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Biology 201 Chapter 7

The document outlines the process of cellular respiration which involves glycolysis, pyruvate oxidation, the Krebs cycle, and the electron transport chain. Glycolysis converts glucose to pyruvate, producing 2 ATP and 2 NADH. In the presence of oxygen, pyruvate is oxidized to acetyl-CoA which enters the Krebs cycle. The Krebs cycle further oxidizes acetyl-CoA, producing 3 more NADH, 1 FADH2, and 1 ATP by substrate-level phosphorylation. Electrons from NADH and FADH2 are used to build an electrochemical gradient through the electron transport chain which powers ATP synthesis through oxidative phosphorylation.

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Chapter 07 Lecture and Animation Outline See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes and animations. To run the animations you must be in Slideshow View. Use the buttons on the animation to play, pause, and turn audio/text on or off. Please Note: Once you have used any of the animation functions (such as Play or Pause), you must first click on the slide’s background before you can advance to the next slide.
2 Respiration • Organisms can be classified based on how they obtain energy: • Autotrophs – Able to produce their own organic molecules through photosynthesis • Heterotrophs – Live on organic compounds produced by other organisms • All organisms use cellular respiration to extract energy from organic molecules
3 Cellular respiration • Cellular respiration is a series of reactions • Oxidized – loss of electrons • Reduced – gain of electron • Dehydrogenation – lost electrons are accompanied by protons – A hydrogen atom is lost (1 electron, 1 proton)
4 Redox • During redox reactions, electrons carry energy from one molecule to another • Nicotinamide adenosine dinucleotide (NAD+) – An electron carrier – NAD+ accepts 2 electrons and 1 proton to become NADH – Reaction is reversible
5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Product Enzyme NAD+ NAD+ NAD NAD 2e– H+ +H+ Energy-rich molecule NAD+ 1. Enzymes that use NAD+ as a cofactor for oxidation reactions bind NAD+ and the substrate. 2. In an oxidation–reduction reaction, 2 electrons and a proton are transferred to NAD+ , forming NADH. A second proton is donated to the solution. 3. NADH diffuses away and can then donate electrons to other molecules. Reduction Oxidation H H H H H H H H
• In overall cellular energy harvest – Dozens of redox reactions take place – Number of electron acceptors including NAD+ • In the end, high-energy electrons from initial chemical bonds have lost much of their energy • Transferred to a final electron acceptor 6
7 • Aerobic respiration – Final electron receptor is oxygen (O2) • Anaerobic respiration – Final electron acceptor is an inorganic molecule (not O2) • Fermentation – Final electron acceptor is an organic molecule
8 Aerobic respiration C6H12O6 + 6O2 6CO2 + 6H2O Free energy = – 686 kcal/mol of glucose Free energy can be even higher than this in a cell • This large amount of energy must be released in small steps rather than all at once.
9 2e– Electrons from food High energy Low energy 2H+ 1/2O2 Energy released for ATP synthesis H2O Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Electron carriers • Many types of carriers used – Soluble, membrane-bound, move within membrane • All carriers can be easily oxidized and reduced • Some carry just electrons, some electrons and protons • NAD+ acquires 2 electrons and a proton to become NADH 10
11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H H O NH2 + 2H CH2O O O H H NH2 H H N N N CH2O O O H H NH2 O– H H N N N H H O N N H H H C C O P O PO– O P O– O P N N OH CH2 NADH: Reduced form of nicotinamide O O O O NAD+ : Oxidized form of nicotinamide Reduction Oxidation Adenine Adenine OH OH OH OHOH OHOH NH2 + H+ CH2 O–
12 ATP • Cells use ATP to drive endergonic reactions – ΔG (free energy) = –7.3 kcal/mol • 2 mechanisms for synthesis 1. Substrate-level phosphorylation • Transfer phosphate group directly to ADP • During glycolysis 2. Oxidative phosphorylation • ATP synthase uses energy from a proton gradient
13 PEP – ADP Enzyme Enzyme – ATP Adenosine Pyruvate P PP P P Adenosine P Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
14 Oxidation of Glucose The complete oxidation of glucose proceeds in stages: 1. Glycolysis 2. Pyruvate oxidation 3. Krebs cycle 4. Electron transport chain & chemiosmosis
15 Outer mitochondrial membrane Intermembrane space Mitochondrial matrix FAD O2 Inner mitochondrial membrane Electron Transport Chain Chemiosmosis ATP Synthase NAD+ Glycolysis Pyruvate Glucose Pyruvate Oxidation Acetyl-CoA Krebs Cycle CO2 ATPH2O ATP e– e– NADH NADH CO2 ATP NADH FADH2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H+ e–
16 Glycolysis • Converts 1 glucose (6 carbons) to 2 pyruvate (3 carbons) • 10-step biochemical pathway • Occurs in the cytoplasm • Net production of 2 ATP molecules by substrate-level phosphorylation • 2 NADH produced by the reduction of NAD+
17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis NADH Pyruvate Oxidation ATP Electron Transport Chain Chemiosmosis Krebs Cycle 6-carbon sugar diphosphate NAD+ NAD+ PrimingReactionsCleavageOxidationandATPFormation NADH NADH P P P P ATP ATP ADP ADP 3-carbon sugar phosphate 3-carbon sugar phosphate PiPi ADP ADP ATP ATP ATP ADP ADP ATP 3-carbon pyruvate 3-carbon pyruvate 6-carbon glucose (Starting material) Glycolysis begins with the addition of energy. Two high- energy phosphates (P) from two molecules of ATP are added to the 6-carbon molecule glucose, producing a 6-carbon molecule with two phosphates. Then, the 6-carbon molecule with two phosphates is split in two, forming two 3-carbon sugar phosphates. An additional Inorganic phosphate ( Pi ) is incorporated into each 3-carbon sugar phosphate. An oxidation reaction converts the two sugar phosphates into intermediates that can transfer a phosphate to ADP to form ATP. The oxidation reactions also yield NADH giving a net energy yield of 2 ATP and 2 NADH.
18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. NADH NAD+ NADH Pi NAD+ Glucose Hexokinase Phosphofructokinase Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate Isomerase Aldolase Pyruvate Pyruvate Enolase Pyruvate kinase ADP 10 Glucose Glyceraldehyde 3-phosphate Pyruvate Glycolysis: The ReactionsGlycolysis NADH Pyruvate Oxidation H2O ATP ADP Electron Transport Chain Chemiosmosis Krebs Cycle ATP ATP Phosphoglucose isomerase Glyceraldehyde 3- phosphate (G3P) Dihydroxyacetone phosphate 1. Phosphorylation of glucose by ATP. 2–3. Rearrangement, followed by a second ATP phosphorylation. 4–5. The 6-carbon molecule is split into two 3-carbon molecules—one G3P, another that is converted into G3P in another reaction. 6. Oxidation followed by phosphorylation produces two NADH molecules and two molecules of BPG, each with one high-energy phosphate bond. 7. Removal of high-energy phosphate by two ADP molecules produces two ATP molecules and leaves two 3PG molecules. 8–9. Removal of water yields two PEP molecules, each with a high-energy phosphate bond. 10. Removal of high-energy phosphate by two ADP molecules produces two ATP molecules and two pyruvate molecules. 1,3-Bisphosphoglycerate (BPG) 1,3-Bisphosphoglycerate (BPG) Glyceraldehyde 3-phosphate dehydrogenase Pi ADP Phosphoglycerate kinase ADP ATP 3-Phosphoglycerate (3PG) 3-Phosphoglycerate (3PG) 2-Phosphoglycerate (2PG) 2-Phosphoglycerate (2PG) H2O ATP Phosphoenolpyruvate (PEP) Phosphoenolpyruvate (PEP) ADP ADP ATP ATP Phosphoenol- pyruvate 3-Phospho- glycerate 1,3-Bisphospho- glycerate Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate Dihydroxyacetone Phosphate 2-Phospho- glycerate CH2OH O CH2 O O P CH2 O O P CH2OH O CH2 CH2 O O P P CHOH H C O CH2 O P C O O CH2P CH2OH CHOH O C O CH2 O P P CHOH O– C O CH2 O P H C O O– C O CH2OH P C O O– C O CH2 P C O O– C O CH3 8 9 10 7 4 5 3 2 1 6 Phosphoglyceromutase
19 Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
20 NADH must be recycled • For glycolysis to continue, NADH must be recycled to NAD+ by either: 1. Aerobic respiration – Oxygen is available as the final electron acceptor – Produces significant amount of ATP 2. Fermentation – Occurs when oxygen is not available – Organic molecule is the final electron acceptor
21 Fate of pyruvate • Depends on oxygen availability. – When oxygen is present, pyruvate is oxidized to acetyl-CoA which enters the Krebs cycle • Aerobic respiration – Without oxygen, pyruvate is reduced in order to oxidize NADH back to NAD+ • Fermentation
22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Without oxygen NAD+ O2 NADH ETC in mitochondria Acetyl-CoA Ethanol NAD+ CO2 NAD+ H2O Lactate Pyruvate AcetaldehydeNADH NADH With oxygen Krebs Cycle
23 Pyruvate Oxidation • In the presence of oxygen, pyruvate is oxidized – Occurs in the mitochondria in eukaryotes • multienzyme complex called pyruvate dehydrogenase catalyzes the reaction – Occurs at the plasma membrane in prokaryotes
24 • For each 3-carbon pyruvate molecule: – 1 CO2 • Decarboxylation by pyruvate dehydrogenase – 1 NADH – 1 acetyl-CoA which consists of 2 carbons from pyruvate attached to coenzyme A • Acetyl-CoA proceeds to the Krebs cycle Products of pyruvate oxidation
25 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis Pyruvate Oxidation NADH Krebs Cycle Electron Transport Chain Chemiosmosis Pyruvate Oxidation: The Reaction NAD+ CO2 CoA Acetyl Coenzyme A Pyruvate PyruvateAcetylCoenzymeA O CH 3 C O– C O  S CoA CH3 OC  NADH
26 Krebs Cycle • Oxidizes the acetyl group from pyruvate • Occurs in the matrix of the mitochondria • Biochemical pathway of 9 steps in three segments 1. Acetyl-CoA + oxaloacetate → citrate 2. Citrate rearrangement and decarboxylation 3. Regeneration of oxaloacetate
27 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CoA- (Acetyl-CoA) CoA 4-carbon molecule (oxaloacetate) 6-carbon molecule (citrate) NAD + NADH CO2 5-carbon molecule NAD+ NADH CO2 4-carbon molecule ADP + P Krebs Cycle FAD FADH2 4-carbon molecule NAD+ NADH ATP Glycolysis Pyruvate Oxidation Electron Transport Chain Chemiosmosis ATP 4-carbon molecule Pyruvate from glycolysis is oxidized Krebs Cycle into an acetyl group that feeds into the Krebs cycle. The 2-C acetyl group combines with 4-C oxaloacetate to produce the 6-C compound citrate (thus this is also called the citric acid cycle). Oxidation reactions are combined with two decarboxylations to produce NADH, CO2, and a new 4-carbon molecule. Two additional oxidations generate another NADH and an FADH2 and regenerate the original 4-C oxaloacetate. NADH FADH2 Krebs Cycle
28 Krebs Cycle • For each Acetyl-CoA entering: – Release 2 molecules of CO2 – Reduce 3 NAD+ to 3 NADH – Reduce 1 FAD (electron carrier) to FADH2 – Produce 1 ATP – Regenerate oxaloacetate
29 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis NADH FADH2 Pyruvate Oxidation ATP Krebs Cycle: The Reactions Citrate synthetase NAD+ NADH H2O NAD+ NADH CO2 Isocitrate dehydrogenase Fumarase CoA-SH 1 2 Aconitase 3 4 8 9 7 CoA-SH NAD+ CO2 5 6 NADH CoA-SH GDP + Pi Acetyl-CoA ═ CH3 — C— S O CoA — Krebs Cycle Malate dehydrogenase α-Ketoglutarate dehydrogenase Succinyl-CoA synthetase GTP ATP ADP Succinate dehydrogenase FADH2 8–9. Reactions 8 and 9: Regeneration of oxaloacetate and the fourth oxidation 7. Reaction 7: The third oxidation 6. Reaction 6: Substrate-level phosphorylation 5. Reaction 5: The second oxidation 4. Reaction 4: The first oxidation 2–3. Reactions 2 and 3: Isomerization 1. Reaction 1: Condensation Electron T ransport Chain Chemiosmosis Oxaloacetate (4C) CH2 O ═ C COO— COO— ——— Citrate (6C) HO—C—COO— COO— COO— CH2 CH2 ———— Isocitrate (6C) HC—COO— COO— COO— CH2 HO—CH ———— α-Ketoglutarate (5C) CH2 COO— COO— CH2 C—O ———— Succinyl-CoA (4C) CH2 COO— S—CoA CH2 C═ O ———— Succinate (4C) COO— CH2 COO— CH2 ——— Fumarate (4C) HC CH ═ COO— COO— —— Malate (4C) HO— CH COO— CH2 COO— ——— FAD
30 At this point • Glucose has been oxidized to: – 6 CO2 – 4 ATP – 10 NADH – 2 FADH2 • Electron transfer has released 53 kcal/mol of energy by gradual energy extraction • Energy will be put to use to manufacture ATP These electron carriers proceed to the electron transport chain
31 Electron Transport Chain (ETC) • ETC is a series of membrane-bound electron carriers • Embedded in the inner mitochondrial membrane • Electrons from NADH and FADH2 are transferred to complexes of the ETC • Each complex – A proton pump creating proton gradient – Transfers electrons to next carrier
32 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitochondrial matrix NADH + H+ ADP + Pi H2O H+ H+ 2H+ + 1/2O2 Glycolysis Pyruvate Oxidation 2 Krebs Cycle ATP Electron Transport Chain Chemiosmosis NADH dehydrogenase bc1 complex Cytochrome oxidase complex Inner mitochondrial membrane Intermembrane space a. The electron transport chain ATP synthase b. Chemiosmosis NAD+ Q C e– FADH2 H+ H+ H+ H+ e–22 e– 22 ATP FAD
33 Chemiosmosis • Accumulation of protons in the intermembrane space drives protons into the matrix via diffusion • Membrane relatively impermeable to ions • Most protons can only reenter matrix through ATP synthase – Uses energy of gradient to make ATP from ADP + Pi
34 ADP + Pi Catalytic head Stalk Rotor H+ H+ Mitochondrial matrix Intermembrane space H+ H+ H+ H+ H+ ATP Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
35 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H2O CO2 CO2 H+ H+ 2H+ + 1 /2O2 H+ e– H+ 32 ATP Krebs Cycle 2 ATP NADH NADH FADH2 NADH Pyruvate Oxidation Acetyl-CoA e– Q C e– Glycolysis Glucose Pyruvate
36 Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
37 Energy Yield of Respiration • Theoretical energy yield – 38 ATP per glucose for bacteria – 36 ATP per glucose for eukaryotes • Actual energy yield – 30 ATP per glucose for eukaryotes – Reduced yield is due to • “Leaky” inner membrane • Use of the proton gradient for purposes other than ATP synthesis
38 Chemiosmosis Chemiosmosis 2 5 2 3 6 15 2 2 2 5NADH NADH NADH Total net ATP yield = 32 (30 in eukaryotes) ATP ATP ATP ATP ATP ATP Krebs Cycle Pyruvate oxidation FADH2 Glycolysis2 Glucose Pyruvate ATP Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
39 Regulation of Respiration • Example of feedback inhibition • 2 key control points 1. In glycolysis • Phosphofructokinase is allosterically inhibited by ATP and/or citrate 2. In pyruvate oxidation • Pyruvate dehydrogenase inhibited by high levels of NADH • Citrate synthetase inhibited by high levels of ATP
40 Glucose Acetyl-CoA Fructose 6-phosphate Fructose 1,6-bisphosphate Pyruvate Pyruvate Oxidation Krebs Cycle Electron Transport Chain and Chemiosmosis Citrate ATP NADH Inhibits Inhibits Inhibits Phosphofructokinase Pyruvate dehydrogenase Glycolysis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ADP Activates
41 Oxidation Without O2 1. Anaerobic respiration – Use of inorganic molecules (other than O2) as final electron acceptor – Many prokaryotes use sulfur, nitrate, carbon dioxide or even inorganic metals 2. Fermentation – Use of organic molecules as final electron acceptor
42 Anaerobic respiration • Methanogens – CO2 is reduced to CH4 (methane) – Found in diverse organisms including cows • Sulfur bacteria – Inorganic sulphate (SO4) is reduced to hydrogen sulfide (H2S) – Early sulfate reducers set the stage for evolution of photosynthesis
43 a: © Wolfgang Baumeister/Photo Researchers, Inc.; b: NPS Photo Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b.a. 0.625 µm
44 Fermentation • Reduces organic molecules in order to regenerate NAD+ 1. Ethanol fermentation occurs in yeast – CO2, ethanol, and NAD+ are produced 2. Lactic acid fermentation – Occurs in animal cells (especially muscles) – Electrons are transferred from NADH to pyruvate to produce lactic acid
45 CO2 2 Acetaldehyde 2 ADP 2 Lactate Alcohol Fermentation in Yeast 2 ADP Lactic Acid Fermentation in Muscle Cells 2 NAD+ 2 NAD+ 2 NADH 2 NADH 2 ATP 2 ATP C O C O O– CH3 C O H CH3 C O C O CH3 O– CH3 H C OH C O O– H 2 Ethanol H C OH CH3 2 Pyruvate 2 Pyruvate Glucose Glucose G L Y C O L Y S I S G L Y C O L Y S I S Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
46 Catabolism of Protein • Amino acids undergo deamination to remove the amino group • Remainder of the amino acid is converted to a molecule that enters glycolysis or the Krebs cycle – Alanine is converted to pyruvate – Aspartate is converted to oxaloacetate
47 C HO O HO O C C HO O O C C O CH H CH H CH H CH H CH2N H NH3 HO Urea Glutamate α-Ketoglutarate Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
48 Catabolism of Fat • Fats are broken down to fatty acids and glycerol – Fatty acids are converted to acetyl groups by β-oxidation – Oxygen-dependent process • The respiration of a 6-carbon fatty acid yields 20% more energy than 6-carbon glucose.
49 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CoA Fatty acid OO —C —C —C — ═ H H — ═ — ATP NADH H2O Krebs Cycle PPiAMP + FADH2 Fatty acid 2C shorter CoA CoA Fatty acid OH H —C —C—C— —— H H — ═ — Fatty acid OH O H H —C —C— C ═ — —— H H —— CoA FAD Fatty acid OH —C ═ C —C — — H — ═ CoA Fatty acid OHO H —C —C —C — —— H H — ═ — CoA NAD+ Acetyl-CoA
50 Cell building blocks Deamination β-oxidation Glycolysis Oxidative respiration Ultimate metabolic products Acetyl-CoA Pyruvate Macromolecule degradation Krebs Cycle Nucleic acids Polysaccharides Nucleotides Amino acids Fatty acidsSugars Proteins Lipids and fats NH3 H2O CO2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
51 Evolution of Metabolism • Hypothetical timeline 1. Ability to store chemical energy in ATP 2. Evolution of glycolysis • Pathway found in all living organisms 3. Anaerobic photosynthesis (using H2S) 4. Use of H2O in photosynthesis (not H2S) • Begins permanent change in Earth’s atmosphere 5. Evolution of nitrogen fixation 6. Aerobic respiration evolved most recently

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Biology 201 Chapter 7

  • 1.
    Chapter 07 Lecture and AnimationOutline See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes and animations. To run the animations you must be in Slideshow View. Use the buttons on the animation to play, pause, and turn audio/text on or off. Please Note: Once you have used any of the animation functions (such as Play or Pause), you must first click on the slide’s background before you can advance to the next slide.
  • 2.
    2 Respiration • Organisms canbe classified based on how they obtain energy: • Autotrophs – Able to produce their own organic molecules through photosynthesis • Heterotrophs – Live on organic compounds produced by other organisms • All organisms use cellular respiration to extract energy from organic molecules
  • 3.
    3 Cellular respiration • Cellularrespiration is a series of reactions • Oxidized – loss of electrons • Reduced – gain of electron • Dehydrogenation – lost electrons are accompanied by protons – A hydrogen atom is lost (1 electron, 1 proton)
  • 4.
    4 Redox • During redoxreactions, electrons carry energy from one molecule to another • Nicotinamide adenosine dinucleotide (NAD+) – An electron carrier – NAD+ accepts 2 electrons and 1 proton to become NADH – Reaction is reversible
  • 5.
    5 Copyright © TheMcGraw-Hill Companies, Inc. Permission required for reproduction or display. Product Enzyme NAD+ NAD+ NAD NAD 2e– H+ +H+ Energy-rich molecule NAD+ 1. Enzymes that use NAD+ as a cofactor for oxidation reactions bind NAD+ and the substrate. 2. In an oxidation–reduction reaction, 2 electrons and a proton are transferred to NAD+ , forming NADH. A second proton is donated to the solution. 3. NADH diffuses away and can then donate electrons to other molecules. Reduction Oxidation H H H H H H H H
  • 6.
    • In overallcellular energy harvest – Dozens of redox reactions take place – Number of electron acceptors including NAD+ • In the end, high-energy electrons from initial chemical bonds have lost much of their energy • Transferred to a final electron acceptor 6
  • 7.
    7 • Aerobic respiration –Final electron receptor is oxygen (O2) • Anaerobic respiration – Final electron acceptor is an inorganic molecule (not O2) • Fermentation – Final electron acceptor is an organic molecule
  • 8.
    8 Aerobic respiration C6H12O6 +6O2 6CO2 + 6H2O Free energy = – 686 kcal/mol of glucose Free energy can be even higher than this in a cell • This large amount of energy must be released in small steps rather than all at once.
  • 9.
    9 2e– Electrons from food Highenergy Low energy 2H+ 1/2O2 Energy released for ATP synthesis H2O Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  • 10.
    Electron carriers • Manytypes of carriers used – Soluble, membrane-bound, move within membrane • All carriers can be easily oxidized and reduced • Some carry just electrons, some electrons and protons • NAD+ acquires 2 electrons and a proton to become NADH 10
  • 11.
    11 Copyright © TheMcGraw-Hill Companies, Inc. Permission required for reproduction or display. H H O NH2 + 2H CH2O O O H H NH2 H H N N N CH2O O O H H NH2 O– H H N N N H H O N N H H H C C O P O PO– O P O– O P N N OH CH2 NADH: Reduced form of nicotinamide O O O O NAD+ : Oxidized form of nicotinamide Reduction Oxidation Adenine Adenine OH OH OH OHOH OHOH NH2 + H+ CH2 O–
  • 12.
    12 ATP • Cells useATP to drive endergonic reactions – ΔG (free energy) = –7.3 kcal/mol • 2 mechanisms for synthesis 1. Substrate-level phosphorylation • Transfer phosphate group directly to ADP • During glycolysis 2. Oxidative phosphorylation • ATP synthase uses energy from a proton gradient
  • 13.
    13 PEP – ADP Enzyme Enzyme –ATP Adenosine Pyruvate P PP P P Adenosine P Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  • 14.
    14 Oxidation of Glucose Thecomplete oxidation of glucose proceeds in stages: 1. Glycolysis 2. Pyruvate oxidation 3. Krebs cycle 4. Electron transport chain & chemiosmosis
  • 15.
    15 Outer mitochondrial membrane Intermembrane space Mitochondrial matrix FAD O2 Inner mitochondrial membrane Electron Transport Chain Chemiosmosis ATPSynthase NAD+ Glycolysis Pyruvate Glucose Pyruvate Oxidation Acetyl-CoA Krebs Cycle CO2 ATPH2O ATP e– e– NADH NADH CO2 ATP NADH FADH2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H+ e–
  • 16.
    16 Glycolysis • Converts 1glucose (6 carbons) to 2 pyruvate (3 carbons) • 10-step biochemical pathway • Occurs in the cytoplasm • Net production of 2 ATP molecules by substrate-level phosphorylation • 2 NADH produced by the reduction of NAD+
  • 17.
    17 Copyright © TheMcGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis NADH Pyruvate Oxidation ATP Electron Transport Chain Chemiosmosis Krebs Cycle 6-carbon sugar diphosphate NAD+ NAD+ PrimingReactionsCleavageOxidationandATPFormation NADH NADH P P P P ATP ATP ADP ADP 3-carbon sugar phosphate 3-carbon sugar phosphate PiPi ADP ADP ATP ATP ATP ADP ADP ATP 3-carbon pyruvate 3-carbon pyruvate 6-carbon glucose (Starting material) Glycolysis begins with the addition of energy. Two high- energy phosphates (P) from two molecules of ATP are added to the 6-carbon molecule glucose, producing a 6-carbon molecule with two phosphates. Then, the 6-carbon molecule with two phosphates is split in two, forming two 3-carbon sugar phosphates. An additional Inorganic phosphate ( Pi ) is incorporated into each 3-carbon sugar phosphate. An oxidation reaction converts the two sugar phosphates into intermediates that can transfer a phosphate to ADP to form ATP. The oxidation reactions also yield NADH giving a net energy yield of 2 ATP and 2 NADH.
  • 18.
    18 Copyright © TheMcGraw-Hill Companies, Inc. Permission required for reproduction or display. NADH NAD+ NADH Pi NAD+ Glucose Hexokinase Phosphofructokinase Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate Isomerase Aldolase Pyruvate Pyruvate Enolase Pyruvate kinase ADP 10 Glucose Glyceraldehyde 3-phosphate Pyruvate Glycolysis: The ReactionsGlycolysis NADH Pyruvate Oxidation H2O ATP ADP Electron Transport Chain Chemiosmosis Krebs Cycle ATP ATP Phosphoglucose isomerase Glyceraldehyde 3- phosphate (G3P) Dihydroxyacetone phosphate 1. Phosphorylation of glucose by ATP. 2–3. Rearrangement, followed by a second ATP phosphorylation. 4–5. The 6-carbon molecule is split into two 3-carbon molecules—one G3P, another that is converted into G3P in another reaction. 6. Oxidation followed by phosphorylation produces two NADH molecules and two molecules of BPG, each with one high-energy phosphate bond. 7. Removal of high-energy phosphate by two ADP molecules produces two ATP molecules and leaves two 3PG molecules. 8–9. Removal of water yields two PEP molecules, each with a high-energy phosphate bond. 10. Removal of high-energy phosphate by two ADP molecules produces two ATP molecules and two pyruvate molecules. 1,3-Bisphosphoglycerate (BPG) 1,3-Bisphosphoglycerate (BPG) Glyceraldehyde 3-phosphate dehydrogenase Pi ADP Phosphoglycerate kinase ADP ATP 3-Phosphoglycerate (3PG) 3-Phosphoglycerate (3PG) 2-Phosphoglycerate (2PG) 2-Phosphoglycerate (2PG) H2O ATP Phosphoenolpyruvate (PEP) Phosphoenolpyruvate (PEP) ADP ADP ATP ATP Phosphoenol- pyruvate 3-Phospho- glycerate 1,3-Bisphospho- glycerate Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate Dihydroxyacetone Phosphate 2-Phospho- glycerate CH2OH O CH2 O O P CH2 O O P CH2OH O CH2 CH2 O O P P CHOH H C O CH2 O P C O O CH2P CH2OH CHOH O C O CH2 O P P CHOH O– C O CH2 O P H C O O– C O CH2OH P C O O– C O CH2 P C O O– C O CH3 8 9 10 7 4 5 3 2 1 6 Phosphoglyceromutase
  • 19.
    19 Please note thatdue to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • 20.
    20 NADH must berecycled • For glycolysis to continue, NADH must be recycled to NAD+ by either: 1. Aerobic respiration – Oxygen is available as the final electron acceptor – Produces significant amount of ATP 2. Fermentation – Occurs when oxygen is not available – Organic molecule is the final electron acceptor
  • 21.
    21 Fate of pyruvate •Depends on oxygen availability. – When oxygen is present, pyruvate is oxidized to acetyl-CoA which enters the Krebs cycle • Aerobic respiration – Without oxygen, pyruvate is reduced in order to oxidize NADH back to NAD+ • Fermentation
  • 22.
    22 Copyright © TheMcGraw-Hill Companies, Inc. Permission required for reproduction or display. Without oxygen NAD+ O2 NADH ETC in mitochondria Acetyl-CoA Ethanol NAD+ CO2 NAD+ H2O Lactate Pyruvate AcetaldehydeNADH NADH With oxygen Krebs Cycle
  • 23.
    23 Pyruvate Oxidation • Inthe presence of oxygen, pyruvate is oxidized – Occurs in the mitochondria in eukaryotes • multienzyme complex called pyruvate dehydrogenase catalyzes the reaction – Occurs at the plasma membrane in prokaryotes
  • 24.
    24 • For each3-carbon pyruvate molecule: – 1 CO2 • Decarboxylation by pyruvate dehydrogenase – 1 NADH – 1 acetyl-CoA which consists of 2 carbons from pyruvate attached to coenzyme A • Acetyl-CoA proceeds to the Krebs cycle Products of pyruvate oxidation
  • 25.
    25 Copyright © TheMcGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis Pyruvate Oxidation NADH Krebs Cycle Electron Transport Chain Chemiosmosis Pyruvate Oxidation: The Reaction NAD+ CO2 CoA Acetyl Coenzyme A Pyruvate PyruvateAcetylCoenzymeA O CH 3 C O– C O  S CoA CH3 OC  NADH
  • 26.
    26 Krebs Cycle • Oxidizesthe acetyl group from pyruvate • Occurs in the matrix of the mitochondria • Biochemical pathway of 9 steps in three segments 1. Acetyl-CoA + oxaloacetate → citrate 2. Citrate rearrangement and decarboxylation 3. Regeneration of oxaloacetate
  • 27.
    27 Copyright © TheMcGraw-Hill Companies, Inc. Permission required for reproduction or display. CoA- (Acetyl-CoA) CoA 4-carbon molecule (oxaloacetate) 6-carbon molecule (citrate) NAD + NADH CO2 5-carbon molecule NAD+ NADH CO2 4-carbon molecule ADP + P Krebs Cycle FAD FADH2 4-carbon molecule NAD+ NADH ATP Glycolysis Pyruvate Oxidation Electron Transport Chain Chemiosmosis ATP 4-carbon molecule Pyruvate from glycolysis is oxidized Krebs Cycle into an acetyl group that feeds into the Krebs cycle. The 2-C acetyl group combines with 4-C oxaloacetate to produce the 6-C compound citrate (thus this is also called the citric acid cycle). Oxidation reactions are combined with two decarboxylations to produce NADH, CO2, and a new 4-carbon molecule. Two additional oxidations generate another NADH and an FADH2 and regenerate the original 4-C oxaloacetate. NADH FADH2 Krebs Cycle
  • 28.
    28 Krebs Cycle • Foreach Acetyl-CoA entering: – Release 2 molecules of CO2 – Reduce 3 NAD+ to 3 NADH – Reduce 1 FAD (electron carrier) to FADH2 – Produce 1 ATP – Regenerate oxaloacetate
  • 29.
    29 Copyright © TheMcGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis NADH FADH2 Pyruvate Oxidation ATP Krebs Cycle: The Reactions Citrate synthetase NAD+ NADH H2O NAD+ NADH CO2 Isocitrate dehydrogenase Fumarase CoA-SH 1 2 Aconitase 3 4 8 9 7 CoA-SH NAD+ CO2 5 6 NADH CoA-SH GDP + Pi Acetyl-CoA ═ CH3 — C— S O CoA — Krebs Cycle Malate dehydrogenase α-Ketoglutarate dehydrogenase Succinyl-CoA synthetase GTP ATP ADP Succinate dehydrogenase FADH2 8–9. Reactions 8 and 9: Regeneration of oxaloacetate and the fourth oxidation 7. Reaction 7: The third oxidation 6. Reaction 6: Substrate-level phosphorylation 5. Reaction 5: The second oxidation 4. Reaction 4: The first oxidation 2–3. Reactions 2 and 3: Isomerization 1. Reaction 1: Condensation Electron T ransport Chain Chemiosmosis Oxaloacetate (4C) CH2 O ═ C COO— COO— ——— Citrate (6C) HO—C—COO— COO— COO— CH2 CH2 ———— Isocitrate (6C) HC—COO— COO— COO— CH2 HO—CH ———— α-Ketoglutarate (5C) CH2 COO— COO— CH2 C—O ———— Succinyl-CoA (4C) CH2 COO— S—CoA CH2 C═ O ———— Succinate (4C) COO— CH2 COO— CH2 ——— Fumarate (4C) HC CH ═ COO— COO— —— Malate (4C) HO— CH COO— CH2 COO— ——— FAD
  • 30.
    30 At this point •Glucose has been oxidized to: – 6 CO2 – 4 ATP – 10 NADH – 2 FADH2 • Electron transfer has released 53 kcal/mol of energy by gradual energy extraction • Energy will be put to use to manufacture ATP These electron carriers proceed to the electron transport chain
  • 31.
    31 Electron Transport Chain(ETC) • ETC is a series of membrane-bound electron carriers • Embedded in the inner mitochondrial membrane • Electrons from NADH and FADH2 are transferred to complexes of the ETC • Each complex – A proton pump creating proton gradient – Transfers electrons to next carrier
  • 32.
    32 Copyright © TheMcGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitochondrial matrix NADH + H+ ADP + Pi H2O H+ H+ 2H+ + 1/2O2 Glycolysis Pyruvate Oxidation 2 Krebs Cycle ATP Electron Transport Chain Chemiosmosis NADH dehydrogenase bc1 complex Cytochrome oxidase complex Inner mitochondrial membrane Intermembrane space a. The electron transport chain ATP synthase b. Chemiosmosis NAD+ Q C e– FADH2 H+ H+ H+ H+ e–22 e– 22 ATP FAD
  • 33.
    33 Chemiosmosis • Accumulation ofprotons in the intermembrane space drives protons into the matrix via diffusion • Membrane relatively impermeable to ions • Most protons can only reenter matrix through ATP synthase – Uses energy of gradient to make ATP from ADP + Pi
  • 34.
    34 ADP + Pi Catalytichead Stalk Rotor H+ H+ Mitochondrial matrix Intermembrane space H+ H+ H+ H+ H+ ATP Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  • 35.
    35 Copyright © TheMcGraw-Hill Companies, Inc. Permission required for reproduction or display. H2O CO2 CO2 H+ H+ 2H+ + 1 /2O2 H+ e– H+ 32 ATP Krebs Cycle 2 ATP NADH NADH FADH2 NADH Pyruvate Oxidation Acetyl-CoA e– Q C e– Glycolysis Glucose Pyruvate
  • 36.
    36 Please note thatdue to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • 37.
    37 Energy Yield ofRespiration • Theoretical energy yield – 38 ATP per glucose for bacteria – 36 ATP per glucose for eukaryotes • Actual energy yield – 30 ATP per glucose for eukaryotes – Reduced yield is due to • “Leaky” inner membrane • Use of the proton gradient for purposes other than ATP synthesis
  • 38.
    38 Chemiosmosis Chemiosmosis 2 5 2 3 615 2 2 2 5NADH NADH NADH Total net ATP yield = 32 (30 in eukaryotes) ATP ATP ATP ATP ATP ATP Krebs Cycle Pyruvate oxidation FADH2 Glycolysis2 Glucose Pyruvate ATP Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  • 39.
    39 Regulation of Respiration •Example of feedback inhibition • 2 key control points 1. In glycolysis • Phosphofructokinase is allosterically inhibited by ATP and/or citrate 2. In pyruvate oxidation • Pyruvate dehydrogenase inhibited by high levels of NADH • Citrate synthetase inhibited by high levels of ATP
  • 40.
    40 Glucose Acetyl-CoA Fructose 6-phosphate Fructose 1,6-bisphosphate Pyruvate PyruvateOxidation Krebs Cycle Electron Transport Chain and Chemiosmosis Citrate ATP NADH Inhibits Inhibits Inhibits Phosphofructokinase Pyruvate dehydrogenase Glycolysis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ADP Activates
  • 41.
    41 Oxidation Without O2 1.Anaerobic respiration – Use of inorganic molecules (other than O2) as final electron acceptor – Many prokaryotes use sulfur, nitrate, carbon dioxide or even inorganic metals 2. Fermentation – Use of organic molecules as final electron acceptor
  • 42.
    42 Anaerobic respiration • Methanogens –CO2 is reduced to CH4 (methane) – Found in diverse organisms including cows • Sulfur bacteria – Inorganic sulphate (SO4) is reduced to hydrogen sulfide (H2S) – Early sulfate reducers set the stage for evolution of photosynthesis
  • 43.
    43 a: © WolfgangBaumeister/Photo Researchers, Inc.; b: NPS Photo Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b.a. 0.625 µm
  • 44.
    44 Fermentation • Reduces organicmolecules in order to regenerate NAD+ 1. Ethanol fermentation occurs in yeast – CO2, ethanol, and NAD+ are produced 2. Lactic acid fermentation – Occurs in animal cells (especially muscles) – Electrons are transferred from NADH to pyruvate to produce lactic acid
  • 45.
    45 CO2 2 Acetaldehyde 2 ADP 2Lactate Alcohol Fermentation in Yeast 2 ADP Lactic Acid Fermentation in Muscle Cells 2 NAD+ 2 NAD+ 2 NADH 2 NADH 2 ATP 2 ATP C O C O O– CH3 C O H CH3 C O C O CH3 O– CH3 H C OH C O O– H 2 Ethanol H C OH CH3 2 Pyruvate 2 Pyruvate Glucose Glucose G L Y C O L Y S I S G L Y C O L Y S I S Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  • 46.
    46 Catabolism of Protein •Amino acids undergo deamination to remove the amino group • Remainder of the amino acid is converted to a molecule that enters glycolysis or the Krebs cycle – Alanine is converted to pyruvate – Aspartate is converted to oxaloacetate
  • 47.
    47 C HO O HO O C C HOO O C C O CH H CH H CH H CH H CH2N H NH3 HO Urea Glutamate α-Ketoglutarate Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  • 48.
    48 Catabolism of Fat •Fats are broken down to fatty acids and glycerol – Fatty acids are converted to acetyl groups by β-oxidation – Oxygen-dependent process • The respiration of a 6-carbon fatty acid yields 20% more energy than 6-carbon glucose.
  • 49.
    49 Copyright © TheMcGraw-Hill Companies, Inc. Permission required for reproduction or display. CoA Fatty acid OO —C —C —C — ═ H H — ═ — ATP NADH H2O Krebs Cycle PPiAMP + FADH2 Fatty acid 2C shorter CoA CoA Fatty acid OH H —C —C—C— —— H H — ═ — Fatty acid OH O H H —C —C— C ═ — —— H H —— CoA FAD Fatty acid OH —C ═ C —C — — H — ═ CoA Fatty acid OHO H —C —C —C — —— H H — ═ — CoA NAD+ Acetyl-CoA
  • 50.
    50 Cell building blocks Deaminationβ-oxidation Glycolysis Oxidative respiration Ultimate metabolic products Acetyl-CoA Pyruvate Macromolecule degradation Krebs Cycle Nucleic acids Polysaccharides Nucleotides Amino acids Fatty acidsSugars Proteins Lipids and fats NH3 H2O CO2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  • 51.
    51 Evolution of Metabolism •Hypothetical timeline 1. Ability to store chemical energy in ATP 2. Evolution of glycolysis • Pathway found in all living organisms 3. Anaerobic photosynthesis (using H2S) 4. Use of H2O in photosynthesis (not H2S) • Begins permanent change in Earth’s atmosphere 5. Evolution of nitrogen fixation 6. Aerobic respiration evolved most recently