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Transcript
Chapter 9 Cellular Respiration-ANSWERS 9.1 Catabolic pathways oxidize organic fuels____________________________________ 1.Where does the energy stored in organic molecules originally come from? Sun 2. Describe the flow of energy through an ecosystem. Starting with The energy souce you identified in the previous question. Sun Light energy autotrophs make glucose=chemical energy) herbivores use glucose to make ATP=another chemical energy when organisms use chemical energy some energy is always lost as Heat Energy during the transformation. 3. Write the equation for the catabolism (breakdown) of glucose. A. What are the Reactants? B. What are the Products? C. Is the reaction exergonic or endergonic? A. Reactants glucose and oxygen B. Products carbon dioxide and water C. Exergonic because energy is released when hydrogen atoms are removed from glucose by the dehydrogenase enzyme. 4. In a redox reaction, the loss of electrons from one substance is called (oxidation or reduction), and the addition of electrons to another substance is called (oxidation or reduction). Remember…LEO (Lose Electrons Oxidation) the tiger says GER (Gain Electrons Reduction) 5. Which reactant is oxidized and which is reduced in the equation for catabolisim (breakdown) of glucose? Electrons are taken away from glucose, so glucose is oxidized. Electrons are added to Oxygen in the last step of cell respiration, so it is reduced. 6. During Cellular respiration, glucose is not catabolized (broken down) in a single step. WHY? So that the energy stored in the bonds of glucose can be harnessed to make ATP. If all electrons were transferred to oxygen in one step very little energy would be captured to make ATP. 7. A.. What enzyme pulls the hydrogen atoms from glucose and transfers them to the coenzyme? Dehydrogenase B. To what coenzyme are the hydrogen atoms ( a hydrogen atom is made of 1electron and 1proton) transferred after being stripped from glucose? NAD+ C. How many electron(s) and proton(s) does this enzyme transfer to the coenzyme identified in the previous question? Two electrons, One proton D. After the enzyme transfers the appropriate number of electrons and protons to the coenzyme the coenzyme becomes NADH. Explain this transformation in terms of the number of electrons and protons transferred. Coenzyme NAD+ NADH -If we add 1 electron to NAD+ we get NAD. The electron has a negative charge, so it neutralizes the positive charge on NAD+ -To convert NAD to NADH, we need to add a hydrogen atom (H). A hydrogen atom is made of 1 electron and 1 proton. -In summary we have added 1 electron to convert NAD+ to NAD and 1 more electron and one proton to convert NAD to NADH! E. Using your answers for the previous questions A-D, explain why NADH is called an “electron carrier”. NADH will carry electrons pulled from glucose to the final step of cell respiration where their energy will be used to power the production of ATP. 9.2 Glycolysis____________________________________________________________ 8. Where does glycolysis occur? In the cytpplasm of the cell. 9. The word gylcolysis means “splitting sugar.” A) What sugar is split? Glucose B) What is this sugar split into (i.e. the end products of glycolysis?) 2 pyruvate molecules 10A.Why is the first part of glycolysis called the energy investment phase? 2 molecules of ATP are USED to complete the first half of the glycolysis reactions. 10B.Why is the second part of glycolysis called the energy payoff phase? 4 molecules of ATP are MADE to complete the other half of the glycolysis reactions. 10C. How many NET ATP are produced during one round of glycolysis? Net 2ATP are produced. You used 2 ATP in the energy investment. Then you made 4 ATP in the energy payoff phase, so you have an overall total (net) of 2 ATP at the end of glycolysis. 11.List the major products of glycolysis. Pyruvate ATP NADH 12. Of the products listed in the previous question, which is the most important product produced? EXPLAIN why it is the most important. Pyruvate. Pyruvate it is the major reactant for the next stage of cell respiration, the Krebs cycle/citric acid cycle. Without pyruvate the krebs/citric acid cycle will have no starting material and will not produce product. Without the major product of the citric acid cycle, the third and final step of cell respiration (where NEARLY ALL the ATP is made) will have not have enough stating material to produce its major product (ATP). 9.3 Krebs/Citric Acid Cycle (CAC)__________________________________________ 13. Where does the Krebs/Citric acid cycle occur? In the matrix (innermost space) of mitochondria. 14. Identify the major reactant for the Krebs/Citric Acid Cycle. Pyruvate (made in glycolysis) This is more info thatn you need to know for this course but just so you know…. …Pyruvate loses CO2 before entering the mitochondrial matrix and is converted into Acetyl CoA, which initiates the citric acid cycle. So Acetyl CoA is the actual starting material for the CAC, but it cannot be made without pyruvate, so this is why we say pyruvate is the major reactant 15. List the major products of the CAC. CO2 (this is the gas you exhale! It also happens to be one of the major reactants for photosynthesis!) ATP (just a little bit) NADH FADH2 16. Of the products listed in the previous question, which is the most important product produced? EXPLAIN why it is the most important. NADH/FADH2 NADH/FADH2 are the major reactants for the next stage of cell respiration, oxidative phsophorylation. Without NADH2 will have no starting material and will not produce product. Without the major product of the citric acid cycle, the third and final step of cell respiration (where NEARLY ALL the ATP is made) will have not have enough stating material to produce its major product (ATP). 17. Where are the NADH molecules that are produced in the CAC eventually used? Electron transport chain (ETC) during Oxidative Phosphorylation. They give the electrons they are carrying (that originally came from the bonds of glucose) to the protein pumps of the ETC. The electrons give the protein pumps energy to pump ions across the innermembrane of the mitochondria to the intermembrane space. 18. FADH2 looks very similar to another product of the CAC. What other product of the CAC is it similar to and what is this molecule’s function in cell respiration? It is very similar to NADH, as it is also an electron carrier. It drops its electrons off at the electron transport chain further down the chain than NADH because it is a lower energy electron carrier. 9.4 Oxidative phosphorylation (OP)___________________________________________ 19. Where does Oxidative Phosphorylation (OP) take place? Identify the major organelle and any membranes or spaces within that organelle. In general, OP takes place in the mitochondria, but you need to know more details about where exactly in the mitochondria to understand OP. Important membrane of the mitochondria for OP: Inner membrane The inner membrane of the mitochondria had many electron transport chains (ETC) embedded in its phospholipid bilayer. The ETC is made up of protein pumps and electron transporters. Important spaces of the mitochondria for OP: Matrix and Intermembrane Space Protons also called Hydrogen ions (positive ions, often represented as + or H+) are pumped through the protein pumps of the ETC from the Matrix to the Intermemebrane Space of the mitochondria. H+ are concentrated in the Intermembrane space, producing a gradient (more H+ in the intermembrane space, less H+ in the matrix). 20A. What are the major reactants of OP? NADH and FADH2 Oxygen Hydrogen ions (H+), AKA: protons 20B. NADH and FADH2 is one of the major reactants for OP. What part of these major reactants is being used by the ETC? (HINT: What are they carrying?) The Electrons they carry (remember, these electrons were pulled from glucose) are given to the electron transport chain protein pumps. 20C. Describe how the major reactants identified in the previous question are used by the ETC. The energy from the electrons is transferred to the protein pumps of the ECT. The pumps use this energy to pump Hydrogen ions (H+) from lower concentration of Hydrogen ions in the mitochondrial matrix to higher concentration of Hydrogen ions in the Intermembrane space. The ETC protein pumps are pumping H+ from low to high. This requires ENERGY. Where does this energy to pump H+ from low to high concentration across the innermembrane of the mitochondria come from …the electrons! 20D. What (reactant molecule) causes the electrons to move from one part of the ETC to the next? Oxygen (in the air you breathe, one of the major reactants of cell respiration) is very electronegative (this means it LOVES electrons and wants them more than other atoms) pulls, so to speak, electrons through the ETC from one part of the chain to the next until it grabs them at the very last protein of the ETC. The oxygen with these electrons then combines with H+ ions to create water…water is one of the major products of this process. 21. As a result of electron transfer from one protein of the electron transport chain to the next, ___Protons H+______(ions) are actively transported from the matrix of the mitochondria to the intermembrane space. Why does the transport of the ions identified above require energy? There is a lower concentration of Hydrogen ions (H+) in the mitochondrial matrix and a higher concentration of Hydrogen ions (H+) in the Intermembrane space. The ETC protein pumps are pumping H+ from low to high. This requires ENERGY. Think of it as rolling a ball up a hill (low to high) vs. down a hill (high to low). Which one requires an input of energy. UPHILL (low to high)! 22A.The gradient of H+ ions (AKA: protons) in the intermembrane space (created by the electron transport chain) is called the proton motive force. Can H+ ions diffuse from the intermembrane space to the matrix through… i. ETC protein pumps? EXPLAIN why or why not. ii. phospholipid bilayer of the inner membrane? EXPLAIN why or why not. iii. ATPsynthase? EXPLAIN why or why not? H+ ions can move down their gradient (high to low) back into the matrix from the intermembrane space only by going through the ATPsynthase. IMPORTANT: H+ ions cannot move back through the proteins of the ETC (these are a one way street, from matrix to intermembrane space only) or through the phospholipid bilayer of the inner membrane of the mitochondria (because H+ are charged, polar molecules and the membrane in mainly nonpolar (see chapter 7). 22B. Describe how the mitochondria uses the gradient of H+ ions/proton motive force to produce ATP. (HINT: discuss the ATP synthase) As H+ ions diffuse through the ATP synthase down their concentration gradient from (high to low.) This results in conformational changes that open up catalytic sites on the ATP synthase where ADP is joined to Phosphate to make ATP. 23. What are the major products of OP? ATP NAD+ Water 24. What product of OP is most important (purpose of Cell respiration)? ATP 25. Summarize the travel of an electron through cellular respiration starting with an electron that is pulled from a glucose molecule in the cytoplasm and ending with the electron associating with oxygen in the last stage of cell respiration: Food NAD+ NADH electron transport chain proteins oxygen 26. SUMMARY OF 3 MAJOR STEPS OF CELL RESPIRATION: a. Most important molecule produced in glycolysis b. Most important molecule produced in the Krebs cycle? c. Most important molecule produced in oxidative phosphorylation? PYRUVATE NADH AND FADH2 ATP Are the compounds listed here used, produced or neither (N/A) in: Glucose Glycolysis? USED The Krebs cycle? Oxidative phosphorylation? N/A N/A N/A USED PRODUCED N/A N/A PRODUCED USED AND PRODUCED PRODUCED PRODUCED USED AND PRODUCED USED USED NADH PRODUCED PRODUCED USED NAD USED USED PRODUCED N/A O2 CO2 N/A H2O N/A ATP ADP P i 9.5 Fermentation________________________________________________________ 27. Where does fermentation occur? Cytoplasm of the cell. 28A. What metabolic step do Cellular respiration and Fermentation have in common? Glycolysis - no Oxygen required 28B. In terms of reactants, what is the major difference between fermentation and cell respiration? Fermentation does not require oxygen Cell Respiration requires oxygen 29.Which process, fermentation or cell respiration produces more ATP? Cell Resp. What are the approximate numbers of ATP produced in each process per glucose molecule? ~36-38 ATP made in Cell Respiration vs. 2 ATP in Fermentation 30.Why do scientists think glycolysis preceded the full process of cellular respiration in evolution as a process to make ATP? Early atmosphere had little oxygen, so organisms had to produce ATP without oxygen. When Oxygen became more abundant with rise of photosynthetic plants, process of cell respiration was created as a more lucrative way to make energy 9.6_____________________________________________________________________ 31.T/F Glucose is the only organic molecule that can be utilized during cellular respiration to make ATP. Fats and proteins can also be used. See fig. 9.19 32. Cellular respiration is controlled by an allosteric enzyme Phosphofructokinase at a key points in glycolysis (see figure below). Explain how Phosphofructokinase regulates the rate of respiration in the cell when… A. ATP increases When cell has made enough ATP, ATP acts as an inhibitor and will inhibit the phosphofructokinase enzyme by stabilizing the inactive form of this allosteric enzyme, which will stop gylcolysis and any cell respiration events that follow. B. ATP decreases When ATP is low in cell, ATP will no longer inhibit the phsophfructokinase enzyme, allowing gylcolysis, citric acid cycle and oxidative phosphorylation to proceed and make the necessary ATP.