Cellular Respiration - Chapter 7 PDF

CELLULAR RESPIRATION Chapter 7 For one molecule of glucose, what is the maximum number of ATP molecules created directly from the Krebs cycle? A. 1 92% B. 2 C. 3 D. 4 4% 4%...

CELLULAR RESPIRATION Chapter 7 For one molecule of glucose, what is the maximum number of ATP molecules created directly from the Krebs cycle? A. 1 92% B. 2 C. 3 D. 4 4% 4% 0% 1 2 3 4 What is the name of the mechanism by which pyruvate dehydrogenase is inhibited by the end-product of the biochemical pathway? A. Anabolism 51% B. Catabolism C. Negative inhibition D. Regulation 20% 17% 13% m m n n lis lis tio tio o bo bi la ab ta hi gu An Ca in Re tive ga Ne Because it has 6 carbons, glucose can power 6 cycles ("turns") of the Krebs cycle A. True B. False  5 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  6 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)  7 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  8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Oxidation Energy-rich molecule Reduction Product Enzyme H H +H+ H H 2e– H H H+ H H NAD+ NAD+ NAD NAD NAD+ 1. Enzymes that use NAD+ 2. In an oxidation–reduction 3. NADH diffuses away as a cofactor for oxidation reaction, 2 electrons and and can then donate reactions bind NAD+ and the a proton are transferred electrons to other substrate. to NAD+, forming NADH. molecules. A second proton is donated to the solution.  9 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  10 Aerobic respiration Final electron receptor is oxygen (O ) 2 Anaerobic respiration Final electron acceptor is an inorganic molecule (not O2) Fermentation Final electron acceptor is an organic molecule  11 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.  12 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  13 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  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  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Outer 15 Glycolysis mitochondrial membrane Glucose Intermembrane space NADH ATP Pyruvate Pyruvate Oxidation Mitochondrial matrix NADH Acetyl-CoA CO2 NADH CO2 Krebs Cycle FADH2 ATP Inner mitochondrial e– membrane NAD+ FAD O2 H2O ATP e– Electron e– Chemiosmosis Transport Chain ATP Synthase H+  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+  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis ATP Glycolysis: The Reactions CH2OH Glucose O NADH Glucose Pyruvate Oxidation ATP 6-phosphate CH2 O P Hexokinase Glucose Krebs ADP O Cycle Glucose 6-phosphate Phosphoglucose Electron Transport Chain isomerase CH2 O P 1,6-bisphosphate 6-phosphate Chemiosmosis Fructose O CH2OH Fructose 6-phosphate ATP Phosphofructokinase 1. Phosphorylation of ADP P O CH2 CH2 O P Fructose glucose by ATP. O Fructose 1,6-bisphosphate 2–3. Rearrangement, followed by a second Aldolase ATP phosphorylation. Isomerase 1,3-Bisphospho- Dihydroxyacetone Glyceraldehyde 4–5. The 6-carbon molecule P O CH2 H Dihydroxyacetone Glyceraldehyde 3- 3-phosphate is split into two 3-carbon phosphate phosphate (G3P) C O C O molecules—one G3P, Phosphate another that is converted CH2OH CHOH into G3P in another reaction. NAD+ NAD+ CH2 O P Pi Pi 6. Oxidation followed by NADH Glyceraldehyde NADH phosphorylation produces 3-phosphate P O C O glycerate two NADH molecules and dehydrogenase two molecules of BPG, 1,3-Bisphosphoglycerate CHOH 1,3-Bisphosphoglycerate each with one (BPG) P (BPG) CH2 O high-energy phosphate bond. ADP ADP O– 3-Phospho- 7. Removal of high-energy ATP Phosphoglycerate ATP glycerate kinase C O phosphate by two ADP molecules produces two CHOH ATP molecules and leaves 3-Phosphoglycerate 3-Phosphoglycerate two 3PG molecules. (3PG) (3PG) CH2 O P 8–9. Removal of water yields two PEP molecules, each O– 2-Phospho- Phosphoglyceromutase glycerate with a high-energy C O phosphate bond. H C O P 10. Removal of high-energy 2-Phosphoglycerate 2-Phosphoglycerate phosphate by two ADP (2PG) (2PG) CH2OH molecules produces two ATP molecules and two O– Phosphoenol- pyruvate molecules. H2O H2O pyruvate Enolase C O C O P Phosphoenolpyruvate Phosphoenolpyruvate (PEP) (PEP) CH2 O– ADP 10 ADP C O Pyruvate ATP Pyruvate kinase ATP C O Pyruvate Pyruvate CH3  18 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  19 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  20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Without oxygen Pyruvate With oxygen H2O NAD + CO2 O2 NADH NADH Acetaldehyde ETC in mitochondria Acetyl-CoA NAD+ NADH NAD+ Lactate Krebs Cycle Ethanol  21 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  22 Products of pyruvate oxidation For each 3-carbon pyruvate molecule: 1 CO 2 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  23 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  24 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis Pyruvate Oxidation CoA- (Acetyl-CoA) CoA NADH Krebs 4-carbon ATP Cycle molecule FADH2 (oxaloacetate) 6-carbon molecule Electron Transport Chain NADH (citrate) Chemiosmosis NAD + NADH NAD+ CO2 Pyruvate from glycolysis is 4-carbon Krebs Cycle oxidized Krebs Cycle into an molecule 5-carbon acetyl group that feeds into the molecule Krebs cycle. The 2-C acetyl group combines with 4-C oxaloacetate to NAD+ produce the 6-C compound citrate FADH2 (thus this is also called the citric acid cycle). Oxidation reactions are combined with two NADH decarboxylations to produce FAD NADH, CO2, and a new 4-carbon molecule. Two additional CO2 oxidations generate another 4-carbon 4-carbon NADH and an FADH2 and molecule molecule regenerate the original 4-C oxaloacetate. ATP ADP + P  25 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  26 At this point Glucose has been oxidized to: 6 CO2 4 ATP 10 NADH These electron carriers proceed 2 FADH2 to the electron transport chain Electron transfer has released 53 kcal/mol of energy by gradual energy extraction Energy will be put to use to manufacture ATP  27 Electron Transport Chain (ETC) ETC is a series of membrane-bound electron carriers Embedded in the inner mitochondrial membrane Electrons from NADH and FADH are transferred to 2 complexes of the ETC Each complex A proton pump creating proton gradient Transfers electrons to next carrier  28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis Pyruvate Oxidation Krebs Cycle ATP Electron Transport Chain Chemiosmosis H++ ATP Mitochondrial matrix Cytochrome ATP NADH dehydrogenase bc1 complex oxidase complex synthase ADP + Pi NADH + H+ NAD+ 2H+ + 1/2O2 H2O FADH2 2 e– FAD 22 e– 22 e– Q C Inner mitochondrial membrane H+ H+ H+ H+ Intermembrane space a. The electron transport chain b. Chemiosmosis  29 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  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 30 H+ Mitochondrial matrix ATP ADP + Pi Catalytic head Stalk Rotor Intermembrane H+ H+ H + H+ space H+ H +  31 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis NADH Glucose Pyruvate NADH Pyruvate Oxidation CO2 Acetyl-CoA NADH CO2 H+ Krebs e– Cycle 32 ATP FADH2 2 ATP e– 2H+ H2O + 1/ O 2 2 e– Q C H+ H+ H+  32 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  33 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glucose 2 ATP 2 ATP Glycolysis Pyruvate 2 NADH 5 ATP Chemiosmosis Pyruvate oxidation 2 NADH 5 ATP 2 ATP Krebs Cycle 6 NADH 15 ATP Chemiosmosis 2 FADH2 3 ATP Total net ATP yield = 32 (30 in eukaryotes)  34 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  35 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  36 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  37 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  38 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  39 Catabolism of Fat Fats are broken down to fatty acids and glycerol Fatty acids are converted to acetyl groups by b-oxidation Oxygen-dependent process The respiration of a 6- carbon fatty acid yields 20% more energy than 6-carbon glucose.  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 40 Macromolecule degradation Nucleic acids Proteins Polysaccharides Lipids and fats Cell building blocks Nucleotides Amino acids Sugars Fatty acids Glycolysis Deamination -oxidation Oxidative respiration Pyruvate Acetyl-CoA Krebs Cycle Ultimate metabolic products NH3 H2O CO2  41 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 For one molecule of glucose, what is the maximum number of ATP molecules created directly from the Krebs cycle? A. 1 B. 2 C. 3 D. 4 What is the name of the mechanism by which pyruvate dehydrogenase is inhibited by the end-product of the biochemical pathway? A. Anabolism B. Catabolism C. Negative inhibition D. Regulation Because it has 6 carbons, glucose can power 6 cycles ("turns") of the Krebs cycle A. True B. False