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Download Class22 2-9 Win17 Respiration Regulation and
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Hans Krebs: Citric acid, and opportunities lost and gained Thursday February 9th, 2017 Class 22 Learning Goals Respiration: Regulation and Fermentation • After this class, you should be able to: • Classify a microorganism as eukaryotic or prokaryotic based on respiration details • Critically assess the usefulness of a particular regulation mechanism or feedback loop for a respiring organism or cell • Describe several different respiration schemes that are not aerobic respiration (and note environments in which these schemes might be most favored) • Identify a fermentation reaction and compare the energetic output with a similar aerobic reaction Peer Instruction Where are these found in the fake cells shown here? • Electron Transport Chain • Krebs Cycle • Linking Step • Glycolysis Fake Animal Cell Fake Plant Cell Peer Instruction Diagram how the overall scheme of respiration works in this prokaryote. Include: • Electron Transport Chain • Krebs Cycle • Linking Step • Glycolysis Clicker Question #1 The most efficient metabolism would make the greatest number of ATP per glucose molecule. Which type of cell has a more efficient metabolism? Why? 1) Eukaryotic --> it is bigger 2) Prokaryotic --> it is smaller 3) Eukaryotic --> more organelles to help with complex reactions 4) Prokaryotic --> no need to transport molecules through organelle membranes 5) They are equally efficient Peer Instruction Why is this negative feedback loop a good idea for the cell? How can the product molecule regulate an enzyme? Why are positive feedback loops rare in biology? Clicker Question #2 Examples of positive feedback are relatively rare in biological regulation. Why is this? 1) Positive feedback does not equilibrate response to a particular appropriate cellular level 2) Positive feedback requires more regulatory molecules 3) Positive feedback is not possible in cellular environments 4) Positive feedback can quickly become costly Explain how “feedback inhibition” works with this enzyme. Peer Instruction When ATP binds here, the reaction rate slows dramatically Fructose-1,6- bisphosphate at active site (as the reaction is completed) ADP at active site Peer Instruction This step is regulated by ATP These steps are also regulated via feedback inhibition, by ATP and NADH Citrate Acetyl CoA Oxaloacetate Does it make sense for the cell to use feedback inhibition here? Peer Instruction Why can a mutation that allows an additional input pathway improve the relative fitness of an organism? Peer Instruction Pathway for synthesis of RNA, DNA Fats Phospholipids Fatty acids Glycogen or starch Glucose Pyruvate Acetyl CoA GLYCOLYSIS KREBS CYCLE Lactate (from fermentation) How does diversification of metabolic output improve fitness for an organism? Several intermediates used as substrates in amino acid synthesis Metabolism: Full complexity Peer Instruction ‘Anaerobic’ means ‘without oxygen’. What do anaerobic respirators do differently in metabolism? Are C-C and C-H the only bonds that contain energy? What molecules are broken down by chemolithotrophs? Is ATP synthase the only ATP source in human respiration? Fermentation pathway: Fermentation by-product Peer Instruction Intermediate accepts electrons from NADH Explain how fermentation works. How does the ATP yield of fermentation compared to that of aerobic respiration? In what conditions would the evolution of enzymes and regulation to allow fermentation be advantageous? Peer Instruction Fermentation pathways: Allowing cells to make ATP and regenerate NAD+ without oxygen Fermentation by-product Intermediate accepts electrons from NADH Lactic acid fermentation occurs in humans. No intermediate; pyruvate accepts electrons from NADH 2 Pyruvate 2 Lactate Peer Instruction Fermentation pathways: Allowing cells to make ATP and regenerate NAD+ without oxygen Fermentation by-product Intermediate accepts electrons from NADH Alcohol fermentation occurs in yeast. 2 Ethanol 2 Pyruvate Concept Questions • Is this most likely prokaryotic or eukaryotic? How do you know? – A cell that is more basic than its environment – A cell that spends extra ATP to build membrane channels – A cell that concentrates ATP synthase in compartments of membrane • Which of these regulation methods would be most useful? Why? – Glucose makes 3 of the glycolysis enzymes work more slowly – ATP slows the linking step – Complex II prevents the formation of more mitochondria • What respiration scheme might work better than aerobic: – In a peat bog? – In outer space? – In the midst of a coral reef? • Imagine a species that metabolizes fructose down to methanol, and then feeds that methanol into their version of the Krebs’ cycle. Draw a reaction that would allow fermentation in this species. You can use the given diagrams for ethanol fermantation as a guide. – What does this species produce as a final product? How does it smell? – Does this species make a lot of ATP compared to its own aerobic pathway? • Metabolism: In Review Key Concepts – Glycolysis: Glucose is processed to pyruvate through the glycolysis reactions in the cytoplasm – Linking Step: Pyruvate is transferred into the mitochondria and transformed into the ‘sticky’ 2-carbon Acetyl-CoA – Krebs Cycle: Acetyl-CoA feeds the Krebs cycle, which uses the oxidation of carbohydrates to form reducing power (as NADH, FADH2) – Electron Transport Chain: High-energy electrons are driven through membrane proteins that pump protons to produce a gradient, with oxygen acting as the final electron acceptor in most organisms – Oxidative Phosphorylation: ATP synthase uses gradient energy to catalyze the formation of the energy currency of the cell, ATP – Regulation • • • • • Fermentation Alternative pathways Non-aerobic respiration mechanisms Differences in prokaryotes and eukaryotes Enzyme feedback inhibition Clicker Question #3 Carbon dioxide cannot be removed from the mitochondria, which process is likely to shut down first? 1. 2. 3. 4. Glycolysis the Linking Step the Electron Transport Chain the Krebs Cycle Clicker Question #4 You are a single-celled organism with a full set of respiration enzymes and essential precursor molecules. You are given your choice: You can have 20 of one of the following molecules….which would you rather have to maximize your ATP production? 1. NADH 2. A proton (moved from your cytoplasm outside your cell) 3. GTP 4. Acetyl-CoA 5. FAD+ 6. There are two equal best options Clicker Question #5 Prokaryote v. Eukaryote: NADH is an extremely large and polar molecule. Each NADH is worth roughly 2.4 ATP. In eukaryotes, several NADH molecules are made in the cytoplasm, but the electron transport chain is processed in the mitochondria. The mitochondria typically has a high concentration of NADH. So what? 1) This will lower the yield of ATP per glucose in prokaryotes 2) This will raise the yield of ATP per glucose in eukaryotes 3) Both eukaryotes and prokaryotes will make the same amount of ATP per glucose Clicker Question #6 You want to genetically engineer a prokaryote to have a stronger metabolism (in other words, to produce more ATP per glucose). There are many parts of the system that you could try to reengineer. Which one, if successful, might give you the best impact? 1. 2. 3. 4. 5. Create a ‘trapping step’ enzyme that does not cost 1 ATP Allow Complex II to pump a proton across the lipid membrane in the ETC Change ATP synthase to produce twice as many ATP with the same gradient Alter Krebs cycle intermediates to produce ATP instead of GTP Make the linking step work more efficiently