1. Menu 1 Energy and Enzymes

2. Menu 2 Menu – Energy and Enzymes  Instructions Instructions  Energy Energy  Chemical Bonds Chemical Bonds  ATP ATP  Catabolic and anabolic reactions Catabolic and anabolic reactions  Enzymes Enzymes  Conditions that affect enzymatic reactions Conditions that affect enzymatic reactions  Regulation of enzyme activity Regulation of enzyme activity  Ribozymes Ribozymes  Metabolic pathways Metabolic pathways  Redox reactions Redox reactions  Coenzymes Coenzymes  Electron carriers Electron carriers Select a topic below.

3. Menu 3 Before you begin…  Some of the slide navigation functions require full screen mode. Select “Browse” or “View” from the menu above, then select “Full Screen”.  Use the arrow keys (  or  ) to advance the slides or go backwards. The left mouse button also advances slides. You can click anywhere on the screen. If you know the slide number, you can enter the number and press Enter to go directly to that slide. The slide number is at the bottom left of most slides. Press “Esc” to end the program.  There are 88 slides in this presentation. l This button ( ) always returns you to the previously-viewed slide.

4. Menu 4 Forms of Energy  These forms of energy are important to life: –chemical –radiant (examples: heat, light) –mechanical –electrical  Energy can be transformed from one form to another.  Chemical energy is the energy contained in the chemical bonds of molecules.  Radiant energy travels in waves and is sometimes called electromagnetic energy. An example is visible light.  Photosynthesis converts light energy to chemical energy.  Energy that is stored is called potential energy.

5. Menu 5 Laws of Thermodynamics  1st law: Energy cannot be created or destroyed. –Energy can be converted from one form to another. The sum of the energy before the conversion is equal to the sum of the energy after the conversion. –Example: A light bulb converts electrical energy to light energy and heat energy. Fluorescent bulbs produce more light energy than incandescent bulbs because they produce less heat.  2nd law: Some usable energy dissipates during transformations and is lost. –During changes from one form of energy to another, some usable energy dissipates, usually as heat. The amount of usable energy therefore decreases.

6. Menu 6 Energy is required to form bonds. Atoms or molecules Energy + Energy Larger molecule The energy that was used to form the bonds is now stored in this molecule.

7. Menu 7 Energy is released when bonds are broken. Menu

8. 8 Energy is released when bonds are broken. Energy When bonds break, energy is released. It may be in a form such as heat or light or it may be transferred to another molecule. Menu

9. 9 ATP (Simplified Drawing) A Base (adenine) Sugar (ribose) 3 phosphate groups

10. Menu 10 A ATP ATP Stores Energy The phosphate bonds are high-energy bonds. A Energy ADP + P i + Energy Breaking the bonds releases the energy.

11. Menu 11 ATP ADP + P i Energy (from glucose or other high- energy compounds) ATP is Recycled  ATP (Adenosine Triphosphate) is an energy-containing molecule used to supply the cell with energy. The energy used to produce ATP comes from glucose or other high-energy compounds.  ATP is continuously produced and consumed as illustrated below.  ADP + P i + Energy  ATP + H 2 O (Note: P i = phosphate group)

12. Menu 12 ATP ATPADP + P i Energy MenuATP Energy from breaking bonds in this molecule is used to form ATP.

13. Menu 13 ATP ATPADP + P i Energy Menu The energy in ATP can be used to form bonds in other molecules.

14. Menu 14 CH N C C C NH 2 N HC N N C C C C O C O P O P O P O CH 2 O O O O - O - O - - H OH H ATP (Adenosine Triphosphate) 3 phosphate groups Base (adenine) Ribose

15. Menu 15Phosphorylation  ATP is synthesized from ADP + P i. The process of synthesizing ATP is called phosphorylation.  Two kinds of phosphorylation are illustrated on the next several slides. –Substrate-Level Phosphorylation –Chemiosmotic Phosphorylation

16. Menu 16 Substrate-Level Phosphorylation ADP High-energy molecule A high-energy molecule (substrate) is used to transfer a phosphate group to ADP to form ATP.

17. Menu 17 Substrate-Level Phosphorylation ADP High-energy molecule A high-energy molecule (substrate) is used to transfer a phosphate group to ADP to form ATP. This bond will be broken, releasing energy.

18. Menu 18 Substrate-Level Phosphorylation ADP High-energy molecule A high-energy molecule (substrate) is used to transfer a phosphate group to ADP to form ATP. The energy released will be used to bond the phosphate group to ADP, forming ATP.

19. Menu 19 Substrate-Level Phosphorylation A high-energy molecule (substrate) is used to transfer a phosphate group to ADP to form ATP. Enzyme An enzyme is needed. ADP High-energy molecule

20. Menu 20 Substrate-Level Phosphorylation Breaking this bond will release energy.

21. Menu 21 Substrate-Level Phosphorylation The energy will be used to form this bond.

22. Menu 22 Substrate-Level Phosphorylation Low-energy moleculeATP The energy has been transferred from the high-energy molecule to ADP to produce ATP.

23. Menu 23 Mitochondrion Structure Cristae Matrix Intermembrane Space  This drawing shows a mitochondrion cut lengthwise to reveal its internal membrane.

24. H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Outside Intermembrane Space Matrix This drawing shows a close-up of a section of a mitochondrion. Matrix (inside) Chemiosmotic Phosphorylation Menu

25. Chemiosmotic Phosphorylation H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Matrix (inside) Menu Pumps within the membrane pump hydrogen ions from the matrix to the intermembrane space creating a concentration gradient. Outside Intermembrane Space Matrix

26. Chemiosmotic Phosphorylation H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Matrix (inside) Menu This process requires energy and will be discussed in the chapter on cellular respiration. Outside Intermembrane Space Matrix

27. H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Matrix (inside) Menu Chemiosmotic Phosphorylation A high concentration of hydrogen ions in the intermembrane space creates osmotic pressure. Outside Intermembrane Space Matrix

28. H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Matrix (inside) Menu Osmotic pressure forces the hydrogen ions through this protein (called ATP synthase) as they return to the matrix. Chemiosmotic Phosphorylation Outside Intermembrane Space Matrix

29. H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP ADP + P i H+H+ ATP synthase produces ATP by phosphorylating ADP. The energy needed to produce ATP comes from hydrogen ions forcing their way into the matrix as they pass through the ATP synthase (due to osmotic pressure). Matrix (inside) Menu Osmotic pressure forces the hydrogen ions through this protein (ATP synthase) as they return to the matrix. Chemiosmotic Phosphorylation Outside Intermembrane Space Matrix

30. Menu 30 Chemiosmotic Phosphorylation  Chemiosmotic phosphorylation (previous slide) is used by the mitochondrion to produce ATP. The energy needed to initially pump H + ions into the intermembrane space comes from glucose. The entire process is called cellular respiration and will be discussed in a later chapter.  The chloroplast also produces ATP by chemiosmotic phosphorylation. The energy needed to produce ATP comes from sunlight.

31. Menu 31 Chloroplast Structure  The chloroplast is surrounded by a double membrane.  Molecules that absorb light energy (photosynthetic pigments) are located on disk-shaped structures called thylakoids.  The interior portion is the stroma. Thylakoids Double membrane Stroma

32. Menu 32 H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ A Thylakoid (see previous slide) In order to synthesize ATP, hydrogen ions must first be pumped into the thylakoid. This process requires energy.

33. Menu 33 H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ A Thylakoid A concentration gradient of hydrogen ions is established. The osmotic pressure from this gradient can be used as an energy source for producing ATP.

34. Menu 34 H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ADP + P i ATP Chemiosmotic Phosphorylation ATP synthase produces ATP by phosphorylating ADP. The energy comes from hydrogen ions forcing their way into the stroma as they pass through the ATP synthase under pressure (osmotic pressure). Osmotic pressure forces hydrogen ions through this protein (ATP synthase) as they return to the stroma.

35. Menu 35Phosphorylation  We have just discussed two different forms of phosphorylation: –Substrate-level phosphorylation –Chemiosmotic phosphorylation  We saw that chemiosmotic phosphorylation occurred in both the mitochondria (during cellular respiration) and in the chloroplast (during photosynthesis). These two processes are sometimes given separate names: –Oxidative phosphorylation (in mitochondria) –Photophosphorylation (in chloroplast)

36. Menu 36 Catabolic and Anabolic Reactions  The energy-producing reactions within cells generally involve the breakdown of complex organic compounds to simpler compounds. These reactions release energy and are called catabolic reactions.  Anabolic reactions are those that consume energy while synthesizing compounds.  ATP produced by catabolic reactions provides the energy for anabolic reactions. Anabolic and catabolic reactions are therefore coupled (they work together) through the use of ATP.  Diagram: next slide

37. ATPADP + P i Energy Menu An anabolic reaction A catabolic reaction Catabolic and Anabolic Reactions

38. Menu 38 Energy Supplied Energy Released Anabolic Reactions Anabolic reactions consume energy. Substrates (Reactants) Products Menu

39. 39 Energy Supplied Catabolic reactions release energy. Catabolic Reactions Substrate (Reactant) When bonds are broken, energy is released. Menu Energy Released

40. Menu 40 Activation Energy Energy Supplied Activation Energy In either kind of reaction, additional energy must be supplied to start the reaction. This energy is called activation energy. Menu Energy Released

41. Menu 41 Activation Energy Energy Supplied Activation Energy An example of activation energy is the spark needed to ignite gasoline. Menu Energy Released

42. Menu 42 Enzymes Lower Activation Energy Energy Supplied Activation energy without enzyme Activation energy with enzyme Enzymes lower the amount of activation energy needed for a reaction. Menu Energy Released

43. Substrate Enzyme Active Site Enzyme-Substrate Complex Product Enzyme 1 2 3Enzymes Enzymes are organic catalysts. Menu

44. 44Enzymes  Catalysts are substances that speed up chemical reactions. Organic catalysts (contain carbon) are called enzymes.  Enzymes are specific for one particular reaction or group of related reactions.  Many reactions cannot occur without the correct enzyme present.  They are often named by adding "ase" to the name of the substrate. Example: Dehydrogenases are enzymes that remove hydrogen.

45. Menu 45 Induced Fit Theory  An enzyme-substrate complex forms when the enzyme’s active site binds with the substrate like a key fitting a lock.  The substrate molecule does not fit exactly in the active site. This induces a change in the enzymes conformation (shape) to make a closer fit.  After the reaction, the products are released and the enzyme returns to its normal shape.  Only a small amount of enzyme is needed because they can be used repeatedly.

46. Menu 46 Rate of Reaction  Reactions with enzymes are up to 10 billion times faster than those without enzymes.  Enzymes typically react with between 1 and 10,000 molecules per second. Fast enzymes catalyze up to 500,000 molecules per second.  Substrate concentration, enzyme concentration, Temperature, and pH affect the rate of enzyme reactions.

47. Menu 47 Substrate Concentration  At lower concentrations, the active sites on most of the enzyme molecules are not filled because there is not much substrate. Higher concentrations cause more collisions between the molecules. With more molecules and collisions, enzymes are more likely to encounter molecules of reactant.  The maximum velocity of a reaction is reached when the active sites are almost continuously filled. Increased substrate concentration after this point will not increase the rate. Reaction rate therefore increases as substrate concentration is increased but it levels off. Substrate Concentration Rate of Reaction

48. Menu 48 Enzyme Concentration  If there is insufficient enzyme present, the reaction will not proceed as fast as it otherwise would because there is not enough enzyme for all of the reactant molecules.  As the amount of enzyme is increased, the rate of reaction increases. If there are more enzyme molecules than are needed, adding additional enzyme will not increase the rate. Reaction rate therefore increases as enzyme concentration increases but then it levels off. Enzyme Concentration Rate of Reaction

49. Menu 49 Effect of Temperature on Enzyme Activity 30 40 50 Rate of Reaction Temperature

50. Menu 50 Effect of Temperature on Enzyme Activity 30 40 50 Rate of Reaction Temperature Increasing the temperature causes more collisions between substrate and enzyme molecules. The rate of reaction therefore increases as temperature increases.

51. Menu 51 Effect of Temperature on Enzyme Activity 30 40 50 Rate of Reaction Temperature Enzymes denature when the temperature gets too high. The rate of reaction decreases as the enzyme becomes nonfunctional.

52. Menu 52Temperature  Higher temperature causes more collisions between the atoms, ions, molecules, etc. It therefore increases the rate of a reaction. More collisions increase the likelihood that substrate will collide with the active site of the enzyme.  Above a certain temperature, activity begins to decline because the enzyme begins to denature (unfold).  The rate of chemical reactions therefore increases with temperature but then decreases. 30 40 50 Rate of Reaction Temperature

53. Menu 53Denaturation  If the hydrogen bonds within an enzyme are broken, the enzyme may unfold or take on a different shape. The enzyme is denatured.  A denatured enzyme will not function properly because the shape of the active site has changed.  If the denaturation is not severe, the enzyme may regain its original shape and become functional.  The following will cause denaturation: –Heat –Changes in pH –Heavy-metal ions (lead, arsenic, mercury) –Alcohol –UV radiation

54. Menu 54 Effect of pH on Enzyme Activity  Each enzyme has its own optimum pH. 2 3 4 5 6 7 8 9 Rate of Reaction pH Pepsin Trypsin

55. Menu 55pH  Each enzyme has an optimal pH. Pepsin, an enzyme found in the stomach, functions best at a low pH. Trypsin, found in the intestine, functions best at a neutral pH.  A change in pH can alter the ionization of the R groups of the amino acids. When the charges on the amino acids change, hydrogen bonding within the protein molecule change and the molecule changes shape. The new shape may not be effective.  The diagram shows that pepsin functions best in an acid environment. This makes sense because pepsin is an enzyme that is normally found in the stomach where the pH is low due to the presence of hydrochloric acid. Trypsin is found in the duodenum (small intestine), and therefore, its optimum pH is in the neutral range to match the pH of the duodenum. 2 3 4 5 6 7 8 9 Rate of Reaction pH Pepsin Trypsin

56. Menu 56 Metabolic Pathways  Metabolism refers to the chemical reactions that occur within cells.  Reactions occur in a sequence and a specific enzyme catalyzes each step.

57. Menu 57 Metabolic Pathways enzyme 1enzyme 2enzyme 3enzyme 4 F enzyme 5 A B C D E Notice that C can produce either D or F. This substrate has two different enzymes that work on it. Enzymes are very specific. In this case enzyme 1 will catalyze the conversion of A to B only.

58. Menu 58 A Cyclic Metabolic Pathway B C D F A E A + F  B B  C  D D  F + E In this pathway, substrate “A” enters the reaction. After several steps, product “E” is produced.

59. Menu 59 Regulation of Enzymes  The next several slides illustrate how cells regulate enzymes. For example, it may be necessary to decrease the activity of certain enzymes if the cell no longer needs the product produced by the enzymes.

60. Menu 60 Regulation of Enzymes Enzymes are proteins. Recall the central dogma: DNA mRNA Proteins Proteins can be regulated by making more or less of them as needed. The topic of regulating protein synthesis (manufacture) is deferred to a later chapter. genetic regulation regulation of enzymes already produced

61. Menu 61 Regulation of Enzymes genetic regulation regulation of enzymes already produced competitive Inhibition (illustrated on the next slide)

62. Menu 62 Competitive Inhibition In competitive inhibition, a similar-shaped molecule competes with the substrate for active sites.

63. Menu 63 Competitive Inhibition

64. Menu 64 Regulation of Enzymes genetic regulation regulation of enzymes already produced competitive inhibition noncompetitive Inhibition (see next slide)

65. Menu 65 Noncompetitive Inhibition  Another form of inhibition involves an inhibitor that binds to an allosteric site of an enzyme. An allosteric site is a different location than the active site.  The binding of an inhibitor to the allosteric site alters the shape of the enzyme, resulting in a distorted active site that does not function properly. Active siteInhibitorAltered active site Enzyme

66. Menu 66 Noncompetitive Inhibition  The binding of an inhibitor to an allosteric site is usually temporary. Poisons are inhibitors that bind irreversibly. For example, penicillin inhibits an enzyme needed by bacteria to build the cell wall. Bacteria growing (reproducing) without producing cell walls eventually rupture.

67. Menu 67 Regulation of Enzymes genetic regulation regulation of enzymes already produced competitive inhibition noncompetitive inhibition feedback inhibition (next slide)

68. Menu 68 Example of Feedback Inhibition Cold Thermostat Heater Heat inhibits In this example of feedback inhibition, heat (the product) inhibits its production. This keeps the temperature constant.

69. Menu 69 Enzyme regulation by negative feedback inhibition is similar to the thermostat example. As an enzyme's product accumulates, it turns off the enzyme just as heat causes a thermostat to turn off the production of heat. Feedback Inhibition A B C D enzyme 1enzyme 2enzyme 3 The goal of this hypothetical metabolic pathway is to produce chemical D from A. B and C are intermediates. The next several slides will show how feedback inhibition regulates the amount of D produced.

70. Menu 70 A B C D enzyme 1enzyme 2enzyme 3 Feedback Inhibition Enzyme 1 is structured in a way that causes it to interact with D. When the amount of D increases, the enzyme stops functioning. X The amount of B in the cell will decrease if enzyme 1 is inhibited. XX C and D will decrease because B is needed to produce C and C is needed to produce D.

71. Menu 71 Feedback Inhibition When the amount of D drops, enzyme 1 will no longer be inhibited. B, C, and D can now be synthesized. A B C D enzyme 1enzyme 2enzyme 3 X XX B CD

72. Menu 72 Feedback Inhibition As D begins to increase, it inhibits enzyme 1 again and the cycle repeats itself. A B C D enzyme 1enzyme 2enzyme 3 X

73. Menu 73Ribozymes  Ribozymes are molecules of RNA that function like enzymes, that is, they have an active site and increase the rate of specific chemical reactions.

74. Menu 74 Energy is transferred with electrons. Oxidized atom Electron is donated Energy is donated Reduced atom Electron is received Energy is received

75. Menu 75 Energy is transferred with electrons. Oxidized atom Electron is donated Energy is donated Reduced atom Electron is received Energy is received

76. Menu 76 Energy is transferred with electrons. Oxidized atom Electron is donated Energy is donated Reduced atom Electron is received Energy is received This atom served as an energy carrier. It picked up an electron from the atom on the left and gave it to the one on the right.

77. Menu 77 Oxidation and Reduction  Oxidation is the loss of electrons or hydrogen atoms. Oxidation reactions release energy.  Reduction is gain of electrons or hydrogen atoms and is associated with a gain of energy.  Oxidation and reduction occur together. When a molecule is oxidized, another must be reduced.  These coupled reactions are called oxidation-reduction or redox reactions.  Food is highly reduced (has many hydrogens). The chemical pathways in cells that produce energy for the cell oxidize the food (remove hydrogens), producing ATP.

78. Menu 78Cofactors  Many enzymes require a cofactor to assist in the reaction. These "assistants" are nonprotein and may be metal ions such as magnesium (Mg++), potassium (K+), and calcium (Ca++).  The cofactors bind to the enzyme and participate in the reaction by removing electrons, protons, or chemical groups from the substrate.

79. Menu 79Coenzymes  Cofactors that are organic molecules are coenzymes.  In oxidation-reduction reactions, coenzymes often remove electrons from the substrate and pass them to different enzymes.  In this way, coenzymes serve to carry energy in the form of electrons (or hydrogen atoms) from one compound to another.

80. Menu 80Coenzymes  Coenzymes are cofactors that are not protein.  They bind to the enzyme and also participate in the reaction by carrying electrons or hydrogen atoms. Enzyme Coenzyme

81. Menu 81 Vitamins are Coenzymes VitaminCoenzyme Name NiacinNAD + B 2 (riboflavin)FAD B 1 (thiamine)Thiamine pyrophosphate Pantothenic acidCoenzyme A (CoA) B 12 Cobamide coenzymes

82. Menu 82 Electron Carriers  Electron carriers function in photosynthesis and cellular respiration. Three major electron carriers are listed below.  Respiration –NAD + –FAD  Photosynthesis –NADP +

83. NAD + (Nicotinamide Adenine Dinucleotide) Organic Molecule + NAD + NAD + + 2H  NADH + H +  NAD + functions in cellular respiration by carrying two electrons. With two electrons, it becomes NADH.  NAD + oxidizes its substrate by removing two hydrogen atoms. One of the hydrogen atoms bonds to the NAD +. The electron from the other hydrogen atom remains with the NADH molecule but the proton (H + ) is released.  NAD + + 2H  NADH + H +  NADH can donate two electrons (one of them is a hydrogen atom) to another molecule. Menu

84. 84 NAD + + 2H  NADH + H + NADH + H + NAD + Energy + 2H Energy + 2H

85. Menu 85 FAD + 2H  FADH 2 FADH 2 FAD Energy + 2H Energy + 2H

86. Menu 86 FAD (flavin adenine dinucleotide)  FAD is reduced to FADH 2. It can transfer two electrons to another molecule.  FAD + 2H  FADH 2

87. Menu 87 NADP + + 2H  NADPH + H + NADPH + H + NADP + Energy + 2H Energy + 2H

88. Menu 88 NADP + (Nicotinamide Adenine Dinucleotide Phosphate)  NADP + + 2H  NADPH + H +  NADP + is similar to NAD + in that it can carry two electrons, one of them in a hydrogen atom, the other one comes from a hydrogen that is released as a hydrogen ion. (Click here to review NAD +.)Click here to review NAD +.  Electrons carried by NADPH in photosynthesis are ultimately used to reduce CO 2 to carbohydrate.

89. Menu 89 The End