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Metabolism and Energy Flow
- 1. Albia Dugger • Miami Dade College Cecie Starr Christine Evers Lisa Starr www.cengage.com/biology/starr Chapter 5 Ground Rules of Metabolism (Sections 5.1 - 5.4)
- 2. 5.1 A Toast to Alcohol Dehydrogenase • Metabolic processes build and break down organic molecules such as ethanol and other toxins • Alcohol breakdown directly damages liver cells, and interferes with normal processes of metabolism • Currently the most serious drug problem on college campuses is binge drinking
- 3. Alcohol Metabolism • The enzyme alcohol dehydrogenase helps the liver break down toxic alcohols (ethanol)
- 4. 5.2 Energy and the World of Life • There are many forms of energy: • Kinetic energy, potential energy • Light, heat, electricity, motion • Energy cannot be created or destroyed (first law of thermodynamics) • Energy can be converted from one form to another and thus transferred between objects or systems
- 5. Energy Disperses • Energy tends to disperse spontaneously (second law of thermodynamics) • A bit disperses at each energy transfer, usually as heat • Entropy is a measure of how dispersed the energy of a system has become
- 6. Key Terms • energy • The capacity to do work • kinetic energy • The energy of motion • entropy • Measure of how much the energy of a system is dispersed
- 7. Key Terms • first law of thermodynamics • Energy cannot be created or destroyed • second law of thermodynamics • Energy tends to disperse spontaneously
- 9. Entropy • Entropy tends to increase, but the total amount of energy in any system always stays the same
- 10. Fig. 5.3, p. 76 Entropy Time heat energy Stepped Art Entropy
- 11. Work • Work occurs as a result of an energy transfer • A plant converts light energy to chemical energy in photosynthesis • Most other cellular work occurs by transfer of chemical energy from one molecule to another (such as transferring chemical energy from ATP to other molecules)
- 12. Energy’s One-Way Flow • Living things maintain their organization only as long as they harvest energy from someplace else • Energy flows in one direction through the biosphere, starting mainly from the sun, then into and out of ecosystems • Producers and then consumers use energy to assemble, rearrange, and break down organic molecules that cycle among organisms throughout ecosystems
- 13. Energy Conversion • It takes 10,000 pounds of feed to raise a 1,000- pound steer • About 15% of energy in food builds body mass; the rest is lost as heat during energy conversions
- 14. Energy Flow • Energy flows from the environment into living organisms, and back to the environment • Materials cycle among producers and consumers
- 15. Fig. 5.5, p. 77 Consumers animals, most fungi, many protists, bacteria nutrient cycling Producers plants and other self-feeding organisms sunlight energy Energy Flow
- 16. Animation: One-Way Energy Flow and Materials Cycling
- 17. Potential Energy • Energy’s spontaneous dispersal is resisted by chemical bonds • Energy in chemical bonds is a type of potential energy, because it can be stored • potential energy • Stored energy
- 18. Key Concepts • Energy Flow • Organisms maintain their organization only by continually harvesting energy from their environment • ATP couples reactions that release usable energy with reactions that require it
- 19. Animation: Energy Changes in Chemical Work
- 20. 5.3 Energy in the Molecules of Life • Every chemical bond holds energy – the amount of energy depends on which elements are taking part in the bond • Cells store and retrieve free energy by making and breaking chemical bonds in metabolic reactions, in which reactants are converted to products
- 21. Key Terms • reaction • Process of chemical change • reactant • Molecule that enters a reaction • product • A molecule that remains at the end of a reaction
- 22. Chemical Bookkeeping • In equations that represent chemical reactions, reactants are written to the left of an arrow that points to the products • A number before a formula indicates the number of molecules • The same number of atoms that enter a reaction remain at the reaction’s end
- 24. 2H2O (water) Fig. 5.6, p. 78 Stepped Art Reactants 4 hydrogen atoms + 2 oxygen atoms Products 4 hydrogen atoms + 2 oxygen atoms 2H2 (hydrogen) O2 (oxygen) Chemical Bookkeeping
- 26. Energy In, Energy Out • In most reactions, free energy of reactants differs from free energy of products • Reactions in which reactants have less free energy than products are endergonic – they will not proceed without a net energy input • Reactions in which reactants have greater free energy than products are exergonic – they end with a net release of free energy
- 27. Key Terms • endergonic • “Energy in” • Reaction that converts molecules with lower energy to molecules with higher energy • Requires net input of free energy to proceed • exergonic • “Energy out” • Reaction that converts molecules with higher energy to molecules with lower energy • Ends with a net release of free energy
- 28. Energy In, Energy Out
- 29. Fig. 5.7, p. 78 Freeenergy energy out energy in 2H2O O22H2 1 2 2H2O Energy In, Energy Out
- 30. Why Earth Does Not Go Up in Flames • Earth is rich in oxygen—and in potential exergonic reactions; why doesn’t it burst into flames? • Luckily, energy is required to break chemical bonds of reactants, even in an exergonic reaction • activation energy • Minimum amount of energy required to start a reaction • Keeps exergonic reactions from starting spontaneously
- 32. Fig. 5.8, p. 79 O2 Freeenergy 2H2 Activation energy Products: 2H2ODifference between free energy of reactants and products Reactants: Activation Energy
- 34. ATP—The Cell’s Energy Currency • ATP is the main currency in a cell’s energy economy • ATP (Adenosine triphosphate) • Nucleotide with three phosphate groups linked by high- energy bonds • An energy carrier that couples endergonic with exergonic reactions in cells
- 35. ATP
- 36. Fig. 5.9a, p. 79 A Structure of ATP. ribose adenine three phosphate groups ATP
- 37. Phosphorylation • When a phosphate group is transferred from ATP to another molecule, energy is transferred along with the phosphate • Phosphate-group transfers (phosphorylations) to and from ATP couple exergonic reactions with endergonic ones • phosphorylation • Addition of a phosphate group to a molecule • Occurs by the transfer of a phosphate group from a donor molecule such as ATP
- 38. ATP and ADP
- 39. Fig. 5.9b, p. 79 B After ATP loses one phosphate group, the nucleotide is ADP (adenosine diphosphate); after losing two phosphate groups, it is AMP (adenosine monophosphate) ribose adenine AMP ATPADP ATP and ADP
- 40. ATP/ADP Cycle • Cells constantly use up ATP to drive endergonic reactions, so they constantly replenish it by the ATP/ADP cycle • ATP/ADP cycle • Process by which cells regenerate ATP • ADP forms when ATP loses a phosphate group, then ATP forms again as ADP gains a phosphate group
- 41. ATP/ADP Cycle
- 42. Fig. 5.9c, p. 79 energy out ADP + phosphate energy in C ATP forms by endergonic reactions. ADP forms again when ATP energy is transferred to another molecule along with a phosphate group. Energy from such transfers drives cellular work. ATP/ADP Cycle
- 44. 5.4 How Enzymes Work • Enzymes makes a reaction run much faster than it would on its own, without being changed by the reaction • catalysis • The acceleration of a reaction rate by a molecule that is unchanged by participating in the reaction • Most enzymes are proteins, but some are RNAs
- 45. Substrates • Each enzyme recognizes specific reactants, or substrates, and alters them in a specific way • substrate • A molecule that is specifically acted upon by an enzyme
- 46. Active Sites • Enzyme specificity occurs because an enzyme’s polypeptide chains fold up into one or more active sites • An active site is complementary in shape, size, polarity, and charge to the enzyme’s substrate • active site • Pocket in an enzyme where substrates bind and a reaction occurs
- 47. An Active Site
- 48. Fig. 5.10a, p. 80 An Active Site
- 49. Fig. 5.10a, p. 80 active site enzyme A Like other enzymes, hexokinase’s active sites bind and alter specific substrates. A model of the whole enzyme is shown to the left. An Active Site
- 50. Fig. 5.10b, p. 80 An Active Site
- 51. Fig. 5.10b, p. 80 reactant(s) B A close-up shows glucose and phosphate meeting inside the enzyme’s active site. The microenvironment of the site favors a reaction between the two substrate molecules. An Active Site
- 52. Fig. 5.10c, p. 80 An Active Site
- 53. Fig. 5.10c, p. 80 product(s) C Here, the glucose has bonded with the phosphate. The product of this reaction, glucose-6-phosphate, is shown leaving the active site. An Active Site
- 54. Lowering Activation Energy • Enzymes lower activation energy in four ways: • Bringing substrates closer together • Orienting substrates in positions that favor reaction • Inducing the fit between a substrate and the enzyme’s active site (induced-fit model) • Shutting out water molecules • induced-fit model • Substrate binding to an active site improves the fit between the two
- 56. Fig. 5.11, p. 80 Freeenergy Reactants Products Transition state Activation energy with enzyme Activation energy without enzyme Time Lowering Activation Energy
- 57. Animation: Enzymes and Activation Energy
- 58. Effects of Temperature, pH, and Salinity • Each type of enzyme works best within a characteristic range of temperature, pH, and salt concentration: • Adding heat energy boosts free energy, increasing reaction rate (within a given range) • Most human enzymes have an optimal pH between 6 and 8 (e.g. pepsin functions only in stomach fluid, pH 2) • Too much or too little salt disrupts hydrogen bonding that holds an enzyme in its three-dimensional shape
- 60. Fig. 5.12, p. 81 Temperature Enzymeactivity temperature- sensitive tyrosinase normal tyrosinase 40°C (104°F)30°C (86°F)20°C (68°F) Enzymes and Temperature
- 61. Animation: Enzymes and Temperature
- 62. Enzymes and pH
- 63. Fig. 5.13, p. 81 pH trypsin glycogen phosphorylase pepsin Enzymeactivity 1 2 3 4 5 6 7 8 9 10 11 Enzymes and pH
- 64. Help From Cofactors • Most enzymes require cofactors, which are metal ions or organic coenzymes in order to function • cofactor • A metal ion or a coenzyme that associates with an enzyme and is necessary for its function • coenzyme • An organic molecule that is a cofactor
- 65. Coenzymes and Cofactors • Coenzymes may be modified by taking part in a reaction • Example: NAD+ becomes NADH by accepting electrons and a hydrogen atom in a reaction • Cofactors are metal ions • Example: The iron atom at the center of each heme • In the enzyme catalase, iron pulls on the substrate’s electrons, which brings on the transition state
- 66. Antioxidants • Cofactors in some antioxidants help them stop reactions with oxygen that produce free radicals (harmful atoms or molecules with unpaired electrons) • Example: Catalase is an antioxidant • antioxidant • Substance that prevents molecules from reacting with oxygen
- 67. Key Concepts • How Enzymes Work • Enzymes tremendously increase the rate of metabolic reactions • Cofactors assist enzymes, and environmental factors such as temperature, salt, and pH can influence enzyme function
- 68. Animation: How Catalase Works
Editor's Notes
- Figure 5.1 Alcohol metabolism. Alcohol dehydrogenase helps the body break down toxic alcohols such as ethanol. This enzyme makes it possible for humans to drink beer, wine, and other alcoholic beverages
- Figure 5.2 Demonstration of a familiar type of energy: motion, or kinetic energy.
- Figure 5.3 Entropy. Entropy tends to increase, but the total amount of energy in any system always stays the same
- Figure 5.3 Entropy. Entropy tends to increase, but the total amount of energy in any system always stays the same
- Figure 5.4 It takes more than 10,000 pounds of soybeans and corn to raise a 1,000-pound steer. Where do the other 9,000 pounds go? About half of the steer’s food is indigestible. The animal’s body breaks down molecules in the remaining half to access energy stored in chemical bonds. Only about 15% of that energy goes toward building body mass. The rest is lost during energy conversions, as heat.
- Figure 5.5 Energy flows from the environment into living organisms, and then back to the environment. The flow drives a cycling of materials among producers and consumers.
- Figure 5.6 Chemical bookkeeping. In equations that represent chemical reactions, reactants are written to the left of an arrow that points to the products. A number before a formula indicates the number of molecules. Atoms shuffle around in a reaction, but they never disappear: The same number of atoms that enter a reaction remain at the reaction’s end.
- Figure 5.7 Energy inputs and outputs in chemical reactions. 1 Endergonic reactions convert molecules with lower energy to molecules with higher energy, so they require a net energy input in order to proceed. 2 Exergonic reactions convert molecules with higher energy to molecules with lower energy, so they end with a net energy output.
- Figure 5.8 Activation energy. Most reactions will not begin without an input of activation energy, which is shown here as a bump in an energy hill. In this example, the reactants have more energy than the products. Activation energy keeps this and other exergonic reactions from starting spontaneously.
- Figure 5.9 ATP, the energy currency of cells.
- Figure 5.9 ATP, the energy currency of cells.
- Figure 5.9 ATP, the energy currency of cells.
- Figure 5.10 An example of an active site. This one is in a hexokinase, an enzyme that phosphorylates glucose and other six-carbon sugars.
- Figure 5.10 An example of an active site. This one is in a hexokinase, an enzyme that phosphorylates glucose and other six-carbon sugars.
- Figure 5.10 An example of an active site. This one is in a hexokinase, an enzyme that phosphorylates glucose and other six-carbon sugars.
- Figure 5.10 An example of an active site. This one is in a hexokinase, an enzyme that phosphorylates glucose and other six-carbon sugars.
- Figure 5.10 An example of an active site. This one is in a hexokinase, an enzyme that phosphorylates glucose and other six-carbon sugars.
- Figure 5.10 An example of an active site. This one is in a hexokinase, an enzyme that phosphorylates glucose and other six-carbon sugars.
- Figure 5.11 An enzyme enhances the rate of a reaction by lowering its activation energy.
- Figure 5.12 Enzymes and temperature. Tyrosinase is involved in the production of melanin, a black pigment in skin cells. The form of this enzyme in Siamese cats is inactive above about 30ｰC (86ｰF), so the warmer parts of the cat’s body end up with less melanin, and lighter fur.
- Figure 5.13 Enzymes and pH. Left, how pH affects three enzymes. Right, carnivorous plants of the genus Nepenthes grow in nitrogen-poor habitats. They secrete acids and protein-digesting enzymes into a fluid–filled cup that consists of a modified leaf. The enzymes release nitrogen from insects that are attracted to odors from the fluid and then drown in it. One of these enzymes functions best at pH 2.6.