Chapter 7 Energy transduction in cells.pptx

It covers the metabolism in cells

1. Chapter 7 Transduction of Energy in the cell 1 3/5/2017

2. 7.1. Cellular respiration Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose C 6 H 12 O 6 + 6 O 2  6 CO 2 + 6 H 2 O + Energy (ATP + heat) 2 3/5/2017

3. Redox Reactions: Oxidation and Reduction The transfer of electrons during chemical reactions releases energy stored in organic molecules This released energy is ultimately used to synthesize ATP Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 3 3/5/2017

4. Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions In oxidation , a substance loses electrons, or is oxidized In reduction , a substance gains electrons, or is reduced (the amount of positive charge is reduced) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 4 3/5/2017

5. Fig. 9-UN1 becomes oxidized (loses electron) becomes reduced (gains electron) 5 3/5/2017

6. Fig. 9-UN2 becomes oxidized becomes reduced 6 3/5/2017

7. The electron donor is called the reducing agent The electron receptor is called the oxidizing agent Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds An example is the reaction between methane and O 2 7 3/5/2017

8. Fig. 9-3 Reactants becomes oxidized becomes reduced Products Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxide Water 8 3/5/2017

9. 7.1.1. Source of high energy Energy for living things comes from food . Originally, the energy in food comes from the A) sun photosynthesis Eg plant, algae cyanobacteria . B) redox chemoautotroph Eg bacteria ) All energy is stored in the bonds of compounds— breaking the bond releases the energy When the cell has energy available it can store this energy by adding a phosphate group to ADP, producing ATP 9 3/5/2017

10. Metabolism Define : all chemical reactions Requirements Energy Enzymes Rate Limiting step Reaction time Types Anabolic Endergonic Dehydration Biosynthetic es Catabolic Exergonic Hydrolytic Degradative +/- metabolit 10 3/5/2017

11. Metabolism Relationships 11 3/5/2017

12. ATP: The Universal Energy Coupler 12 3/5/2017

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14. 14 Formation of ATP ATP can be formed by three different mechanisms: Substrate-level phosphorylation – transfer of phosphate group from a phosphorylated compound (substrate) directly to ADP Oxidative phosphorylation – series of redox reactions occurring during respiratory pathway Photophosphorylation – ATP is formed utilizing the energy of sunlight 3/5/2017

15. 7.1.2. Glycolysis : Embden- Meyerhoff Glycolytic Cytoplasm Anaerobic End products 2 Pyruvic acids 4-2 = 2 net ATP by substrate level phosphorylation 2 NADH 2 H 2 O 15 3/5/2017

16. Glycolysis 16 3/5/2017

17. Glycolysis cont’d 17 3/5/2017

18. Glycolysis cont’d 18 3/5/2017

19. Glycolysis cont’d 19 3/5/2017

20. Acetyl CoA Formation 20 3/5/2017

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22. 7.1.3.Citric acid cycle The citric acid cycle has eight steps, each catalyzed by a specific enzyme The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate , forming citrate The next seven steps decompose the citrate back to oxaloacetate , making the process a cycle 22 3/5/2017

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24. The Citrate Synthase Reaction (Step #1) The only cycle reaction with C-C bond formation Essentially irreversible process 24 3/5/2017

25. Isomerization of Citrate by Aconitase (Step #2) 25 3/5/2017

26. The Isocitrate Dehydrogenase Reaction (Step #3) Oxidation of the alcohol to ketone involves the transfer of a hydride from the C-H of the alcohol to the nicotinamide cofactor – 3 step mechanism 26 3/5/2017

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29. Oxidation of - ketoglutarate (Step #4) 29 3/5/2017

30. Substrate-Level Phosphorylation (Step #5) 30 3/5/2017

31. Succinate Dehydrogenase (Step #6) 31 3/5/2017

32. Hydration of Fumarate to Malate (Step #7) 32 3/5/2017

33. Oxidation of Malate to Oxaloacetate (Step #8) 33 3/5/2017

34. Krebs Cycle Metabolites For every AcetylCoA 2 CO2 3 NADH 1 FADH2 1 ATP (substrate level phosphorylation from GTP) Regenerates CoA Oxaloacetic acid 34 3/5/2017

35. Role of the Citric Acid Cycle in Anabolism 35 3/5/2017

36. 7.1.4. Electron transport system Oxidation–reduction enzymes (proteins) NADH dehydrogenases, flavoproteins , iron–sulfur proteins cytochromes 2 . Nonprotein electron carriers quinones 36 3/5/2017

37. COMPLEX I NADH ( nicotinamide adenine dinucleotide reduced form) is oxidized to NAD+, reducing FMN ( flavin mononucleotide) to FMNH2 in one two-electron site The next electron carrier is a Fe-S cluster, which can only accept one electron at a time to reduce the ferric ion into a ferrous ion. Conveniently, FMNH2 can only be oxidized in two one-electron steps, through a semiquinone intermediate. 37 3/5/2017

38. COMPEX I contd . The electron thus travels from the FMNH2 to the Fe-S cluster, then from the Fe-S cluster to the oxidized Q to give the free-radical ( semiquinone ) form of Q. This happens again to reduce the semiquinone form to the ubiquinol form, QH2. During this process, four protons are translocated across the inner mitochondrial membrane, from the matrix to the intermembrane space This creates a proton gradient that will be later used to generate ATP through oxidative phosphorylation . 38 3/5/2017

39. COMPLEX II Complex II ( succinate dehydrogenase ) is not a proton pump. It serves to funnel additional electrons into the quinone pool (Q) by removing electrons from succinate and transferring them (via FAD ) to Q. Other electron donors (e.g. fatty acids and glycerol 3-phosphate) also funnel electrons into Q (via FAD), again without producing a proton gradient. 39 3/5/2017

40. COMPLEX III Complex III ( cytochrome bc1 complex ) removes in a stepwise fashion two electrons from QH2 and transfers them to two molecules of cytochrome c , a water-soluble electron carrier located on the outer surface of the membrane. At the same time, it moves four protons across the membrane, producing a proton gradient. When electron transfer is hindered (by a high membrane potential, point mutations or respiratory inhibitors such as antimycin A), Complex III may leak electrons to oxygen resulting in the formation of a superoxide. 40 3/5/2017

41. COMPLEX IV Complex IV ( cytochrome c oxidase ) removes four electrons from four molecules of cytochrome c and transfers them to molecular oxygen (O 2 ), producing two molecules of water (H 2 O). At the same time, it moves four protons across the membrane, producing a proton gradient. 41 3/5/2017

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43. 7.1.5. The chemoosmosis model and oxidation phosphorylation Chemiosmosis – as the electron transport carriers shuttle electrons, they actively pump hydrogen ions (protons) across the membrane setting up a gradient of hydrogen ions - proton motive force . Hydrogen ions diffuse back through the ATP synthase complex causing it to rotate, causing a 3-dimensional change resulting in the production of ATP. 43 3/5/2017

44. As electrons flow through complexes of ETC, protons are translocated from matrix into the intermembrane space. The free energy stored in the proton concentration gradient is tapped as protons reenter the matrix via ATP synthase . As result ATP is formed from ADP and P i . 44 3/5/2017

45. Electrons of NADH or FADH 2 are used to reduce molecular oxygen to water. A large amount of free energy is liberated. The electrons from NADH and FADH 2 are not transported directly to O 2 but are transferred through series of electron carriers that undergo reversible reduction and oxidation. 45 3/5/2017

46. The flow of electrons through carriers leads to the pumping of protons out of the mitochondrial matrix. The resulting distribution of protons generates a pH gradient and a transmembrane electrical potential that creates a protonmotive force. 46 3/5/2017

47. ATP is synthesized when protons flow back to the mitochondrial matrix through an enzyme complex ATP synthase . The oxidation of fuels and the phosphorylation of ADP are coupled by a proton gradient across the inner mitochondrial membrane. Oxidative phosphorylation is the process in which ATP is formed as a result of the transfer of electrons from NADH or FADH 2 to O 2 by a series of electron carriers . 47 3/5/2017

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49. How Are the Electrons of Cytosolic NADH Fed into Electron Transport? Most NADH used in electron transport is produced in mitochondrial matrix Cytosolic NADH produced in glycolysis doesn't cross the inner mitochondrial membrane "Shuttle systems" effect electron movement without actually carrying NADH Glycerophosphate shuttle stores electrons in glycerol-3-P, which transfers electrons to FAD Malate-aspartate shuttle uses malate to carry electrons across the membrane 49 3/5/2017

50. Glycerol 3-phosphate shuttle 50 3/5/2017

51. Malate-aspartate shuttle 51 3/5/2017

52. 7.1.6. Anaerobic respiration path way Anaerobic Respiration Functions like aerobic respiration except it utilizes oxygen containing ions or others, rather than free oxygen, as the final electron acceptor in MICROBES Nitrate (NO 3 - ) and nitrite (NO 2 - ) Most obligate anaerobes use the H + generated during glycolysis and TCA to reduce some compound other than O 2 . 52 3/5/2017

53. 53 Fermentation Incomplete oxidation of glucose or other carbohydrates in the absence of oxygen Uses organic compounds as terminal electron acceptors Yields a small amount of ATP Production of ethyl alcohol by yeasts acting on glucose Formation of acid, gas and other products by the action of various bacteria on pyruvic acid 3/5/2017

54. Glucose 2 Pyruvate 2 NAD + 2 NADH 2 ADP 2 ATP 2 Ethanol 2 Acetylaldehyde 2 CO 2 Alcohol Fermentation in Yeast 54 3/5/2017

55. Glucose 2 Pyruvate 2 NAD + 2 NADH 2 ADP 2 ATP 2 Lactate Pyruvate accepts electrons from NADH Lactic Acid Fermentation in Humans 55 3/5/2017

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57. FATTY ACIDS OXIDATION A fatty acid contains a long hydrocarbon chain and a terminal carboxylate group . The hydrocarbon chain may be saturated (with no double bond) or may be unsaturated (containing double bond). 57 3/5/2017

58. FUNCTIONS OF FATTY ACIDS Fatty acids have four major physiological roles. 1) Fatty acids are building blocks of phospholipids and glycolipids . 2) Many proteins are modified by the  covalent attachment of fatty acids, which target them to membrane locations 3) Fatty acids are fuel molecules . They are stored as  triacylglycerols . Fatty acids mobilized from triacylglycerols are oxidized to meet the energy needs of a cell or organism. 4) Fatty acid derivatives serve as hormones and intracellular messengers   e.g. steroids, sex hormones and prostaglandins. 58 3/5/2017

59. TRIGLYCERIDES Triglycerides are a highly concentrated stores of energy because they are  reduced  and  anhydrous . The yield from the complete oxidation of fatty acids is about 9 kcal g-1 (38 kJ g-1) Triacylglycerols are nonpolar, and are stored in a nearly anhydrous form, whereas much more polar proteins and carbohydrates are more highly hydrated. 59 3/5/2017

60. TRIGLYCERIDES V/S GLYCOGEN A gram of nearly anhydrous fat stores more than six times as much energy as a gram of hydrated glycogen , which is likely the reason that triacylglycerols rather than glycogen were selected in evolution as the major energy reservoir. The glycogen and glucose stores provide enough energy to sustain biological function for about 24 hours, whereas the Triacylglycerol stores allow survival for several weeks . 60 3/5/2017

61. PROVISION OF FATTY ACIDS FROM ADIPOSE TISSUE The triacylglycerols are degraded to fatty acids and glycerol by hormone sensitive lipase.The released fatty are transported to the energy-requiring tissues. 61 3/5/2017

62. TRANSPORTATION OF FREE FATTY ACIDS Free fatty acids—also called unesterified (UFA) or nonesterified (NEFA) fatty acids—are fatty acids that are in the unesterified state.  In plasma, longer-chain FFA are combined with  albumin,   and in the cell they are attached to a  fatty acid-binding protein. Shorter-chain fatty acids are more water-soluble and exist as the un-ionized acid or as a fatty acid anion. By these means, free fatty acids are made accessible as a fuel in other tissues. 62 3/5/2017

63. TYPES OF FATTY ACID OXIDATION Fatty acids can be oxidized by- 1 ) Beta oxidation-   Major mechanism, occurs in the mitochondria  matrix. 2-C units are released as acetyl CoA per cycle. 2) Alpha oxidation - Predominantly takes place in brain and liver, one carbon is lost in the form of CO2 per cycle. 3) Omega oxidation-  Minor mechanism, but becomes important in conditions of impaired beta oxidation 4) Peroxisomal oxidation-  Mainly for the trimming of very long chain fatty acids. 63 3/5/2017

64. BETA OXIDATION Overview of beta oxidation  A saturated acyl Co A is degraded by a recurring sequence of four reactions: 1) Oxidation by flavin adenine dinucleotide (FAD) 2) Hydration, 3) Oxidation by NAD + , and 4) Thiolysis by Co ASH 64 3/5/2017

65. BETA OXIDATION The fatty acyl chain is shortened by two carbon atoms as a result of these reactions, FADH2, NADH, and acetyl Co A are generated. Because oxidation is on the β carbon and the chain is broken between the α (2)- and β (3)-carbon atoms—hence the name – β oxidation . 65 3/5/2017

66. ACTIVATION OF FATTY ACIDS Fatty acids must first be converted to an active intermediate before they can be catabolized. This is the only step in the complete degradation of a fatty acid that requires energy from ATP. The activation of a fatty acid is accomplished in two steps- 66 3/5/2017

67. STEPS OF BETA OXIDATION Step-1 Dehydrogenation - The first step is the removal of two hydrogen atoms from the 2(α)- and 3(β)-carbon atoms, catalyzed by  acyl-CoA dehydrogenase  and requiring FAD. This results in the formation of Δ 2 - trans -enoyl-CoA and FADH 2 . 67 3/5/2017

68. STEPS OF BETA OXIDATION Electrons from the FADH2 prosthetic group of the reduced acyl CoA dehydrogenase are transferred to electron-transferring   flavoprotein  (ETF). ETF donates electrons to  ETF: ubiquinone reductase , an iron-sulfur protein . Ubiquinone is thereby reduced to ubiquinol , which delivers its high-potential electrons to the second proton-pumping site of the respiratory chain.  68 3/5/2017

69. STEPS OF BETA OXIDATION Step-2- Hydration Water is added to saturate the double bond and form 3-hydroxyacyl-CoA, catalyzed by Δ  2 -enoyl-CoA hydratase. 69 3/5/2017

70. STEPS OF BETA OXIDATION Step-3- dehydrogenation- The 3-hydroxy derivative undergoes further dehydrogenation on the 3-carbon catalyzed by L(+)-3-hydroxyacyl-CoA dehydrogenase  to form the corresponding 3-ketoacyl-CoA compound. In this case, NAD +  is the coenzyme involved. 70 3/5/2017

71. STEPS OF BETA OXIDATION Step-4- Thiolysis-   3-ketoacyl-CoA is split at the 2,3- position by thiolase  (3-ketoacyl-CoA-thiolase), forming acetyl-CoA and a new acyl-CoA two carbons shorter than the original acyl-CoA molecule. 71 3/5/2017

72. STEPS OF BETA OXIDATION The acyl-CoA formed in the cleavage reaction reenters the oxidative pathway at reaction 2. Since acetyl-CoA can be oxidized to CO 2  and water via the citric acid cycle the complete oxidation of fatty acids is achieved  72 3/5/2017

73. BETA OXIDATION The overall reaction can be represented as follows- 73 3/5/2017

74. BETA OXIDATION- ENERGY YIELD Energy yield by the complete oxidation of one mol of Palmitic acid- The degradation of palmitoyl CoA (C16-acyl Co A) requires seven reaction cycles. In the seventh cycle, the C4-ketoacyl CoA is thiolyzed to two molecules of acetyl CoA. 106 (129 As per old concept) ATP are produced by the complete oxidation of one mol of Palmitic acid. 74 3/5/2017

75. MINOR PATHWAYS OF FATTY ACID OXIDATION 1 ) α- Oxidation- Oxidation occurs at C-2 instead of C-3 , as in β oxidation 2) ω- Oxidation – Oxidation occurs at the methyl end of the fatty acid molecule. 3) Peroxisomal fatty acid oxidation- Occurs for the chain shortening of very long chain fatty acids. 3/5/2017 75

76. α - OXIDATION OF FATTY ACIDS Takes place   in the microsomes of brain and liver , Involves decarboxylation process for the removal of single carbon atom at one time with the resultant production of an odd chain fatty acid that can be subsequently oxidized by beta oxidation for energy production. It is strictly an aerobic process. No prior activation of the fatty acid is required. The process involves hydroxylation of the alpha carbon with a specific α-hydroxylase that requires Fe ++  and vitamin C/FH4 as cofactors. 3/5/2017 76

77. Phytanic acid is oxidized by Phytanic acid α oxidase (α- hydroxylase enzyme) to yield CO2 and odd chain fatty acid Pristanic acid that can be subsequently oxidized by beta oxidation. 3/5/2017 77

78. 7.2.Photosynthesis An anabolic, endergonic, carbon dioxide (CO 2 ) requiring process that uses light energy (photons) and water (H 2 O) to produce organic macromolecules (glucose). 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 glucose SUN photons 3/5/2017 78

79. Mesophyll Cell Cell Wall Nucleus Chloroplast Central Vacuole 3/5/2017 79

80. Chloroplasts Structure is very similar to mitochondria Probably evolved from a cyanobacterium incorporated into a non-photosynthetic eukaryote (symbiosis) In eukaryotes , the light reaction occurs in thylakoid membrane In prokaryotes , the light reaction occurs in: Inner (plasma) membrane In “ chromatophores ” Invaginations of inner membrane In eukaryotes, the dark reaction occurs in the stroma 3/5/2017 80

81. Chloroplast Organelle where photosynthesis takes place. Granum Thylakoid Stroma Outer Membrane Inner Membrane 3/5/2017 81

82. Thylakoid Thylakoid Membrane Thylakoid Space Granum 3/5/2017 82

83. Chlorophyll Molecules Located in the thylakoid membranes . Chlorophyll have Mg + in the center. Chlorophyll pigments harvest energy (photons) by absorbing certain wavelengths ( blue-420 nm and red-660 nm are most important). Plants are green because the green wavelength is reflected , not absorbed . 3/5/2017 83

84. Wavelength of Light (nm) 400 500 600 700 Short wave Long wave (more energy) (less energy) 3/5/2017 84

85. Absorption of Chlorophyll wavelength Absorption violet blue green yellow orange red 3/5/2017 85

86. Fall Colors In addition to the chlorophyll pigments, there are other pigments present. During the fall, the green chlorophyll pigments are greatly reduced revealing the other pigments . Carotenoids are pigments that are either red or yellow . 3/5/2017 86

87. Redox Reaction The transfer of one or more electrons from one reactant to another . Two types: 1. Oxidation 2. Reduction 3/5/2017 87

88. Oxidation Reaction The loss of electrons from a substance . Or the gain of oxygen . glucose 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 Oxidation 3/5/2017 88

89. Reduction Reaction The gain of electrons to a substance . Or the loss of oxygen . glucose 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 Reduction 3/5/2017 89

90. Breakdown of Photosynthesis Two main parts (reactions). 1. Light Reaction or Light Dependent Reaction Produces energy from solar power (photons) in the form of ATP and NADPH . 3/5/2017 90

91. Breakdown of Photosynthesis 2. Calvin Cycle or Light Independent Reaction or Carbon Fixation or C 3 Fixation Uses energy (ATP and NADPH) from light rxn to make sugar (glucose). 3/5/2017 91

92. 1. Light Reaction (Electron Flow) Occurs in the Thylakoid membranes During the light reaction , there are two possible routes for electron flow . A. Cyclic Electron Flow B. Noncyclic Electron Flow 3/5/2017 92

93. A. Cyclic Electron Flow Occurs in the thylakoid membrane . Uses Photosystem I only P700 reaction center- chlorophyll a Uses Electron Transport Chain (ETC) Generates ATP only ADP + ATP P 3/5/2017 93

94. A. Cyclic Electron Flow P700 Primary Electron Acceptor e - e - e - e - ATP produced by ETC Photosystem I Accessory Pigments SUN Photons 3/5/2017 94

95. B. Noncyclic Electron Flow Occurs in the thylakoid membrane Uses PS II and PS I P680 rxn center (PSII) - chlorophyll a P700 rxn center (PS I) - chlorophyll a Uses Electron Transport Chain (ETC) Generates O 2 , ATP and NADPH 3/5/2017 95

96. B. Noncyclic Electron Flow P700 Photosystem I P680 Photosystem II Primary Electron Acceptor Primary Electron Acceptor ETC Enzyme Reaction H 2 O 1/2O 2 + 2H + ATP NADPH Photon 2e - 2e - 2e - 2e - 2e - SUN Photon 3/5/2017 96

97. B. Noncyclic Electron Flow ADP +  ATP NADP + + H  NADPH Oxygen comes from the splitting of H 2 O , not CO 2 H 2 O  1/2 O 2 + 2H + (Reduced) P (Reduced) (Oxidized) 3/5/2017 97

98. Chemiosmosis Powers ATP synthesis . Located in the thylakoid membranes . Uses ETC and ATP synthase (enzyme) to make ATP . Photophosphorylation: addition of phosphate to ADP to make ATP . 3/5/2017 98

99. Chemiosmosis H + H + ATP Synthase H + H + H + H + H + H + high H + concentration H + ADP + P ATP PS II PS I E T C low H + concentration H + Thylakoid Space Thylakoid SUN (Proton Pumping) 3/5/2017 99

100. Calvin Cycle Carbon Fixation (light independent rxn). C 3 plants (80% of plants on earth). Occurs in the stroma . Uses ATP and NADPH from light rxn. Uses CO 2 . To produce glucose : it takes 6 turns and uses 18 ATP and 12 NADPH . 3/5/2017 100