 2 types of inhibitors: • Competitive—competes with the substrate for the ACTIVE SITE • Noncompetitive (AKA allosteric)—inhibitor bonds to allosteric site (away from active site)

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

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

  25. cooperativity • When a substrate binds to the active site of one of the enzyme’s subunits causing the same effect on all of the enzyme’s subunits • This can “prime” an enzyme to start accepting more and more substrate

  26. 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

  27. 2 types of feedback: • Positive---Ex: contractions & childbirth • Negative—AKA antagonistic Ex: fever

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

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

  30. Effect of Temperature Fig. 6-13, p.81

  31. Effect of pH Fig. 6-14a, p.81

  32. 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

  33. Metabolic Pathways • Defined as enzyme-mediated sequences of reactions in cells • Biosynthetic (anabolic) – ex: photosynthesis • Degradative (catabolic) – ex: aerobic respiration

  34. Redox Reactions • Cells release energy efficiently by electron transfers, or oxidation-reduction reactions (“redox” reactions) • One molecule gives up electrons (is oxidized) and another gains them (is reduced) • Hydrogen atoms are commonly released at the same time, thus becoming H+

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

  36. Bioluminescence • An outcome of enzyme-mediated reactions that release energy as fluorescent light

  37. Bioluminescent Bacteria Fig. 6-19, p.103

  38. OTHER REVIEW VIDEOS: http://www.youtube.com/watch?v=NzxgpsW_rJI

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