Biological Science (7th Edition)
7th Edition
ISBN: 9780134678320
Author: Scott Freeman, Kim Quillin, Lizabeth Allison, Michael Black, Greg Podgorski, Emily Taylor, Jeff Carmichael
Publisher: PEARSON
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Chapter 9, Problem 7TYU
In step 3 of the citric acid cycle, the enzyme isocitrate dehydrogenase is regulated by NADH. Compare and contrast the regulation of this enzyme with the regulation of phosphofructokinase in glycolysis.
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ATP is an ALLOSTERIC INHIBITOR of the phosphofructokinase enzyme, which is a key catalyst for one of the first steps of Glycolysis. Citrate (citric acid) is a 6-carbon product of the first reaction of the Krebs Cycle (aka Citric Acid Cycle). Interestingly, Citrate enhances the inhibitory effect of ATP on phosphofructokinase. What is a likely explanation for the inhibitory effects of these molecules?
Excess ATP and Citrate signal the cell that Glycolysis should be speeded up.
Excess ATP and Citrate signal a positive feedback loop.
Excess ATP and Citrate signal the cell that Glycolysis should be slowed.
Excess ATP and Citrate compete for the active site of phosphofructokinase.
Name three enzymes from the citric acid cycle which are allosterically regulated by ATP and/or
NADH. Indicate if the binding of these effectors positively or negatively regulate the activity of
each of these enzymes
Although molecular oxygen (O2) does not participate directly in any of the reactions of the citric acid cycle, the cycle operates only when O2 is present. Explain this observation.
Chapter 9 Solutions
Biological Science (7th Edition)
Ch. 9 - Where does the citric acid cycle occur in...Ch. 9 - 2. What does the chemiosmotic hypothesis claim?
a....Ch. 9 - 3. After glucose is fully oxidized by glycolysis,...Ch. 9 - Compare and contrast substrate-level...Ch. 9 - If you were to expose cells that are undergoing...Ch. 9 - In step 3 of the citric acid cycle, the enzyme...Ch. 9 - 8. Explain the relationship between electron...Ch. 9 - 9. Cyanide (C=N–) blocks complex IV of the...Ch. 9 - Prob. 13PIATCh. 9 - SOCIETY In the 1930s, DNP was introduced as a diet...
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- Although both hexokinase and phosphofructokinase catalyze irreversible steps in glycolysis and the hexokinase-catalyzed step is first, phosphofructokinase is nonetheless the pacemaker of glycolysis. What does this information tell you about the fate of the glucose 6-phosphate formed by hexokinase? Glucose 6-phosphate must be unstable and release its phosphoryl group over time. Glucose 6-phosphate must be utilized by other metabolic pathways. Glucose 6-phosphate must allosterically inhibit phosphofructokinase, but not hexokinase. Glucose 6-phosphate must be wasted when it is produced in excess.arrow_forwardClassify each reaction or process as one that decreases or replenishes the pool of oxaloacetate available for the activity of the citric acid cycle. Assume the reactions proceed in the forward direction. Decreases the oxaloacetate pool Replenishes the oxaloacetate pool Answer Bank reaction catalyzed by PEP carboxykinase reactions of gluconeogenesis reaction catalyzed by malic enzyme reaction catalyzed by PEP carboxylase reaction catalyzed by pyruvate carboxylasearrow_forwardTaking into consideration glycolysis, the pyruvate dehydrogenase complex and the citric acid cycle, how many substrate level phosphorylation events occur from a single molecule of glucose? 6 substrate level phosphorylation events 4 substrate level phosphorylation events 3 substrate level phosphorylation events 2 substrate level phosphorylation events None of the above answers are correctarrow_forward
- Perform a pyruvate dehydrogenase reaction and a single turn of the citric acid cycle using an oxaloacetate molecule uniformly labeled with 18O and one pyruvate molecule uniformly labeled with 14C. Highlight the fate of all radioactively labeled atoms when complete.arrow_forwardWhy is it advantageous for citrate, the product of Reaction 1 of the citric acid cycle, to inhibit phosphofructokinase, which catalyzes the third reaction of glycolysis?arrow_forwardAssuming that the glycerol 3-phosphate shuttle is operative, a complete oxidation of three molecules of glucose (by a eukaryotic cell) into carbon dioxide and water would produce approximately ATP molecules via oxidative phosphorylation only. (Consider NADH = 2.5 ATP and FADH2 = 1.5 ATP)arrow_forward
- How many total moles of ATP are created in a cell with an ATP synthase with 8 c subunits for every 28 moles of glucose that is completely oxidized in glycolysis and the Krebs cycle? Assume that NADH is transported by the malate aspartate shuttle.arrow_forwardMalate dehydrogenase is an enzyme that converts malate to oxaloacetate in the last stage of the TCA Cycle (citric acid cycle/Krebs cyde), represented by the following equation: NAD+ Malate Oxaloacetate NADH A group of students carried out an experiment to determine the optimum temperature for the activity of a commercially produced malate dehydrogenase (from yeast) at several different temperatures. A series of test tubes was set up containing 2.0 cm of phosphate buffer with a pH of 7.5, 0.1 cm? of NADH, 0.1 cm of malate dehydrogenase and 0.7 cm3 of water. The tubes were incubated in water baths at the various temperatures for 5 minutes. At certain time intervals each tube was placed in a colorimeter, set at an absorbance value of 1.0. The reaction was then started by adding 0.1 cm? of oxaloacetic acid to the tube. Enzyme activity was measured by following the decrease in absorbance for 120 seconds. The experiment was repeated to give duplicate results. Enzyme activity was then…arrow_forwardThe citric acid cycle is mainly controlled at the first two NADH-producing reactions catalyzed by ___________ and ___________, respectively. Group of answer choices isocitrate dehydrogenase; alpha-ketoglutarate dehydrogenase complex pyruvate dehydrogenase complex; alpha-ketoglutarate dehydrogenase complex alpha-ketoglutarate dehydrogenase complex; malate dehydrogenase isocitrate dehydrogenase; malate dehydrogenase pyruvate dehydrogenase complex; isocitrate dehydrogenasearrow_forward
- Why, do you suppose, the coenzyme for the reaction in the citric acid cycle that is catalyzed by succinate dehydrogenase is FAD and not NAD+?arrow_forwardThe citric acid cycle is frequently described as the major pathway of aerobic catabolism, which means that it is an oxygen-dependent degradative process. However, none of the reactions of the cycle directly involve oxygen as a reactant. Why is the pathway oxygen dependent?arrow_forwardFor 30 moles of glucose that is completely oxidized in the glycolysis down to the Krebs cycle, what is the total moles of ATP produced in a cell with an ATP synthase possessing 8 c subunits? Assume that the malate aspartate shuttle is used for NADH transport.arrow_forward
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