Module 4: Practice Quizzes and Module Quiz (Ch 16, 17, 18, 19, 20, 21) – Flashcards

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question
A suspension of yeast cells is being grown under anaerobic conditions such that glucose is degraded to ethanol and carbon dioxide. If one wishes to follow this process by monitoring the release of 14CO2, at which positions in the glucose molecule would the 14C label need to be incorporated?
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carbons 3 and 4
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If an inhibitor of alcohol dehydrogenase is added to the above suspension, the cells rapidly die because
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the NAD+ needed to keep glycolysis going is not being recycled so the entire process is shut down and no ATP is produced. Correct. The inability to regenerate NAD+ for the glyceraldehyde-3-phoshate dehydrogenase reaction will bring glycolysis to a halt.
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When glyceraldehyde-3-phosphate oxidatively converted to 1,3-bisphosphoglycerate in the presence of phosphate and glyceraldehyde-3-phosphate dehydrogenase, what is reduced?
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NAD+ Correct. NAD+ is the electron sink for glycolysis. When an intermediate is oxidized, NAD+ is reduced to NADH.
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The mechanism of glyceraldehyde-3-phosphate dehydrogenase does NOT involve
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phosphorylation of the substrate using ATP. Correct. Phosphorylation of the substrate occurs but not at the expense of ATP.
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Although glucose is the major sugar degraded by the glycolytic pathway, other sugars such as galactose and fructose are also derived from food. These sugars
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are metabolized by the glycolytic pathway by conversion to intermediates in the pathway. Correct. Both galactose and fructose enter the glycolytic pathway by conversion to intermediates in the pathway. Fructose is converted to fructose 1-phosphate and then to glyceraldehyde and dihydroxyacetone phosphate. Glyceraldehyde is converted to glyceraldehyde 3-phosphate. Thus, two glycolytic intermediates are produced from fructose. Galactose undergoes four conversions to produce glucose 6-phosphate, a glycolysis intermediate.
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The three major regulatory enzymes in the glycolytic pathway are
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hexokinase, phosphofructokinase, and pyruvate kinase. Correct. These three allosteric enzymes serve key regulatory roles in glycolysis.
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Well into exercise, the ratio of ATP/AMP in muscle cells decreases. What effect does this ratio reduction have on the activity of phosphofructokinase and pyruvate kinase?
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Both enzymes are increased in activity due to lack of allosteric binding of ATP. Correct. If the energy charge falls, glycolysis is stimulated and both phosphofructokinase and pyruvate kinase will increase in activity.
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The processes of gluconeogenesis and glycolysis are said to be reciprocally regulated. This means that
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molecules that inhibit (or activate) one process often have the opposite effect on the other. Correct. The idea behind reciprocal control is that a molecule that affects a degradation pathway will affect a synthetic pathway in an opposite manner.
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In glycolysis, the isomerization of glucose to fructose is necessary because
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it is needed to ensure that equal 3-carbon units can be made. Correct. The creation of equal 3-carbon units allows the same enzymatic machinery to use both of the molecules from glucose after it is split, such that a separate glycolytic pathway is unnecessary.
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Why might a cancer cell show a preference for glycolysis, even in the presence of oxygen?
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Tumor cells can readily form a low oxygen environment as they grow. Correct. Rapid growth of tumor cells often creates hypoxic conditions in the interior of a tumor, favoring tumor cells that utilize glycolysis and can survive under those conditions.
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In actively contracting skeletal muscle tissue, the major way in which glucose is metabolized is via
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lactic acid fermentation. Correct. Because the rate of glycolysis exceeds that of the citric acid cycle, most glucose is converted to lactate in actively contracting muscle tissue.
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Enzymes that catalyze the same reaction but differ in amino acid sequence are called
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isozymes. Correct. The muscle and heart forms of lactate dehydrogenase are examples of isozymes.
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The process of glycolysis results in the formation of two high-energy phosphate bonds (in the form of ATP). How many high-energy phosphate bonds are consumed during the process of gluconeogenesis using pyruvate as a starting material?
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6 Correct. Four ATP and two GTP are needed to produce glucose from pyruvate.
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What product of contracting muscle tissue is used by the liver as starting material for gluconeogenesis?
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lactate Correct. Lactate is transported by the blood stream to the liver where it serves as a starting material for the production of glucose.
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While glycolysis can occur in most cells, the major site of gluconeogenesis is limited to two tissues. Which of the following is NOT one of them?
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muscle Correct. Although lactate from muscle tissue can be used as a starting material for the synthesis of glucose, gluconeogenesis does not occur in muscle tissue.
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Type 2 diabetes is a disease characterized by overproduction of glucose by the liver and its underutilization by other organs. Which of the following is NOT a cause of diabetes?
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the generation of enzymes in the blood that rapidly degrade insulin after release from the pancreas Correct. Neither type of diabetes involves rapid degradation of insulin in the bloodstream.
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The generation of glucose from glucose 6-phosphate occurs in which membrane-bound organelle(s)?
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endoplasmic reticulum
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Which of the following statements is true of fructose 1,6-bisphosphate but not of fructose 6-phosphate?
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It contains two phosphate groups.
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If both glycolysis and gluconeogenesis were simultaneously operating at the same rate, which of the following statements would be TRUE?
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Two ATP and two GTP molecules would be consumed per reaction cycle. AND Hypoglycemia would eventually occur unless food was consumed.
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Type 2 diabetes is most commonly diagnosed _____ in life and involves _____.
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later; insulin resistance
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If energy levels are low in a cell, the concentration of _____ will be high and _____ will be turned on.
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AMP; glycolysis
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Red blood cells generate all ATP through glycolysis because they lack:
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mitochondria
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Which of the following situations or phrases most accurately describes the citric acid cycle?
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"All roads lead to Rome." Correct. In many ways, the citric acid cycle can be considered as the centerpiece of cellular metabolism, with a variety of catabolic and anabolic pathways leading to and from it.
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In the reaction catalyzed by the pyruvate dehydrogenase complex, the two carbons constituting the acetyl group are
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transferred to the lipoamide by an earlier intermediate in the process. Correct. The two carbons are first attached to thiamine pyrophosphate and then transferred to the lipoamide.
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Which of the following is NOT a product of the reaction catalyzed by pyruvate dehydrogenase complex?
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pyruvate Correct.
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Which of the following is NOT a coenzyme necessary in the function of pyruvate dehydrogenase complex?
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ubiquinone Correct.
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Pyruvate dehydrogenase complex falls within which size range?
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4-10 million daltons
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The core of the pyruvate dehydrogenase complex is made up of eight catalytic _____ that make up the _____ component.
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trimers; E2
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Beriberi is a disease caused by a deficiency of which vitamin?
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vitamin B1 (thiamine)
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Some symptoms of beriberi include:
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both muscle weakness and distorted skin sensation.
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Entry to the citric acid cycle involves the generation of acetyl CoA. The enzyme that catalyzes the production of acetyl CoA is _____. This enzyme is negatively regulated by _____ in a high-energy charge situation.
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pyruvate dehydrogenase; NADH
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The pyruvate dehydrogenase complex is regulated by:
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phosphorylation. allosteric interactions. covalent modifications. *All of the above
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Which enzyme of the citric acid cycle most closely resembles the pyruvate dehydrogenase complex in terms of its structure, organization, and the reaction it performs?
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α-ketoglutarate dehydrogenase Correct. The α-ketoglutarate dehydrogenase enzyme is structurally and functionally homologous to the pyruvate dehydrogenase complex.
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Although the pyruvate dehydrogenase complex is subject to allosteric control, especially inhibition by reaction products, the main regulatory process controlling the enzyme's activity in eukaryotes is
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phosphorylation by ATP that turns off the complex and dephosphorylation that turns it on. Correct. High levels of ATP are indicative of a situation in which no further ATP is needed and thus the enzyme is turned off by phosphorylation.
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In going from acetyl-CoA to succinate, two carbons have entered the cycle and two have been released as CO2. Why is the cycle not considered as complete at this point?
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The oxaloacetate used to initiate the cycle must be regenerated. Correct. One must replace what one used to start the cycle (oxaloacetate) in order to keep it going.
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Assuming that pyruvate was labeled with radioactive 14C in its middle (keto) carbon, where would the radiolabel appear after one turn of the citric acid cycle?
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equally divided between the two carboxyl groups of oxaloacetate Correct. The "randomization" of label between the two carboxyl groups results from the reaction catalyzed by fumarase.
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In the reaction catalyzed by succinyl-CoA synthetase
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a succinylphosphate transfers its phosphate to a histidyl residue. Correct. The succinylphosphate generated in the first step of the reaction transfers its phosphate to a histidine in the next step.
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Of the enzymes of the citric acid cycle, which is not a freely soluble enzyme?
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succinate dehydrogenase Correct. Succinate dehydrogenase in associated with the inner mitochondrial membrane with one of its products (FADH2) directly entering the electron transport chain.
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The purpose of anaplerotic reactions is
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to replenish the citric acid cycle if it becomes depleted of intermediates by biosynthetic demands. Correct. One must have some oxaloacetate present in order to start the cycle. If it is depleted, it must be replenished before the cycle can operate.
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Although the glyoxylate cycle is not present in animals, many plants and animals can use this modified form of the citric acid cycle. The glyoxylate cycle is beneficial in that
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it allows the organisms which possess it to grow on acetate. Correct. The ability to use alternate carbon sources provides a metabolic versatility.
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A person suffering from beriberi (deficiency of vitamin B1) lacks the ability to readily produce
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succinyl CoA. Correct. TPP is derived from vitamin B1, and is a necessary cofactor in the α-ketoglutarate dehydrogenase enzyme complex needed to catalyze the production of succinyl CoA.
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Glucose derived from citric acid cycle molecules must do so via
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oxaloacetate. Correct. Oxaloacetate can be shuttled into glucose via the gluconeogenesis pathway.
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Oxygen is not used at any point in the citric acid cycle. However, the cycle will not work without oxygen because
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oxygen is needed to regenerate electron carriers. Correct. In the same way that fermentation regenerates the electron carriers needed for glycolysis, oxygen is needed to serve as the final electron acceptor that will allow a molecule like NADH to return to NAD+.
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In order for an electron transfer reaction to be energetically spontaneous, which of the following must be TRUE?
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The change in reduction potential, ΔEo, must be positive. Correct. A positive value for ΔEo will give a negative value for ΔGo.
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Which of the following is not a mobile or diffusible electron carrier in the mitochondrial electron transport chain?
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FAD Correct. FAD is a component of complex II or succinate dehydrogenase. It feeds electrons directly into the electron transport chain.
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Of the electron transfer complexes associated with the inner mitochondrial membrane, which is not involved in generation of a proton gradient?
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succinate-Q reductase (complex II) Correct. The passage of electrons through complex II does not contribute to the proton gradient.
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What is the source of electrons at complex II (succinate-Q-reductase)?
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FADH2 from the citric acid cycle Correct. FADH2 is generated in the citric acid cycle (in the succinate dehydrogenase-catalyzed conversion of succinate to fumarate) and it enters the electron transport chain at complex II (succinate-Q-reductase).
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Which of the following describes the direction of proton movement relative to electron transfer and phosphorylation?
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Electron transfer pumps protons out of the matrix. As the protons reenter through the ATP synthase, ATP is produced in the matrix. Correct. All directions are correct with respect to both electron transfer and phosphorylation.
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For a given reduced/oxidized molecular pair (X-/X), a negative reducing potential suggests that the
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X has a lower affinity for electrons than H2 does. Correct. The predominance of the reduced hydrogen gas implies that the electron has a higher affinity for the reference standard hydrogen, making the value negative.
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Consider a substance that can exist in an oxidized form X and a reduced form X-. Such a pair is called a(n):
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redox couple
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Which of the following statements points to the endosymbiotic event yielding intercellular mitochondria?
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Mitochondria contain their circular DNA. Mitochondria have a double membrane. Mitochondria contain specific transcription and translation machinery. *All of the above
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Which of the following proteins involved in the respiratory chain exists as a monomer?
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cytochrome c
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Which of the following may be due to free-radical injury?
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emphysema Parkinson disease Duchenne muscular dystrophy *All of the above
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Which of the following is NOT a part of the Mitchell chemiosmotic hypothesis?
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High-energy phosphorylated intermediates that serve as phosphate donors to ADP are generated as a result of electron-transfer reactions. Correct. High energy phosphorylated intermediates are not a part of Mitchell's chemiosmotic hypothesis.
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Proton flow through the ATP synthase enzyme
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results in the release of ATP from its tightly bound state in the active site. Correct. Although readily produced in the active site, ATP is only released when protons flow through the enzyme.
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The process of glycolysis occurs in the cytoplasm. The electrons from the NADH generated during glycolysis
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may enter the electron transport chain either at the level of NADH or FADH2, depending on the shuttle system used to transport them into the mitochondria. Correct. The glycerol-3-phosphate shuttle allows electrons from cytoplasmic NADH to enter the mitochondrial electron transport chain at the level of FADH2 and the malate-aspartate shuttle at the level of NADH.
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The uncoupler dinitrophenol (DNP) prevents ATP synthesis while allowing electron transport to proceed because
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DNP is capable of transporting protons across the membrane, dissipating the proton gradient. Correct. DNP effectively "short circuits" the proton motive force such that it is dissipated before it can be used to drive ATP production.
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The presence of uncoupling proteins allows _____ energy from the mitochondrial electron transport chain to be used for ATP synthesis and ______ for the production of heat.
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less; more Correct. Regulated uncoupling can balance the needs of the organism for ATP and heat.
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The path taken by electrons to water from NADH generated during the citric acid cycle will NOT pass though
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FAD. Correct. FAD is only used for transport of NADH electrons (in some cases) from outside the mitochondria, not ones generated within the mitochondria in the citric acid cycle. NADH from the citric acid cycle also does not pass though the FAD found in Complex II of the electron transport chain.
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The energy generation of ATP using ATP synthase can be thought of the reverse reaction of what chemical reaction?
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ATP hydrolysis and proton movement against a gradient Correct. ATP synthase in reverse involves the favorable ATP hydrolysis that can drive the unfavorable pumping of protons against a gradient.
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Like other molecular motors, the rotation of a bacterial flagellar apparatus requires a source of energy. What is used to provide energy for this type of molecular motor?
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proton gradient across membrane Correct. The proton gradient across the plasma membrane provides the source of energy driving flagellar motion.
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Peter Mitchell proposed the _____ hypothesis that describes how _____ and _____ are coupled.
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chemiosmotic; electron transport; ATP synthesis
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The regulation of the rate of oxidative phosphorylation by the ADP level is called _____ control.
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acceptor
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Glucose is the most stable hexose because the hydroxyl groups are all in the _____ position.
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equatorial *This will be counted wrong, but it is correct. P283 in book. Mentioned to Prof.
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The key regulatory enzyme for glycolysis is _____.
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phosphofructokinase
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_____ are enzymes that catalyze the transfer of a phosphoryl group from ATP to an acceptor.
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Kinases
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The first irreversible enzymatic reaction unique to a metabolic pathway is called the _____ step.
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committed
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_____ mediate the thermodynamically downhill movement of glucose across plasma membranes.
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Glucose transporters
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What two 3-carbon molecules are generated by the cleavage of fructose-1,6-bisphosphate?
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glyceraldehyde-3-phosphate and dihydroxyacetone phosphate
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What are the primary metabolic fates of pyruvate?
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ethanol lactate acetyl CoA *All the above.
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The process of forming glucose from amino acids is called _____.
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gluconeogenesis
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Some amino acids are converted to glucose via conversion to pyruvate and _____.
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oxaloacetate
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The enzyme that carboxylates pyruvate is _____.
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*Didn't get correct. Not sure.
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ATP in the reaction catalyzed by PEPCK is use to fix _____ to biotin
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carbon dioxide
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The first step in gluconeogenesis is the _____ of pyruvate to form oxaloacetate.
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carboxylation
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E1 of the pyruvate dehydrogenase complex requires the coenzyme _____ for proper activity.
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Answer should be TPP but not accepted.
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High-energy charge, which results in increasing concentration of NADH, _____ the activity of PDH.
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inhibits
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The citric acid cycle is also known as the:
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Krebs cycle and the tricarboxylic acid cycle.
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Pyruvate is decarboxylated by which subunit of the PDH?
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E1
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What are the steps involved (in order) in the conversion of pyruvate to acetyl CoA?
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decarboxylation, oxidation, transfer to CoA
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Pyruvate dehydrogenase is _____ when ATP/ADP ratios are high.
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inhibited
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Carbons from carbohydrate enter the citric acid cycle in the form of _____.
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acetyl CoA
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In the citric acid cycle, the _____ is produced by a substrate-level phosphorylation.
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GTP *CAREFUL! This is tricky. In glycolysis it is ATP!
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In general, the citric acid cycle is inhibited under _____ (high, low) energy conditions.
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high
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What molecule initiates the citric acid cycle by reacting with oxaloacetate?
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acetyl CoA
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The direct movement of substrates from one enzyme to the next is called:
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substrate channeling.
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Formation of citrate from acetyl CoA and oxaloacetate is a(n) _____ reaction.
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condensation
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A strong oxidizing agent has a tendency to _____ (accept, donate) electrons.
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accept
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Another name for coenzyme Q is _____.
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ubiquinone
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ytochrome _____ is the only water-soluble cytochrome of the electron-transport chain.
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c
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The transfer of a single electron to O2 forms the reactive _____ ion.
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superoxide
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_____ is an enzyme that scavenges H2O2 and converts it to molecular oxygen and water.
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Catalase
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_____ are the result of uncontrolled electron transfer to oxygen.
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Oxygen radicals
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Electron flow down the electron-transport chain leads to the:
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transport of protons across the inner mitochondrial membrane from inside the matrix to the intermembrane space.
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Which of the following does NOT pump protons? Complex I Complex II Complex III Complex IV
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Complex II
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What is a cytochrome?
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a protein that transfers electrons, and that also contains a heme prosthetic group
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