Biochem Exam 4 questions
The primary function of the citrate cycle is to oxidize____________. A. Acetate B. Pyruvate C. Oxaloacetate D. Citrate
A. Acetate
Before pyruvate enters the citrate cycle it needs to be converted to A. Acetyl-CoA B. Glucose C. Lactic acid D. Succinate E. Acetaldehyde
A. Acetyl-CoA
What is the biochemical explanation for the observed toxic effects of arsenic contaminated well water in Bangladesh? Choose the TWO best answers. A. Arsenic is converted to arsenite, which covalently modifies reduced lipoamide, thereby inhibiting activity of the pyruvate dehydrogenase complex and blocking conversion of pyruvate to acetyl-CoA. B. Arsenite forms a bidentate adduct on oxidized dihydrolipoamide and this blocks conversion of pyruvate to oxaloacetate, thereby inhibiting flux through the citrate cycle. C. The arsenic contaminated well water caused inhibition of dihydrolipoyl transacetylase, which is an enzyme subunit required for metabolism of rice starch, the source of 70% of their daily caloric intake. D. Arsenic is an electron carrier that accepts electrons from thiamin pyrophosphate and thereby short circuits the dihydrolipoamide transacetylase reaction by donating electrons directly to FAD. E. Cracked skin on the feet is caused by arsenic crystals deposited in the keratin granules of the lower extremities, and once they form, the only treatment is daily application of acai beri beri extract.
A. Arsenic is converted to arsenite, which covalently modifies reduced lipoamide, thereby inhibiting activity of the pyruvate dehydrogenase complex and blocking conversion of pyruvate to acetyl-CoA. C. The arsenic contaminated well water caused inhibition of dihydrolipoyl transacetylase, which is an enzyme subunit required for metabolism of rice starch, the source of 70% of their daily caloric intake.
Why does cyanide, an inhibitor of Complex IV in the electron transport system, also block GTP synthesis in the mitochondrial matrix by inhibiting substrate level phosphorylation in the citrate cycle? A. Because without NAD+ produced by oxidation of NADH in Complex I, NAD+-dependent redox reactions in the citrate cycle are inhibited, thereby inhibiting the citrate cycle and blocking GTP synthesis. B. Because the enzyme succinyl-CoA synthetase in the citrate cycle is also inhibited directly be cyanide, and thereby blocks substrate level phosphorylation and generation of GTP. C. Because cyanide also binds to the Fo subunit of ATP synthase, which is responsible for the substrate level phosphorylation reactions that produce 30 GTP in the citrate cycle and oxidative phosphorylation. D. Because without NADH produced by reduction of NAD+ in Complex I, NADH-dependent redox reactions in the citrate cycle are inhibited, thereby inhibiting the citrate cycle and blocking GTP synthesis. E. Because without NAD+ produced by oxidation of NADH in Complex IV, the production of H2O by the reduction of O2 in Complex I does not take place and malate dehydrogenase does not generate GTP.
A. Because without NAD+ produced by oxidation of NADH in Complex I, NAD+-dependent redox reactions in the citrate cycle are inhibited, thereby inhibiting the citrate cycle and blocking GTP synthesis.
Why is it necessary to have NADH transport systems in mitochondria? A. Cytosolic NADH cannot cross the inner mitochondrial membrane B. Reactions in the cytosol produce FAD, but need NADH C. Allow for regeneration of NAD+ in the cytosol for gluconeogenesis D. The shuttles maintain the proper ATP:ADP ratio E. It transfers NADH out of the cell
A. Cytosolic NADH cannot cross the inner mitochondrial membrane
What is the best way to explain how much energy is required to transport protons across the mitochondrial membrane as a function of energy available from redox reactions? A. Energy required to transport protons across the membrane is equal to the energy obtained from redox. B. It requires twice the amount of energy to transport protons across the membrane because of charge. C. Energy required to transport one proton across the membrane is 10X more than NADH oxidation. D. It is not possible to know because the calculations are based on the 2nd Law of Thermodynamics. E. The energy required is calculated by the Nernst equation using the gas constant under zero gravity.
A. Energy required to transport protons across the membrane is equal to the energy obtained from redox.
If the succinate dehydrogenase enzyme were mutated such that NAD+ was able to function as the cofactor instead of FAD, how would this change affect the spontaneous direction under standard conditions and the potential reversibility of the reaction under cellular conditions? Choose one or more: A. Fumarate reduction would be spontaneous under standard conditions. B. The reaction would likely be irreversible under cellular conditions. C. Succinate oxidation would be spontaneous under standard conditions. D. The reaction would likely be reversible under cellular conditions.
A. Fumarate reduction would be spontaneous under standard conditions. B. The reaction would likely be irreversible under cellular conditions.
The following are a list of statements. Select the letter which lists only the statements that are TRUE for glucokinase. A. Glucokinase is expressed only in liver and pancreatic cells. B. Glucokinase phosphorylates many 6-carbon sugars C. The reaction rate of glucokinase increases as the glucose concentration in the blood goes from 4.2 mM to 8 mM. D. Glucokinase is considered to be the key enzyme controlling blood glucose in the human body. E. In pancreatic cells, the phosphorylation of glucose by glucokinase to form glucose-6- phosphatase (G6P) activates a signaling pathway that results in the release of insulin.
A. Glucokinase is expressed only in liver and pancreatic cells. C. The reaction rate of glucokinase increases as the glucose concentration in the blood goes from 4.2 mM to 8 mM. D. Glucokinase is considered to be the key enzyme controlling blood glucose in the human body. E. In pancreatic cells, the phosphorylation of glucose by glucokinase to form glucose-6- phosphatase (G6P) activates a signaling pathway that results in the release of insulin.
Why is oxygen necessary in aerobic cellular respiration? A. It is the final electron acceptor in the electron transport chain B. It provides the hydrogen required to create a proton gradient C. It is needed for glycolysis D. It is key in creating oxaloacetic acid in the citric acid cycle E. It oxidizes NADH
A. It is the final electron acceptor in the electron transport chain
Why is the pyruvate carboxylase reaction considered an anaplerotic reaction with regard to the Citrate Cycle;; and is the enzyme pyruvate carboxylase inhibited or activated by acetyl--CoA? A. It supplies oxaloacetate to the citrate cycle;; pyruvate carboxylase is activated by acetyl--CoA. B. It supplies malate to the citrate cycle;; pyruvate carboxylase is activated by acetyl--CoA. C. It supplies oxaloacetate to the citrate cycle;; pyruvate carboxylase is inhibited by acetyl--CoA. D. It supplies pyruvate to the citrate cycle;; pyruvate carboxylase is activated by acetyl--CoA. E. None of these answers are correct.
A. It supplies oxaloacetate to the citrate cycle; pyruvate carboxylase is activated by acetyl--CoA.
Which coenzymes are used by the Pyruvate Dehydrogenase complex? A. NAD+, CoA, alpha-lipoic acids, and TPP B. FADH2, ATP, and GTP C. NADH, FAD, and H2O D. GTP, CoA, and Citrate E. TPP, CO2, and ADP
A. NAD+, CoA, alpha-lipoic acids, and TPP
Which statement describes the overall action of ETS complex I? A. NADH is oxidized; Coenzyme Q is reduced B. NADH is reduced; Coenzyme Q is oxidized C. NADH is reduced; Oxygen is oxidized NADH D. is oxidized; FAD is reduced E. Transports 12 H+
A. NADH is oxidized; Coenzyme Q is reduced
An in vitro experiment used the isotope 14C-acetyl-CoA to identify 14C-oxaloacetate (OAA) as the final product of the citrate cycle. Explain why 14C-OAA could not be found when the reaction lacked Pi? A. Pi is a required in the succinyl-CoA synthetase reaction, which was inhibited, so no 14C-OAA is made. B. Pi is required in the malate dehydrogenase reaction, which was inhibited, so no 14C-OAA is made. C. Succinyl-CoA synthetase requires ADP + Pi to form GMP, so without Pi, no 14C-OAA is made. D. The Pi is an activator of citrate lyase in the cytosol, so without Pi, so no 14C-OAA is made. E. Succinyl-CoA synthetase uses Pi to generate alpha-ketoglutarate, so no 14C-OAA is made.
A. Pi is a required in the succinyl-CoA synthetase reaction, which was inhibited, so no 14C-OAA is made.
What role do vitamins have in the pyruvate dehydrogenase reaction? Choose the FOUR correct answers. A. Vitamin B3 is a critical component of not only the PDH complex, but also the alpha-ketoglutarate dehydrogenase complex, an enzyme in the citrate cycle. B. Riboflavin is an electron carrier that functions in a redox reaction involving dihydrolipoamide. C. Thiamin pyrophosphate transfers a pair of electrons from E2 to E3, which in turn, oxidizes NAD+ to generate NADH + H+. D. Vitamins provide functional chemical groups in all three subunits of the PDH protein complex. E. One of the reasons why people get beriberi when their diets are lacking in vitamin B1 is that the PDH reaction becomes overstimulated and high levels of acetyl-CoA are toxic. F. Vitamin B5 functions as an acetate carrier using a high energy thioester bond formed in the E2 catalytic site. G. Most children in developed countries have defective PDH protein complexes and suffer from malnourishment because they eat too much Captain Crunch cereal and not enough broccoli, asparagus, and brown rice.
A. Vitamin B3 is a critical component of not only the PDH complex, but also the alpha-ketoglutarate dehydrogenase complex, an enzyme in the citrate cycle. B. Riboflavin is an electron carrier that functions in a redox reaction involving dihydrolipoamide. D. Vitamins provide functional chemical groups in all three subunits of the PDH protein complex. F. Vitamin B5 functions as an acetate carrier using a high energy thioester bond formed in the E2 catalytic site.
A new species of bacterium was isolated from hot springs inYellowstone in which the subunit stoichiometry of its ATP synthase complex isunusual compared to other organisms. It was found that there are 16 c ring subunits, 1 g subunit, 4 a subunits and 4 b subunits (the other subunits are present as well). Based on what is known about the structure and function of ATP synthase enzymes in other organisms, answer these three questions. a) How many H+ most likely flow through ATP synthase to generate 1 ATP? b) How many degrees of rotation by the g subunit occur for 1 ATP synthesized by the bacterium? c) Considering that 8 H+ are translocated per NADH oxidized by this bacterial electron transport system, and the species contains a similar phosphate translocase as mitochondria, what is the ATP currency exchange ratio in terms of moles ATP synthesized for every mole NADH that is oxidized? A. a) 4; b) 90o; c) 1.6 B. a) 6; b) 120o; c) 1.6 C. a) 4; b) 90o; c) 2.5 D. a) 4; b) 180o; c) 3.2 E. a) 8; b) 90o; c) 4.0
A. a) 4; b) 90o; c) 1.6
The poison compound 1080 converts fluoroacetate to fluorocitrate. Which enzyme in the citrate cycle is inhibited by this poison? A. aconitase B. citrate synthase C. isocitrate dehydrogenase D. -ketoglutaratedehydrogenase E. pyruvate decarboxylase
A. aconitase
The pyruvate dehydrogenase reaction is regulated by ________________. A. allosteric control and covalent modification B. pH and the protonation state of the active site C. pH and enzyme conformation D. product inhibition
A. allosteric control and covalent modification
After robust lipid breakdown by the cell, there could be an increase in the rate of Choose one or more: A. carbohydrate synthesis. B. photosynthesis. C. the citrate cycle. D. amino acid synthesis.
A. carbohydrate synthesis. C. the citrate cycle. D. amino acid synthesis.
Red blood cells lack mitochondria. Which of the following do they use to generate their ATP? A. glycolysis B. citrate cycle C. electron transport system D. oxidative phosphorylation E. ATP synthase
A. glycolysis
Concerning proton movement in mitochondria and chloroplasts, the __________ have a __________ H+ concentration. A. intramembrane space in mitochondria; high B. lumen in chloroplasts; low C. matrix in mitochondria; high D. stroma in chloroplasts; high
A. intramembrane space in mitochondria; high
Five coenzymes are needed for the pyruvate dehydrogenase (PDH) reaction. Name the three that are covalently linked to proteins in the PDH complex. A. lipoamide, TPP, FAD B. CoA, lipoamide, NAD+ C. TPP, NAD+, FAD D. TPP, CoA, lipoamide E. NAD+, FAD, CoA
A. lipoamide, TPP, FAD
A good reason to refer to the metabolic cycle discovered by Hans Krebs as the CITRATE cycle is ________________. A. the three carboxylate groups are deprotonated under physiological conditions, and therefore do not function as acids. B. that other names such as the Krebs cycle and the TCA cycle are confusing. C. the enzyme in the first reaction is called citrate synthetase, so it just makes sense to call the metabolic cycle the citrate cycle. D. the pKa values of the three carboxylate groups are all higher than pH 7, and therefore the COO- groups will be protonated under physiological conditions.
A. the three carboxylate groups are deprotonated under physiological conditions, and therefore do not function as acids.
If acetyl-CoA is not metabolized by the citrate cycle, the molecule in the cell A. undergoes fatty acid metabolism. B. is transported across the cell membrane. C. is used to synthesize amino acids. D. is used during glycolysis. E. is used to produce oxaloacetate
A. undergoes fatty acid metabolism.
In 2 turns of the citrate cycle, (a) how many electrons are transferred to NAD+, (b) how many CO2 are produced, and (c) how manyGTP are generated? A. (a) 18 electrons, (b) 4 CO2, (c) 3 GTP B. (a) 12 electrons, (b) 4 CO2, (c) 2 GTP C. (a) 24 electrons, (b) 6 CO2, (c) 3 GTP D. (a) 8 electrons, (b) 2 CO2, (c) 1 GTP E. (a) 9 electrons, (b) 6 CO2, (c) 4 GTP
B. (a) 12 electrons, (b) 4 CO2, (c) 2 GTP
Choose the correct word for each pair of underlined. The citrate cycle is considered the hub (1) / stator (2) of metabolism for three reasons,1) it generates the bulk of NADH (3) / NAD+ (4) and FAD (5) / FADH2 (6) used inoxidative phosphorylation, the process that generates 30 GTP (7) / ATP (8) perglucose, 2) it oxidizes a variety of metabolic fuels (9) / cations (10) from differentsources, and 3) it provides metabolites required for the biosynthesis of amino (11) / fatty (12) acids.
B. 1, 3, 6, 8, 9, 11
Considering that 22.4 kJ/mole is required to transport 1 H+ across the mitochondrial membrane, how much energy is available for proton translocation from the oxidation of FADH2 at Complex II? A. 22.4 kJ/mol B. 134 kJ/mol C. 224 kJ/mol D. 112 kJ/mol E. 268 kJ/mol
B. 134 kJ/mol
In two turns of the citrate cycle originating from oxidation of 2 moles of acetyl-CoA, how many electrons are transferred from the citrate cycle intermediates to NAD+ and FAD? A. 4 B. 16 C. 12 D. 8
B. 16
Which one of the statements below best describes the mechanism of proton translocation by the Electron Transport System using a redox loop mechanism exemplified by the Q cycle? A. When the e- binds to cytochrome c, it results in dissociation of cytochrome c from complex II, which stimulates release of H+ from complex IV, and thereby translocates protons and electrons separately. B. A redox reaction separating protons and electrons within complex III of the electron transport system, with the protons translocated to the inter-membrane space and the electrons used to reduce Q. C. A redox reaction results in a H+ and e- that are separated within the electron transport system and deposited on opposite sides of the outer mitochondrial membrane, with protons on the negative side. D. The flow of coenzyme Q between complex I and complex II alters membrane fluidity, which makes the membrane briefly permeable to protons; this reaction can be activated by ingesting CoQ10 vitamins. E. The redox loop that forms between Complex I and Complex III in which CoQ10 serves as a one electron carrier between the complexes with Fe2+/Fe3+ cytochrome heme in the central pocket of the protein.
B. A redox reaction separating protons and electrons within complex III of the electron transport system, with the protons translocated to the inter-membrane space and the electrons used to reduce Q.
Why is it more accurate to call the pathway that converts acetyl-CoA to CoA + 2 CO2 the citrate cycle, rather than the tricarboxylic acid cycle (TCA), or simply the citric acid cycle? A. Because Krebs cycle, TCA, and citric acid cycle are three different metabolic pathways. B. Because the primary product of reaction 1 in cells is citrate, which is a base not an acid at pH 7. C. Because tricarboxylic acid (TCA) could also be confused with trichloroacetic acid, which is confusing. D. Because Edwin Krebs thought that the carboxyl groups of citric acid had a pKa of ~9 instead of ~5. E. Because the primary product of reaction 1 in cells is isocitrate, which is a base not an acid at pH 4.
B. Because the primary product of reaction 1 in cells is citrate, which is a base not an acid at pH 7.
Which of the following is a negative effector for pyruvate dehydrogenase kinase? A. ATP B. Ca2+ C. Acetyl-CoA D. NADH
B. Ca2+
Which statement below bests describes the Chemiosmotic Theory proposed by Peter Mitchell? A. An electrical current is analogous to a proton current with the exception that capacitors are resistors. B. Conversion of redox energy or light energy into potential energy as an electrochemical proton gradient. C. A theory that assumes hydrogen bond strength between H and O is greater than between N and H. D. The process by which phosphoryl transfer energy is converted to redox energy and a Na+ gradient. E. The idea that X~P is a high energy phosphate intermediate that results in the direct formation of ATP.
B. Conversion of redox energy or light energy into potential energy as an electrochemical proton gradient.
What is the biochemical mechanism by which ingesting 2,4-dinitrophenol (DNP) results in rapid weight loss by increased rates of metabolic flux through the fatty acid degradation pathway? A. DNP uncouples electron transport from ATP synthesis and the body stores excess fatty acids at a high rate to increase the energy charge. B. DNP uncouples electron transport from ATP synthesis and the body degrades stored fatty acids at a high rate to increase the energy charge. C. DNP increases the efficiency of oxidative phosphorylation, which leads to high rates of fatty acid degradation to decrease energy charge. D. DNP is an inhibitor of ATP synthase, which increases NADH oxidation by Complex I in the electron transport system, the result is fatty acid catabolism. E. DNP transports protons from the mitochondrial matrix to the intermembrane space, which increases rates of fatty acid degradation leading to weight loss.
B. DNP uncouples electron transport from ATP synthesis and the body degrades stored fatty acids at a high rate to increase the energy charge.
A mutation in pyruvate carboxylase that blocks its ability to be regulated by acetyl-CoA results in lower rates of energy conversion via the citrate cycle. What is the reason for this; choose the most correct answer? A. If PC is not activated by excess acetyl-CoA, then the α-ketoglutarate is not effectively oxidized to succinyl-CoA resulting in a reduction of NADH. B. If PC is not activated by excess acetyl-CoA, then oxaloacetate is limiting so the rate oxidation of acetyl-CoA is not maintained at the maximum rate and energy conversion decreases. C. If PC is not activated by excess acetyl-CoA, then citrate does not accumulate in the mitochondrial matrix and inhibit the citrate synthase reaction. D. If PC is not activated by excess acetyl-CoA, then the ETS becomes chemically uncoupled is the proton gradient is dissipated leading to a reduction in energy conversion. E. If PC is not activated by excess acetyl-CoA, then ATP cannot translocate across the mitochondrial membrane leading to a reduction in energy conversion.
B. If PC is not activated by excess acetyl-CoA, then oxaloacetate is limiting so the rate oxidation of acetyl-CoA is not maintained at the maximum rate and energy conversion decreases.
You are finally getting your experiment to work now and have accumulated quite a bit of ATP in the surrounding solution. You decide to test the hypothesis that the ATP synthase can work in reverse, breaking ATP down to ADP and Pi instead of synthesizing it. How might you need to modify your experiment to test your hypothesis? A. Raise the pH of the surrounding solution. B. Lower the pH of the surrounding solution. C. Increase the [ATP] in the surrounding solution. D. Add a competitive inhibitor of bacteriorhodopsin
B. Lower the pH of the surrounding solution.
Oxaloacetate is transported both into and out of the mitochondrial matrix via which of the following molecules? A. α-ketoglutarate B. Malate C. Citrate D. Succinyl-CoA
B. Malate
The pyruvate dehydrogenase (PDH) complex catalyzes an essentially irreversible reaction that links glycolysis to the citrate cycle and fatty acid metabolism. Thus, PDH regulation is critical to controlling the metabolic flux in response to the available nutrients in the body. Pyruvate dehydrogenase kinase (PDK) is the enzyme that regulates PDH. What does PDK do and how is it allosterically regulated? A. PDK is an enzyme that converts pyruvate to acetyl-CoA that is activated by NADH, acetyl-CoA and ATP and inhibited by NAD+, CoA and ADP. B. PDK is an enzyme that phosphorylates PDH, which inactivates it. PDK is activated by NADH, acetyl-CoA and ATP while it is inhibited by NAD+, CoA and ADP. C.PDK is an enzyme that dephosphorylates PDH that is activated by Ca2+. D. PDK is an enzyme that converts pyruvate to acetyl-CoA that is activated by NAD+,CoA and ADP and inhibited by NADH, acetyl-CoA and ATP. E. PDK is an enzyme that phosphorylates PDH, which inactivates it. PDK is activated by NAD+, CoA and ADP while it is inhibited by NADH, acetyl-CoA and ATP.
B. PDK is an enzyme that phosphorylates PDH, which inactivates it. PDK is activated by NADH, acetyl-CoA and ATP while it is inhibited by NAD+, CoA and ADP.
Which statement below is the most correct concerning the transport of ATP, ADP, and Pi across the mitochondrial inner membrane? A. Transport of Pi across the membrane by the phosphate translocase is not electrically neutral. B. Phosphate translocase functions as a symporter when transporting Pi and H+. C. The transport of ATP and ADP by the mitochondrial ATP/ADP translocase is electrically neutral. D. Phosphate translocase functions as an antiporter when transporting Pi and ADP. E. ATP diffuses across the inner mitochondrial membrane, but ADP requires the translocase.
B. Phosphate translocase functions as a symporter when transporting Pi and H+.
Choose the ONE best answer explaining how oxaloacetate and acetyl-CoA levels are balanced to maximize flux through the citrate cycle when energy charge in the cell is low. A. Acetyl-CoA can be produced by the degradation of fat, and therefore, it is advantageous to stimulate ketogenesis by increasing the amount of oxaloacetate through activation of the isocitrate dehydrogenase reaction. B. Pyruvate dehydrogenase is activated by CoA but inhibited by its product acetyl-CoA, whereas pyruvate carboxylase is activated by acetyl-CoA to produce more oxaloacetate for the citrate synthase reaction. C. Pyruvate carboxylase and pyruvate dehydrogenase both require thiamin pyrophosphate (TPP), which facilitates coordinate regulation of the two enzymatic reactions and increased citrate cycle flux. D. The best way to balance the input of carbon into the citrate cycle is to regulate the production of citrate using vitamins like panthothenic acid, which is the cause of beriberi in southeast Asia.
B. Pyruvate dehydrogenase is activated by CoA but inhibited by its product acetyl-CoA, whereas pyruvate carboxylase is activated by acetyl-CoA to produce more oxaloacetate for the citrate synthase reaction.
How would a high NADH to NAD+ ratio be expected to affect the pyruvate dehydrogenase reaction? A. The pyruvate dehydrogenase phosphatase-1 enzyme would increase, resulting in pyruvate dehydrogenase activation at an accelerated rate. B. The E1 subunit is phosphorylated by pyruvate dehydrogenase kinase, and the catalytic activity of pyruvate dehydrogenase decreases. C. The pyruvate dehydrogenase kinase enzyme activity would increase, resulting in an increase in pyruvate dehydrogenase activity. D. The last step of the pyruvate dehydrogenase reaction is stimulated, resulting in an increase in activity
B. The E1 subunit is phosphorylated by pyruvate dehydrogenase kinase, and the catalytic activity of pyruvate dehydrogenase decreases.
In the citrate cycle, the enzyme succinate dehydrogenase catalyzes a reversible reaction usingFAD/FADH2 as an oxidizing/reducing conjugate pair. Which of the following statements explains how the redox component contributes to the reversibility of this reaction? A. FAD can be reduced by sequential addition of one hydrogen at a time. B. The change in biochemical standard reduction potential is small. C. FAD has no reduction potential when it is enzyme-bound. D. FAD/FADH2 component is covalently bound to the enzyme. E. The redox reaction uses ATP hydrolysis to drive the reverse reaction.
B. The change in biochemical standard reduction potential is small.
In the citric acid cycle, the enzyme succinate dehydrogenase catalyzes a reversible reaction using FAD/FADH2 as an oxidizing/reducing agent. Which of the following statements best explains how the redox component of this reaction contributes to the reaction's ability to be reversible under cellular conditions? A. FAD/FADH2 is covalently bound to succinate dehydrogenase. B. The change in the biochemical standard reduction potential is small. C. FAD has no reduction potential when it is enzyme-bound. D. FAD can be reduced by the sequential addition of one hydrogen at a time.
B. The change in the biochemical standard reduction potential is small.
Regeneration of NAD+ and FAD inside the mitochondrial matrix is required because_____________. A. They transport pyruvate through the matrix. B. They maintain flux through the citrate cycle. C. They produce GDP through the citrate cycle. D. Anabolic reactions generally require them. E. They are required for glycolysis.
B. They maintain flux through the citrate cycle.
To make high levels of citrate to produce commercial grade citric acid, Pfizer modified culture conditions and used a special strain of Aspergillus niger to maximize fermentation. What two processes need to be inhibited in order to ensure the rate of citrate secretion exceeds citrate catabolism? A. pyruvate carboxylase reaction and ATP production B. citrate cycle flux and the citrate lyase reaction C. glucose import and citrate synthase reaction D. citrate cycle flux and the fumarase reaction E. the glycolytic pathway and the pyruvate carboxylase reaction
B. citrate cycle flux and the citrate lyase reaction
In which of the following metabolic conversions is ATP "consumed" during glycolysis? A. 1,3-Bisphosphoglycerate --> 3-phosphoglycerate B. fructose-6-phosphate --> fructose-1,6-bisphosphate C. Dihydroxyacetone --> glyceraldehyde-3-phosphate D. glucose-6-phosphate --> fructose-6-phosphate E. 2-phosphoglycerate --> phosphophenolpyruvate
B. fructose-6-phosphate --> fructose-1,6-bisphosphate
Coenzyme A is derived from which of the following vitamins? A. thiamine B. pantothenic acid C. riboflavin D. niacin E. ATP
B. pantothenic acid
Which statement is correct for Glycolysis? A. We have 1 ATP investment stages and 4 earning states B. 1 Glucose molecule makes 4 pyruvates C. 1 Glucose molecule makes 2 pyruvates D. The most important production center for ATP production E. Is never regulated
C. 1 Glucose molecule makes 2 pyruvates
How many ATPs are produced in muscle cells? A. 32 B. 28 C. 30 D. 64 E. 2
C. 30
Given that metabolic flux through the Citrate Cycle is regulated by energy charge and by NADH and citrate concentrations, which statement below most accurately describes regulatory effects of the listed metabolites on flux through the Citrate Cycle? A. ATP, and NADH are allosteric activators, whereas ADP, citrate, and AMP are allosteric inhibitors. B. AMP, citrate, and NAD+ are allosteric inhibitors, whereas ATP and AMP are allosteric activators. C. ATP, citrate, and NADH are allosteric inhibitors, whereas ADP and AMP are allosteric activators. D. ADP and ATP are allosteric activators, whereas AMP, citrate, and NADH are allosteric inhibitors. E. None of these answers are correct.
C. ATP, citrate, and NADH are allosteric inhibitors, whereas ADP and AMP are allosteric activators.
As part of the troubleshooting process, you decide to investigate whether a proton gradient is present across the artificial membranes in your test tube. When comparing proton concentrations and membrane potentials (Δψ), which of the following would be evidence of a properly formed proton gradient? A. Inside the vesicle we have a lower [H+] and a more positive Δψ compared to the outside of the vesicle. B. Inside the vesicle we have a lower [H+] and a more negative Δψ compared to the outside of the vesicle. C. Inside the vesicle we have a higher [H+] and a more positive membrane potential, Δψ, compared to the outside of the vesicle. D. Inside the vesicle we have a higher [H+] and a more negative Δψ compared to the outside of the vesicle.
C. Inside the vesicle we have a higher [H+] and a more positive membrane potential, Δψ, compared to the outside of the vesicle.
How does phosphoglycerate kinase make glycolysis energy neutral at this step? A. It results in a reaction at equilibrium B. It results in a reaction is endergonic C. It produces 2 ATP along with 3-phosphoglycerate D. It results in a reaction at equilibrium E. It uses ATP to produce 3-phosphoglycerate
C. It produces 2 ATP along with 3-phosphoglycerate
Pyruvate dehydrogenase (PDH) activity is controlled by phosphorylation such that PDH activity is decreased (T state) when it is phosphorylated. What enzyme increases PDH activity (R state)? A. PDH kinase B. Dihydrolipoyltransferase C. PDH phosphatase-1 D. Pantothenate kinase E. Hexokinase
C. PDH phosphatase-1
Which mitochondrial protein exchanges inorganic phosphate for protons across the membrane? A. Porin protein B. Proton exchanger C. Phosphate translocase D. ATP/ADP translocase E. GLUT4
C. Phosphate translocase
The disease beriberi is caused by a nutritional deficiency in vitamin B1 (thiamin). What key mitochondrial enzyme uses thiamin as a coenzyme in a reaction that generates acetyl-CoA, CO2, and NADH + H+ as products; and why is this condition rare in developed countries? A. Citrate synthase; beriberi is rare because thiamin can be obtained from drinking water. B. Malate dehydrogenase; beriberi is rare because other vitamins can replace thiamin. C. Pyruvate dehydrogenase; beriberi is rare because many common foods are vitamin fortified. D. Fumarase; beriberi is rare because DNA contains large amounts of thiamin paired with adenine. E. Pyruvate dehydrogenase; beriberi is rare because developed countries have blueberries in their diets.
C. Pyruvate dehydrogenase; beriberi is rare because many common foods are vitamin fortified.
The NADH that is produced by glycolysis under anaerobic conditions is regenerated to NAD+ by the conversion of A. Lactate → pyruvate B. glucose → glucose-6-phosphate. C. Pyruvate → lactate D. Phosphophenal pyruvate → pyruvate. E. Ethanol → CO2.
C. Pyruvate → lactate
Which of the following is a net result from the electron transport system? A. Reduction of NAD+ B. ATP hydrolysis C. Reduction of molecular oxygen D. Reduction of FAD
C. Reduction of molecular oxygen
Which enzyme is used in the citrate cycle and the ETS? A. Citrate synthase B. Isocitrate dehydrogenase C. Succinate dehydrogenase D. Fumarase E. Malate dehydrogenase
C. Succinate dehydrogenase
Select the one statement below best describing structure/function of the ATP synthase complex. A. The ATP synthase can only run in one direction in vitro, namely in the direction to synthesize ATP. B. Rotation of the c ring in the membrane is driven by protonation/deprotonation of a proline residue in the c subunit, and when it is protonated, it is now neutral and easily enters the hydrophobic membrane. C. The gamma subunit is asymmetric, therefore as it rotates in 120o steps in response to proton flow through Fo, it makes 3 different contacts resulting in 3 different conformations of the beta subunits. D. Proton flow through the Fo subunit causes rotation of the entire F1 subunit, including the catalytic headpiece which alters the affinity of the beta subunits for ATP and releasing the newly synthesized ATP. E. ATP synthase consists of three mechanical parts, all of which rotate using kinetic energy from redox.
C. The gamma subunit is asymmetric, therefore as it rotates in 120o steps in response to proton flow through Fo, it makes 3 different contacts resulting in 3 different conformations of the beta subunits.
Beriberi results from a deficiency in which of the following vitamins? A. Riboflavin B. Niacin C. Thiamine D. Pantothenic acid
C. Thiamine
Which of the following statements concerning ATP, ADP, and Pi transport across the inner mitochondrial membrane is correct? A. Phosphate translocase only acts as an antiporter in transporting H2PO4 and H+. B. The transport of ATP and ADP via the mitochondrial ATP/ADP translocase is electrically neutral. C. Transport of H2PO4 via phosphate translocase is electrically neutral. D. Phosphate translocase only acts as a symporter in transporting H2PO4 and OH-.
C. Transport of H2PO4 via phosphate translocase is electrically neutral.
What type of transport protein is the mitochondrial ATP/ADP translocase? A. a symporter B. an active transporter C. an antiporter D. a diffusible active transporter E. a uniporter
C. an antiporter
If blood glucose levels are highly elevated, glucokinase in the pancreas becomes very active. This results in a signaling pathway that ultimately results in: A. the inhibition of glycolysis B. the production of more hexokinase C. the release of insulin D. the inhibition of the citrate cycle E. stimulates the production of fat
C. the release of insulin
If acetyl-CoA is not metabolized by the citrate cycle, its most likely metabolic fate is___________. A. used to synthesize H2S. B. transported across the cell membrane. C. used to synthesize fatty acids. D. used to synthesize amino acids. E. used during glycolysis.
C. used to synthesize fatty acids.
Answer these four questions regarding the ATP currency exchange ratio. a) How many protons are required to be transported into the mitochondrial matrix for every ATP that is synthesized and exported to the cytosol? b) How many protons are transported across the inner mitochondrial membrane for every NADH that is oxidized by Complex I the electron transport system? c) How many protons are transported across the inner mitochondrial membrane for every FADH2 that is oxidized by Complex II in the electron transport system? d) What explains the difference between number of ATP synthesized per NADH that is oxidized by the electron transport system compared to the number of ATP synthesized per FADH2 that is oxidized? A. (a) 4 protons, (b) 12 protons, (c) 6 protons, (d) 12/4 = 3 ATP/NADH and 6/3 = 2 ATP/ FADH2 B. (a) 4 protons, (b) 10 protons, (c) 8 protons, (d) 10/4 = 2.5 ATP/ FADH2 and 8/4 = 2 ATP/NADH C. (a) 4 protons, (b) 8 protons, (c) 6 protons, (d) 8/4 = 2 ATP/NADH and 6/4 = 1.5 ATP/ FADH2 D. (a) 4 protons, (b) 10 protons, (c) 6 protons, (d) 10/4 = 2.5 ATP/NADH and 6/4 = 1.5 ATP/FADH2 E. (a) 6 protons, (b) 10 protons, (c) 9 protons, (d) 6/4 = 1.5 ATP/NADH and 9/3 = 3 ATP/FADH2
D. (a) 4 protons, (b) 10 protons, (c) 6 protons, (d) 10/4 = 2.5 ATP/NADH and 6/4 = 1.5 ATP/FADH2
When cytochrome c diffuses away from Complex III it contains Fe2+ in the reduced form that is oxidized to Fe3+ following a redox reaction between cytochrome c and Complex IV. One of the cytochromes within Complex IV is called cytochrome a3, which is reduced as a result of cytochrome c interactions with electron acceptors in Complex IV. These redox reactions within Complex IV result in oxidized cytochrome a3 (Fe3+) becoming reduced cytochrome a3 (Fe2+). Based on the standard reduction potentials for cytochrome c (+0.23 V) and cytochrome a3 (+0.38 V), what is the DGo' of the combined redox reaction shown below? Cyto c (Fe2+) + Cyto a3 (Fe3+) --> Cyto c (Fe3+) + Cyto a3 (Fe2+) A. +14.5 kJ/mol B. -29.0 kJ/mol C. -11.6 kJ/mol D. -14.5 kJ/mol E. -7.3 kJ/mol
D. -14.5 kJ/mol
Choose the TWO correct statements describing the citrate cycle. A. ADP inhibits α-ketoglutarate dehydrogenase B. All enzymes of the citric acid cycle are found soluble and free in the mitochondrial matrix C. Acetyl CoA can increase the pool of citric acid cycle intermediates D. ATP is an indirect product of the citric acid cycle E. The pool of mitochondrial oxaloacetate can be increased by pyruvate F. Fatty acids can increase the pool of citric acid cycle intermediates
D. ATP is an indirect product of the citric acid cycle E. The pool of mitochondrial oxaloacetate can be increased by pyruvate
The coenzyme used by pyruvate carboxylase is: A. FAD B. TPP C. NAD+ D. Biotin
D. Biotin
Which molecular component of the electron transport system diffuses throughout the inner mitochondrial membrane to carry electrons between complexes in the electron transport system? A. Plastoquinone B. FADH2 C. NAD+ D. Coenzyme Q E. Cytochrome c
D. Coenzyme Q
Which of the following diffuses throughout the inner mitochondrial membrane to carry electrons between complexes in the electron transport system? A. FAD B. Cytochrome c C. NAD+ D. Coenzyme Q
D. Coenzyme Q
In oxidative phosphorylation, chemiosmosis involves the outward pumping of H+ across the mitochondrial matrix. Which protein complexes in the electron transport system directly contribute to this process? A. Complexes I, II B. Complexes III, IV C. Complexes I, II, III D. Complexes I, III, IV E. Complexes I, IV
D. Complexes I, III, IV
Which of the following is an inhibitor of complex IV? A. Rotenone B. Antimycin C. Oligomycin D. Cyanide
D. Cyanide
The purpose of the first three steps in the pyruvate dehydrogenase reaction is to__________. A. Regenerate the oxidized form of lipoamide B. Form NADH C. Transfer electrons D. Form acetyl-CoA
D. Form acetyl-CoA
Under anaerobic conditions, what is an important source of ATP in the cells? A. Oxidative phosphorylation B. Citrate Cycle C. Malate-Aspartate shuttle D. Glycolysis E. Pyruvate decarboxylase
D. Glycolysis
What is a reasonable explanation for why the presence of cytosolic cytochrome c (Cyt c) is an initiating signal for cell death (apoptosis) in eukaryotic cells? A. High levels of Cyt c in the cytosol indicate that mitochondria are generating lots of heat, so death is best. B. Low levels of Cyt c in the cytosol are expected, it is high levels in the matrix that are bad, so death is best C. High levels of Cyt c in cytosol are normal, apoptosis is always initiated by TNF alpha, so death is best. D. High levels of Cyt c in the cytosol signal that mitochondria are not functioning properly, so death isbest. E. None of these answers are correct.
D. High levels of Cyt c in the cytosol signal that mitochondria are not functioning properly, so death is best.
Which statement best describes the biochemical function of pyruvate carboxylase in regulating metabolic flux through the citrate cycle? A. In the presence of high levels of CoA, pyruvate carboxylase converts malate to oxaloacetate. B. In the presence of low levels of acetyl-CoA, pyruvate carboxylase converts pyruvate to oxaloacetate. C. In the presence of low levels of CoA, pyruvate carboxylase converts pyruvate to oxaloacetate. D. In the presence of high levels of acetyl-CoA, pyruvate carboxylase converts pyruvate to oxaloacetate. E. Pyruvate carboxylase is the same as pyruvate dehydrogenase and converts pyruvate to acetyl-CoA.
D. In the presence of high levels of acetyl-CoA, pyruvate carboxylase converts pyruvate to oxaloacetate.
The Citrate Cycle is an amphibolic pathway because A. It functions in catabolic pathways B. It reduces Acetyl CoA C. It produces fatty acids D. It serves in catabolic and anabolic pathways E. There are reactions that replenish key cycle intermediates
D. It serves in catabolic and anabolic pathways
Explain why a mutation in pyruvate carboxylase that blocks its ability to be regulated by acetyl- CoA results in lower rates of energy conversion via the Citrate Cycle. A. Under actual conditions the ratio of [OAA]•[NADH] is 100,000 times higher than that of the substrates. B. Malate is used in many, many other reactions in the cytosol and often used to generate acetyl-CoA. C. Oxidation of fats requires sufficient levels of acetyl-CoA to maintain flux through the glycolytic pathway. D. Oxaloacetate becomes limiting, reducing the rate of acetyl-CoA oxidation, which inhibits citrate cycle flux. E. In the presence of high levels of CoA, pyruvate carboxylase will be stimulated and generate malate.
D. Oxaloacetate becomes limiting, reducing the rate of acetyl-CoA oxidation, which inhibits citrate cycle flux.
What would happen if mitochondria were treated with a proton gradient uncoupler, such as 2,4-dinitrophenol? A. Electron transfer would stop B. Reducing equivalents, in the form of NADH, would no longer be consumed C. Complex 1 would become reduced, and complexes III and IV would become oxidized D. Protons would be pumped but no ATP would be synthesized
D. Protons would be pumped but no ATP would be synthesized
Although both pyruvate dehydrogenase and glyceraldehyde 3-phosphate dehydrogenase use NAD+ as their electron acceptor, the two enzymes do not compete for the same cellular NAD pool because ___________. A. NAD+/NADH remains tightly bound to each enzyme, so the NAD pools are not shared. B. The pyruvate dehydrogenase reaction also uses FAD so the NAD is from a different pool that is associated with FADH2. C. NAD+/NADH are only used once before being degraded, so they are not regenerated for subsequent rounds. D. Pyruvate dehydrogenase is located in the mitochondrion, and glyceraldehyde 3-phosphate dehydrogenase in the cytosol. E. These enzymes don't need NAD+ as their electron acceptors.
D. Pyruvate dehydrogenase is located in the mitochondrion, and glyceraldehyde 3-phosphate dehydrogenase in the cytosol.
Which of the following is responsible for the production of GTP in the citrate cycle? A. Succinate dehydrogenase B. Isocitrate dehydrogenase C. Malate dehydrogenase D. Succinyl-CoA synthetase
D. Succinyl-CoA synthetase
ATP synthase: Which is correct? A. F0 encodes all catalytic activity B. The beta subunits always bind ATP and the alpha subunits release it C. The ATP synthase needs electrons to rotate the catalytic part D. The ATP Synthase is also an ATP hydrolase by changing the direction of movement E. It is the largest monomeric protein in humans
D. The ATP Synthase is also an ATP hydrolase by changing the direction of movement
How would an increased level of acetyl-CoA be expected to affect the pyruvate dehydrogenase reaction? A. The pyruvate dehydrogenase phosphatase-1 enzyme would increase, resulting in pyruvate dehydrogenase activation at an accelerated rate. B. The last step of the pyruvate dehydrogenase reaction would be blocked, resulting in a decrease in activity. C. The E1 subunit would be phosphorylated by pyruvate dehydrogenase kinase, and the catalytic activity of pyruvate dehydrogenase would increase. D. The pyruvate dehydrogenase kinase enzyme activity would increase, resulting in an inhibition of pyruvate dehydrogenase activity.
D. The pyruvate dehydrogenase kinase enzyme activity would increase, resulting in an inhibition of pyruvate dehydrogenase activity.
How would an increase in Ca2+ be expected to affect the pyruvate dehydrogenase reaction? A. The pyruvate dehydrogenase kinase enzyme activity would increase, resulting in an inhibition of pyruvate dehydrogenase activity. B. The last step of the pyruvate dehydrogenase reaction is blocked, resulting in a decrease in activity. C. The E1 subunit is phosphorylated by pyruvate dehydrogenase kinase, and the catalytic activity of pyruvate dehydrogenase decreases. D. The pyruvate dehydrogenase phosphatase-1 enzyme would increase, resulting in pyruvate dehydrogenase activation at an accelerated rate. E. no effect.
D. The pyruvate dehydrogenase phosphatase-1 enzyme would increase, resulting in pyruvate dehydrogenase activation at an accelerated rate.
The citrate cycle is used to generate NADH and FADH2 molecules (along with ATP by substrate level phosphorylation). If these cofactors are being reduced during the citrate cycle, what is happening to the corresponding intermediates (i.e., isocitrate, α-ketoglutarate, succinate, malate) during the citrate cycle? A. They are phosphorylated. B. They are reduced. C. They are isomerized. D. They are oxidized. E. They generate ATP.
D. They are oxidized.
In linked metabolic pathways, the oxidants in subsequent reactions must A. result in negative ∆E°' values at each reaction step. B. result in positive ∆G°' values at each reaction step. C. have progressively lower standard reduction potentials. D. have progressively higher standard reduction potentials. E. always reduce NAD+.
D. have progressively higher standard reduction potentials.
The reaction catalyzed by succinyl-CoA synthetase is a reversible reaction. What would be the first step in this mechanism moving in the direction toward the formation of succinyl-CoA, GDP, and Pi from succinate, GTP, and CoA? A. nucleophilic attack by γ-phosphate on GTP to form phosphosuccinate B. nucleophilic attack to form succinyl-CoA C. nucleophilic attack by γ-phosphate on GTP to form phosphohistidine D. reaction initiated by histidine lone pair to form phosphohistidine
D. reaction initiated by histidine lone pair to form phosphohistidine
A desert plant was shown to have a differential pH gradient (DpH) across thechloroplast thylakoid membrane of 3.5 pH units relative to the stroma. What is the DG totransport 1 H+ across the thylakoid membrane from the stroma at 30oC given that the thylakoid membrane potential was below the level of detection and effectively 0 V? A. +3.2 kJ/mol B. -20.3 kJ/mol C. +6.4 kJ/mol D. -8.8 kJ/mol E. +20.3 kJ/mol
E. +20.3 kJ/mol
Identify the correct order of electron transfers in the electron transport system starting with the mitochondrial enzyme glycerol-3P dehydrogenase (GPDH) and ending with reduction of 1⁄2 O2. A. GPDH-->Coenzyme Q-->Complex II-->Complex III-->1⁄2 O2 B. GPDH-->Complex II-->Complex III-->Coenzyme Q-->1⁄2 O2 C. GPDH-->Complex I-->Coenzyme Q-->Complex IV-->1⁄2 O2 D. GPDH-->Complex II-->Complex III-->Complex IV-->1⁄2 O2 E. GPDH-->Coenzyme Q-->Complex III-->Complex IV-->1⁄2 O2
E. GPDH-->Coenzyme Q-->Complex III-->Complex IV-->1⁄2 O2
Pellagra, a niacin deficiency, was found in residents of Village A, but not in Village B. It was found that Village A prepares corn by boiling it in water to make porridge. However, in Village B, the corn is soaked in mineral lime (calcium hydroxide) before cooking it over an open flame using a flat iron skillet in the form of tortillas. Why do residents of Village A have pellagra, but not residents of Village B? A. In Village B, the residents eat lots of tomatoes, which has high levels of lipoic acid to activate niacin. B. In Village A, niacin is bound tightly to corn and released when boiled in water, but too dilute to work. C. In Village B, niacin is released from yellow corn, which is very different than white corn in Village A. D. In Village A, niacin is oxidized and degraded by treatment with cold water which makes it toxic. E. In Village B, niacin is released by alkali treatment and high heat and converted to NAD+/NADH.
E. In Village B, niacin is released by alkali treatment and high heat and converted to NAD+/NADH.
What explains the ∆∆G value of ~0 kJ/mol for the malate dehydrogenase reaction in the Citrate Cycle considering that the ∆∆Go' value for this reaction is a very large positive value? A. Under actual conditions the ratio of [OAA]•[NADH] is 100,000 times higher than that of the substrates. B. Malate is used in many, many other reactions in the cytosol and never really builds up substantially. C. Oxaloacetate is used for the malate--aspartate shuttle as its primary metabolic fate in the cell. D. The ∆∆G value for this reaction is very large, and the ∆∆Go' value is ~0 kJ/mol, so it must work well. E. None of these answers are correct.
E. None of these answers are correct.
The disease beriberi is caused by a nutritional deficiency in vitamin B1 (thiamin). What key mitochondrial enzyme uses thiamin as a coenzyme in a reaction that generates acetyl-CoA, CO2, and NADH + H+ as products; and why is this condition rare in developed countries? A. Malate dehydrogenase; beriberi is rare because other vitamins can replace thiamin. B. Citrate synthase; beriberi is rare because thiamin can be obtained from drinking water. C. Fumarase; beriberi is rare because DNA contains large amounts of thiamin paired with adenine. D. Alpha-ketoglutarate dehydrogenase; beriberi is rare because most people eat berries for their oxidants. E. Pyruvate dehydrogenase; beriberi is rare because many common foods are vitamin-fortified.
E. Pyruvate dehydrogenase; beriberi is rare because many common foods are vitamin-fortified.
(T/F) The primary function of the citrate cycle is to oxidize pyruvate.
FALSE
(T/F) The two enzymes in the citrate cycle that are affected by arsenic poisoning are pyruvate dehydrogenase and malate dehydrogenase.
FALSE
Which metal in cytochrome c enables electron transport? Copper Zinc No metal, it is oxygen Iron Magnesium
Iron
Which two molecules function as electron acceptors in the citrate cycle? NADH, FADH2 GTP, ATP GDP, ADP NAD+, FAD O2, H2O
NAD+, FAD
Which citrate cycle metabolite listed below is an inhibitor of the pyruvate dehydrogenase reaction? NAD+ FAD H2O NADH
NADH
(T/F) Citrate cycle reactions in eukaryotic cells take place in the mitochondria.
TRUE
(T/F) NAD+ and FAD function as electron acceptors in the citrate cycle.
TRUE
(T/F) The pyruvate dehydrogenase reaction is regulated by allostery and covalent modification (phosphorylation)
TRUE
Which subunit of ATP synthase contains the active site of the protein? a. The c10 ring b. The β subunit c. The γ subunit d. The δ subunit e. The ε subunit
b. The β subunit
Which mitochondrial protein exchanges inorganic phosphate for protons across the membrane? a. Porin protein b. Proton exchanger c. Phosphate translocase d. ATP/ADP translocase e. GLUT4
c. Phosphate translocase
