METABOLIC PATHWAYS

During the metabolism of a fatty acid side chain containing 11 carbons, how many water molecules are used and how much FADH2 is produced? Question 14 Answer Choices A. 4 molecules of water, 4 FADH2 B. 4 molecules of water, 8 FADH2 C. 5 molecules of water, 5 FADH2 D. 3 molecules of water, 6 FADH2

A. 4 molecules of water will be used and 4 FADH2 will be produced during the oxidation of an 11-C fatty acid. Fatty acid metabolism occurs by removal of two carbons per round of β-oxidation until the final two or three carbons are reached, depending on whether the original fatty acid chain had an even or odd number of carbons in total. Since the side chain in the question has a total of 11 carbons, there will be four rounds of β-oxidation, leaving the final three carbons at the end of the process. Each β-oxidation uses one water molecule and produces one FADH2 (as well as one NADH although the question does not ask about NADH).

How much net ATP would be produced if three molecules of glucose were used during anaerobic cellular respiration? Question 4 Answer Choices A. 6 B. 24 C. 36 D. 12

A. 6 net ATP would be produced if three molecules of glucose were used during anaerobic cellular respiration. In an anaerobic environment, only glycolysis can occur. This process produces a net of 2 ATP per glucose, so three glucose molecules would produce 6 ATP total.

Which of the following best describes the primary purpose of the pentose phosphate pathway? Question 9 Answer Choices A. To produce ribose-5-phosphate that can be used to synthesize nucleotides B. To produce high levels of ATP C. To produce glucose-6-phosphate that is incorporated into glycogen D. To produce ribose-5-phosphate that is stored in skeletal muscle for use as rapid energy

A. The primary purpose of the pentose phosphate pathway is to produce ribose-5-phosphate that can be used to synthesize nucleotides (as well as NADPH, and a few other intermediates). Glucose-6-phosphate is shunted from glycolysis to the pentose phosphate pathway; the pentose phosphate pathway does not produce glucose-6-phosphate, rather glu-6-P is actually a substrate of the pathway. The pentose phosphate pathway is not a source of cellular ATP and ribose-5-phophate is not stored for energy.

Which of the following is NOT produced by the liver as an intermediate step in ketogenesis? Question 15 Answer Choices A. Acetoacetate B. Acetyl-CoA C. Acetone D. β-hydroxybutyrate

B. Acetyl-CoA is NOT produced by the liver as an intermediate step in ketogenesis. Acetone, acetoacetate, and β-hydroxybutyrate are all formed by the liver as part of ketogenesis. These products are then distributed to the cells which then convert them into acetyl-CoA for use in the Krebs cycle, but the acetyl-CoA itself is not made by the liver.

Which of the following is the most oxidized compound produced in glycolysis? Question 11 Answer Choices A. Glucose-6-phosphate B. Pyruvate C. Oxaloacetate D. Glucose

B. Pyruvate is the most oxidized compound produced in glycolysis. Of the compounds listed, only pyruvate, glucose, and glucose-6-phosphate are involved in glycolysis. Oxaloacetate is part of the Krebs cycle and is not the correct answer. Glucose is the starting material for glycolysis and is therefore not produced in glycolysis (this is not the correct answer) and addition of a phosphate in the first step of glycolysis to form glucose-6-phosphate is not an oxidation-reduction reaction (this is not the correct answer). Therefore pyruvate is the most oxidized compound as well as being the final product of glycolysis.

Which of the following is/are products of both glycolysis and the electron transport chain? I. ATP II. NADH III. Oxygen IV. FADH2 Question 3 Answer Choices A. I, II, and III B. I and III C. I D. II and IV

C. ATP (I below) is a product of both glycolysis and the electron transport chain. I. ATP II. NADH III. Oxygen IV. FADH2 Item I is true: ATP is produced in both the glycolysis and the electron transport chain. Item II is false: NADH is not produced by the electron transport chain. Items III and IV are false: oxygen and FADH2 are not produced in either of these processes.

Which of the following situations would be most likely to cause glycogenolysis? Question 19 Answer Choices A. Stimulation of the parasympathetic nervous system B. Stimulation of β-cells in the pancreas C. An overnight fast D. Consumption of a large meal

C. An overnight fast would lead to glucagon release, resulting in glycogenolysis by the liver and the release of glucose into the blood. Glycogenolysis is stimulated by the sympathetic nervous system (fight or flight), not parasympathetic. Consumption of a large meal and stimulation of pancreatic β-cells would both increase insulin release and cause glycogen synthesis, not glycogen breakdown.

Antimycin is used as a piscicide (fish poison) because it inhibits Complex III of the electron transport chain. Blocking the flow of electrons through Complex III will produce which of the following effects? I. Complex I (NADH dehydrogenase) will persist in a reduced state. II. Complex IV (cytochrome C oxidase) will persist in a reduced state. III. Oxygen consumption will be decreased. Question 7 Answer Choices A. I, II, and III B. II and III only C. I and III only D. III only

C. Antimycin is used as a piscicide (fish poison) because it inhibits Complex III of the electron transport chain. Blocking the flow of electrons through Complex III will produce the effects listed in Items I and III only. I. Complex I (NADH dehydrogenase) will persist in a reduced state. II. Complex IV (cytochrome C oxidase) will persist in a reduced state. III. Oxygen consumption will be decreased. Reduced electron carriers like NADH and FADH2 transport electrons from the reactions of glycolysis, the pyruvate dehydrogenase complex, and the Krebs cycle to the electron transport chain. Electrons are then relayed through the various proteins of the chain and finally to oxygen, which is reduced to water. Inhibiting any part of the electron transport chain will halt the transfer of electrons. Item I is true: Blocking electron transport at Complex III will result in a build-up of electrons at proteins earlier in the chain. Because these earlier proteins, including Complex I, cannot pass their electrons off, they will persist in the reduced state ("Gain of Electrons is a Reduction"). Item II, however, is false: Proteins later in the chain can release their electrons, but cannot replenish them. These later proteins, including Complex IV, will persist in the oxidized state ("Loss of Electrons is an Oxidation"). Electrons meeting a roadblock at Complex III will never reach oxygen. Item III is true: Thus, oxygen consumption (reduction) will be decreased. It is important to note that inhibiting the electron transport chain diminishes the proton gradient and compromises ATP synthesis. This is why antimycin is so toxic to cells.

Due to electron transport in a eukaryotic cell: Question 5 Answer Choices A. the pH in the intermembrane space is higher because protons are pumped into the matrix of the mitochondria. B. the pH in the intermembrane space is lower because protons are pumped into the matrix of the mitochondria. C. the pH in the matrix of the mitochondria is higher because protons are pumped across the inner membrane of the mitochondria. D. the pH in the matrix of the mitochondria is lower because protons are pumped across the inner membrane of the mitochondria.

C. Due to electron transport in a eukaryotic cell, the pH in the matrix of the mitochondria is higher because protons are pumped across the inner membrane of the mitochondria. Protons are pumped across the inner membrane of the mitochondria, out of the matrix and into the intermembrane space (the statements "the pH in the intermembrane space is lower because protons are pumped into the matrix of the mitochondria" and "the pH in the intermembrane space is higher because protons are pumped into the matrix of the mitochondria" are wrong), resulting in an increase in the pH of the matrix (the statement "the pH in the matrix of the mitochondria is higher because protons are pumped across the inner membrane of the mitochondria" is correct and "the pH in the matrix of the mitochondria is lower because protons are pumped across the inner membrane of the mitochondria" is wrong).

In a culture of mammalian skeletal muscle cells, the consumption of oxygen and glucose is measured. Which of the following would occur in response to inhibition of electron transport? Question 10 Answer Choices A. Oxygen consumption will increase, and glucose consumption will increase. B. Oxygen consumption will decrease, and glucose consumption will decrease. C. Oxygen consumption will decrease, and glucose consumption will increase D. Oxygen consumption will increase, and glucose consumption will decrease.

C. In a culture of mammalian skeletal muscle cells, the consumption of oxygen and glucose is measured. Oxygen consumption will decrease, and glucose consumption will increase in response to inhibition of electron transport. In the absence of electron transport, oxygen is not needed (it is the final electron acceptor in the transport chain) so the consumption of oxygen would decrease. Since the electron transport chain is not available to make energy (ATP) the cells will rely solely on anaerobic respiration - glycolysis. Further, since the energy demands of the cells have not changed, and since glycolysis makes fewer ATP than electron transport, the rate of glycolysis will have to increase to keep the level of ATP normal. Thus, glucose consumption would increase.

Which of the following is true regarding Krebs cycle regulation? Question 18 Answer Choices A. It is stimulated by increased NADH levels. B. It is inhibited by increased ADP levels. C. It is inhibited by increased ATP levels. D. It is stimulated by increased FADH2 levels.

C. It is true that the Krebs cycle is inhibited by increased ATP levels. Since ATP is a product of oxidative glucose catabolism, high levels of ATP indicate that the cell does not need to break down more glucose to produce more ATP. The Krebs cycle is stimulated by high ADP levels. Additionally, the Krebs cycle is inhibited by increased NADH levels. FADH2 levels are not involved in the regulation of Krebs.

Which of the following processes occur in the matrix of the mitochondria? I. electron transport chain II. glycolysis III. Krebs cycle IV. fatty acid oxidation Question 6 Answer Choices A. I, III, and IV B. III only C. III and IV D. I and II

C. Of the following processes, III and IV occur in the matrix of the mitochondria. I. electron transport chain II. glycolysis III. Krebs cycle IV. fatty acid oxidation Item I is false: Electron transport occurs across the inner membrane of the mitochondria. Item II is false: Glycolysis occurs in the cytoplasm. Items III and IV are true: the Krebs cycle and fatty acid oxidation both occur in the matrix of the mitochondria.

In the presence of glucose-6-phosphate dehydrogenase, what will the oxidative phase of the pentose phosphate pathway produce? Question 17 Answer Choices A. Fructose-6-phosphate and erythrose-4-phosphate B. Fructose-6-phosphate and 2 NADH C. Ribulose-5-phosphate and 2 NADPH D. Ribulose-5-phosphate and 1 NADPH

C. The oxidative phase of the pentose phosphate pathway produces ribulose-5-phosphate and two NADPH. NADH is not made by this pathway. Fructose-6-phosphate and erythrose-6-phosphate are both produced by it, but in the non-oxidative phase.

Arsenite inhibits the pyruvate dehydrogenase complex. What would be true of a patient exposed to high levels of arsenite? Question 13 Answer Choices A. Electron transport will halt due to the inhibition of the second complex by arsenite. B. Arsenite exerts its effect primarily in the cytoplasm. C. Krebs cycle activity will increase to offset the action of the inhibitor. D. Expired carbon dioxide will decrease.

D. A patient exposed to high levels of arsenite would begin to expire less carbon dioxide. This would occur because cellular respiration is being halted before decarboxylation occurs. Normally a single carbon dioxide per pyruvate is released in the pyruvate dehydrogenase complex and the remaining two are released in the Krebs cycle. Note that the pyruvate dehydrogenase complex is located in the mitochondrial matrix (thus arsenite would not exert its effect in the cytoplasm) and that the second complex in the electron transport chain is succinate dehydrogenase (arsenite would not likely impact this either). If no acetyl-coA is being produced from pyruvate, the activity of the Krebs cycle is likely to decrease, not increase.

In protein catabolism, what reaction allows for the production of NADH as part of the process? Question 16 Answer Choices A. Dehydration B. Phosphodiester bond formation C. Peptide bond formation D. Amino acid deamination

D. Amino acid deamination is occurring at the step in protein catabolism (breakdown) when NADH is also formed. This is just prior to the creation of ammonia as part of this process. Dehydration helps to form polymers, not break them down. Peptide bonds are specific to the creation of proteins and phosphodiester bonds create the backbone for DNA. Note that you didn't have to know that deamination was the step where NADH was created, but should have been able to eliminate the other choices as not part of protein breakdown.

A patient suffering from hypoglycemia is treated with new glucocorticoid that selectively promotes gluconeogenesis for a prolonged period of time. Which of the following best characterizes the patient after treatment? Question 12 Answer Choices A. Decreased serum glucose and decreased glycolytic activity B. Decreased serum glucose and increased glycolytic activity C. Increased serum glucose and increased glycolytic activity D. Increased serum glucose and decreased glycolytic activity

D. Following treatment with the new drug that promotes gluconeogenesis for a prolonged period of time, the patient has increased serum glucose and decreased glycolytic activity. Gluconeogenesis involves the generation of glucose from metabolic intermediates and would help rectify the hypoglycemia in the patient. Additionally, gluconeogenesis functions in opposition to glycolysis, thus simultaneous activation of both pathways would result in futile cycling and would not occur.

Which of the following is LEAST likely to occur in an individual with uncontrolled diabetes? Question 8 Answer Choices A. There is an increase in the amount of acetyl-coA produced. B. There is a decrease in the amount of NADPH produced in the pentose phosphate pathway. C. There is an increase in the amount of fatty acid oxidation. D. There is an increase in the amount of glucose-6-phosphate, which is shunted toward the pentose phosphate pathway

D. It is least likely that an individual with uncontrolled diabetes will have an increase in the amount of glucose-6-phosphate, which is shunted toward the pentose phosphate pathway. Uncontrolled diabetes results in hyperglycemia, due to either a relative or complete deficiency of insulin. This means the glucose in the blood cannot be transported into the cells. Thus, any processes that are dependent on glucose oxidation will be decreased and other processes to generate energy will be increased. Fatty acid oxidation would be increased, as the cells would break down fatty acids to produce acetyl-CoA to feed into the Krebs cycle. This would result in an increase in acetyl-CoA, not a decrease. Since glycolysis is decreased, there would be a decrease in glucose-6-phosphate that is available for the pentose phosphate pathway (not an increase) and thus, a decrease in the amount of NADPH produced by the pentose phosphate pathway.

All of the following are key processes in the production of energy in the mitochondrion EXCEPT: Question 1 Answer Choices A. the citric acid cycle. B. electron transport. C. glycolysis. D. oxidative phosphorylation.

glycolysis The citric acid cycle, electron transport, and oxidative phosphorylation are key processes in the production of energy in the mitochondrion. Glycolysis is NOT a key process in the production of energy in the mitochondrion. Glycolysis is important in energy production, but it occurs in the cytoplasm, not the mitochondrion. The other choices can be eliminated since they all occur in the mitochondrion and are therefore incorrect.

All of the following are true statements concerning the Krebs cycle EXCEPT: Question 2 Answer Choices A. oxygen is directly required for it to occur. B. two GTP are produced per glucose molecule. C. in eukaryotic cells it occurs in the matrix of the mitochondria. D. NAD+ and FAD get reduced during the cycle.

oxygen is directly required for it to occur. Concerning the Krebs cycle, the statement "oxygen is directly required for it to occur" is NOT true. Oxygen is required to run the electron transport chain during which NADH and FADH2 are oxidized. If oxygen is unavailable and the electron transport chain cannot run, there is no available NAD+ or FAD to participate in the Krebs cycle, thus we say that oxygen is only indirectly required for the Krebs cycle to occur (the statement "oxygen is directly required for it to occur" is false and the correct answer choice here). NAD+ and FAD do get reduced during the Krebs cycle (the statement "NAD+ and FAD get reduced during the cycle" is true and can be eliminated). Two GTP molecules per glucose are produced (the statement "two GTP are produced per glucose molecule" is true and can be eliminated), and in eukaryotes, the Krebs cycle does occur in the matrix of the mitochondria (the statement "in eukaryotic cells it occurs in the matrix of the mitochondria" is true and can be eliminated).