Mcq_mini3_(4)[1] Tca Cycle And Oxidative Phosphorylation
Questions and Answers
- 1.
A deficiency of thiamine in glucose metabolism wouId resuIt in:
- A.
A decrease in cellular concentrations of pyruvate, alanine and lactate.
- B.
Enhanced activity of the pyruvate dehydrogenase complex.
- C.
A decrease in the concentration of alpha-ketoglutarate
- D.
Reduced activity of lactase dehydrogenase
- E.
Reduced levels of NADH for Oxidative phospharylation.
Correct Answer
E. Reduced levels of NADH for Oxidative phospharylation.Explanation
A deficiency of thiamine in glucose metabolism would result in reduced levels of NADH for oxidative phosphorylation. Thiamine is a cofactor for enzymes involved in the conversion of pyruvate to acetyl-CoA, which is a crucial step in the production of NADH. Without sufficient thiamine, this conversion is impaired, leading to a decrease in the levels of NADH available for oxidative phosphorylation, which is the final step in cellular respiration. This reduction in NADH levels can negatively impact the production of ATP, the energy currency of the cell.Rate this question:
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- 2.
A postaperative patient on intravenous fluids develops Iesi0ns in the mouth. Urinalysis indicates an excretion of 15pg riboflavin, which is abnormally low. Which of the following TCA enzymes is most likely to be affected?
- A.
Citrate synthase
- B.
Isocitrate dhydrogenase
- C.
Fumarase
- D.
Succinate dhydrogenase
- E.
Malate dehydrogenase
Correct Answer
D. Succinate dhydrogenaseExplanation
Succinate dehydrogenase is an enzyme involved in the citric acid cycle (TCA cycle) and electron transport chain. It is responsible for the conversion of succinate to fumarate. A deficiency in succinate dehydrogenase can lead to a decrease in energy production and accumulation of succinate, which can result in a variety of symptoms including mouth lesions and low levels of riboflavin excretion. Therefore, it is likely that succinate dehydrogenase is affected in this postoperative patient.Rate this question:
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- 3.
Citrate synthase, the first reaction in theTCA cycle, regulates the IeveIs of Citrate within the cell. WhIch of the foIIowing does not describe citrate's role in Metabolic regulation?
- A.
It is positively regulated by oxaloacetate
- B.
It combines the two carbons of acetyl CoA with oxaloacetate.
- C.
It is positively reguIated by succinyl-CoA
- D.
It is negatively regulated by ATP.
- E.
Its product, citrate, helps shuttle acetyl CoA during lipid metabolism
Correct Answer
C. It is positively reguIated by succinyl-CoAExplanation
Citrate synthase is not positively regulated by succinyl-CoA. Instead, succinyl-CoA acts as a negative regulator of citrate synthase.Rate this question:
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- 4.
The major metabolic consequence that would result from inhibition of Complex I in the electron transport chain by rotenone would be:
- A.
Increased production of FADH2
- B.
Increased oxidation of NADH
- C.
Increased reduction of O2 to H20
- D.
Decreased regeneration of NAD+
- E.
Increased pumping of protons by complex I,II and III.
Correct Answer
D. Decreased regeneration of NAD+Explanation
Inhibition of Complex I in the electron transport chain by rotenone would lead to decreased regeneration of NAD+. Complex I plays a crucial role in the regeneration of NAD+ from NADH during cellular respiration. NAD+ is required for the continuation of glycolysis and the citric acid cycle, which are important steps in energy production. Therefore, inhibition of Complex I would disrupt this process and result in decreased regeneration of NAD+.Rate this question:
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- 5.
Complex II differs from the other three complexes of the electron transport Chain in one major aspect. What is the aspect?
- A.
It is not located on the inner membrane of the mitochondria
- B.
It does not contain cofactors
- C.
It does not pump protons
- D.
It requires ATP for its reaction
Correct Answer
C. It does not pump protonsExplanation
Complex II differs from the other three complexes of the electron transport chain in that it does not pump protons. The other complexes, Complex I, Complex III, and Complex IV, all use the energy from electron transfer to pump protons across the inner membrane of the mitochondria, creating a proton gradient. This proton gradient is essential for ATP synthesis. However, Complex II, also known as succinate dehydrogenase, does not pump protons. Instead, it transfers electrons directly to Coenzyme Q, bypassing the proton pumping step.Rate this question:
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- 6.
Complete the following phrase by filling in the blanks to make it a true statement. "The action of the inhibitor rotenone on the Complex I enzyme system of electron transport results in accumulation of_(1)__ which slows down _(2)__. This results in __(3)___
- A.
NADH; ATP synthesis; glycogen accumulation
- B.
NAD+; glycolysis; a higher membrane potential across the inner mitochondrral membrane
- C.
NAD+; ATP svnthesrs: enhanced fatty acid biosynthesis
- D.
NADH; the TCA cycle; accumulation of lactate
- E.
NAD+; the TCA cycle; enhanced gluconeogenesis
Correct Answer
D. NADH; the TCA cycle; accumulation of lactateExplanation
The action of the inhibitor rotenone on the Complex I enzyme system of electron transport results in accumulation of NADH, which slows down the TCA cycle. This results in accumulation of lactate.Rate this question:
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- 7.
Dental plaque contains bacteria that produce lactic acid from glucose. Lactic acid is sufficiently acidic to dissolve calcium phosphates in tooth enamel, and this contributes to dental caries (cavities). Which of the following enzymes does the fluoride in toothpaste inhibit in the cariogenic bacterium Streptococcus mutans, thereby reducing lactic acid production on the enamel surface of teeth?
- A.
Hexokinase
- B.
Glucose 6-phosphate isomerase
- C.
Aldolase
- D.
Enolase
- E.
Pyruvate kinase
Correct Answer
D. EnolaseExplanation
Enolase is the correct answer because fluoride in toothpaste inhibits this enzyme in the cariogenic bacterium Streptococcus mutans. Enolase is responsible for the conversion of 2-phosphoglycerate to phosphoenolpyruvate in the glycolysis pathway. By inhibiting enolase, fluoride reduces the production of lactic acid from glucose in the bacteria, thereby helping to prevent the dissolution of calcium phosphates in tooth enamel and the formation of dental caries.Rate this question:
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- 8.
Streptococcus pneumoniae is the primary cause of community-acquired pneumonia. The bacterium in blood plasma has a five-fold reduced transcription of the phosphofructokinase-l gene. Assuming that glycolysis is similar in S.pneumoniae and H, sapiens, what is most likely to result from reduced transcription of the PFK-l gene in the bacteria?
- A.
Glucose utilization increases
- B.
Glucose production from lactate is reduced
- C.
The rate of lactate formation increases
- D.
The amount of glyceraldehyde 3-phosphate increases
- E.
The amount of fructose 6-phosphate increases
Correct Answer
E. The amount of fructose 6-phosphate increasesExplanation
Reduced transcription of the phosphofructokinase-l gene in Streptococcus pneumoniae would result in an increase in the amount of fructose 6-phosphate. Phosphofructokinase is an enzyme involved in the regulation of glycolysis, and fructose 6-phosphate is an intermediate in the glycolytic pathway. With reduced transcription of the PFK-l gene, the production of phosphofructokinase would be decreased, leading to an accumulation of fructose 6-phosphate. This would disrupt the normal flow of glycolysis and could potentially affect the overall metabolism of the bacteria.Rate this question:
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- 9.
A worker in a chemical factory falls into a vat with pentachlorophenol, a wood preservative that uncouples oxidative phosphorylation and that can be absorbed through the skin. Which of the following anomalies can you expect as a result (while the patient is still alive)?
- A.
Hypothermia (reduced body temperature), because mitochondrial energy generation is impaired
- B.
A slowdown of all catabolic pathways including glycolysis (while the patient is still alive)
- C.
All redox couples in the respiratory chain will be trapped in the reduced state
- D.
Glycogen phosphorylase is activated
- E.
ATP can no longer be synthesized from carbohydrates, but ATP synthesis from fatty acids is intact
Correct Answer
D. Glycogen phosphorylase is activatedExplanation
When a worker falls into a vat with pentachlorophenol, a wood preservative that uncouples oxidative phosphorylation, it impairs mitochondrial energy generation. This leads to a reduction in body temperature, causing hypothermia. Additionally, the impairment in energy generation slows down all catabolic pathways, including glycolysis. As a result, all redox couples in the respiratory chain will be trapped in the reduced state. However, despite the impairment in ATP synthesis from carbohydrates, ATP synthesis from fatty acids remains intact. In this scenario, the activation of glycogen phosphorylase is expected as a result.Rate this question:
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- 10.
at the funeraI of the worker in question 9, some of the mourners get severely ill after eating cassava puree, which still contained toxic quantities of cyanide due to improper processinq of the cassava root. Which abnormalities do you expect in these patients?
- A.
Cyanosis, due to reduced oxygen saturation of hemoglobin
- B.
Reduced activity of phosphofructokinase-1
- C.
Lactic acidosis
- D.
The p/o ratio for the mitochondrial oxidation of NADH is reduced
- E.
Hypoventilation
Correct Answer
C. Lactic acidosisExplanation
The patients who consumed the cassava puree containing toxic quantities of cyanide are likely to experience lactic acidosis. Lactic acidosis occurs when there is an accumulation of lactic acid in the bloodstream due to the inability of the body to properly metabolize it. Cyanide inhibits the enzyme cytochrome c oxidase, which is involved in the mitochondrial oxidation of NADH. This leads to an impaired electron transport chain and a subsequent shift towards anaerobic metabolism, resulting in the production of lactic acid. Therefore, lactic acidosis is a common manifestation of cyanide poisoning.Rate this question:
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- 11.
A research group reported that transgenic mice overexpressing the human catalase gene in mitochondria have a 5-month increase in median lifespan . What is the substrate and the coenzyme for the human catalase enzyme, respectively?
- A.
Superoxide anion, and ATP
- B.
Hydrogen peroxide, and heme
- C.
Organic peroxy radicals, and thiamine pyrophosphate
- D.
Hydroxyl radicals, and FMN
- E.
Coenzyme Q, and NADH
Correct Answer
B. Hydrogen peroxide, and hemeExplanation
The correct answer is hydrogen peroxide and heme. Catalase is an enzyme that helps break down hydrogen peroxide into water and oxygen. Hydrogen peroxide is the substrate, which is the molecule that the enzyme acts upon. Heme is the coenzyme, which is a non-protein molecule that helps the enzyme carry out its function.Rate this question:
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- 12.
The liver converts a molecule of citric acid, obtained from lemon juice, into succinyl-CoA. Succinyl-CoA is subsequently used for heme biosynthesis. Approximately, how many ATP (plus GTP) molecules can be derived from the conversion of one molecuIe of citrate to succinyI-CoA"'
- A.
3
- B.
6
- C.
7
- D.
9
- E.
12
Correct Answer
B. 6Explanation
The conversion of citrate to succinyl-CoA occurs in the citric acid cycle, also known as the Krebs cycle. During this cycle, one molecule of citrate is converted into one molecule of succinyl-CoA. In this process, three molecules of NADH and one molecule of FADH2 are produced. Each NADH molecule can generate 2.5 ATP molecules, and each FADH2 molecule can generate 1.5 ATP molecules. Therefore, the total number of ATP molecules that can be derived from the conversion of one molecule of citrate to succinyl-CoA is 3 (NADH) x 2.5 + 1 (FADH2) x 1.5 = 7.5. Since GTP can be converted to ATP, we can consider it as an additional ATP molecule. Therefore, the total number of ATP (plus GTP) molecules derived is 7.5 + 1 = 8. However, since the question asks for the approximate number of ATP (plus GTP) molecules, the closest option is 6.Rate this question:
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- 13.
Another molecule of citric acid from the same glass of lemon juice is converted to oxaloacetate, which is subsequentfy processed into glucose. How many molecules of ATP and/or GTP do the reactions from citrate to oxaloacetate produce, either directly or indirectly through the respiratory chain?
- A.
3
- B.
6
- C.
7
- D.
9
- E.
12
Correct Answer
E. 12 -
- 14.
Thiamine deficiency will not only lead to the accumulation of pyruvate and lactate, but also the accumulation of:
- A.
Succinyl-CoA
- B.
Oxaloacetate
- C.
Malate
- D.
Succinate
- E.
A-ketoglutarate
Correct Answer
E. A-ketoglutarateExplanation
Thiamine deficiency can lead to a decrease in the activity of the enzyme alpha-ketoglutarate dehydrogenase, which is involved in the citric acid cycle. This enzyme is responsible for converting alpha-ketoglutarate to succinyl-CoA. Therefore, when thiamine is deficient, there will be an accumulation of alpha-ketoglutarate.Rate this question:
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- 15.
A young girl is brought into the emergency room on the verge of death due to exposure to a mitochondriaI poison, Her mitochondriaI oxygen consumption is very low and she cannot produce ATP through oxidatlve phosphorylation consumption. Finally, the mitochondria have an excess of NADH and very little reduced coenzyme Q (QH2) . To which of the following poisons was the patient exposed?
- A.
Oligomycin
- B.
Cyanide
- C.
Azide
- D.
Pentachlorophenol
- E.
Amytal
Correct Answer
E. AmytalExplanation
The patient's symptoms suggest exposure to Amytal, a mitochondrial poison that inhibits the electron transport chain. This leads to a decrease in mitochondrial oxygen consumption and the inability to produce ATP through oxidative phosphorylation. The excess of NADH and lack of reduced coenzyme Q (QH2) further support this conclusion.Rate this question:
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- 16.
The rate at which pyruvate from gIycoIysis is used by the TCA cycle to produce energy is regulated by pyruvate dehydrogenase. During muscle contraction, this enzyme is
- A.
Inhibited by increases in the Ca-2 concentration.
- B.
Activated by increases in acetyl CoA
- C.
Activated by increases in NADH
- D.
Activated by increases In ADP
- E.
Inhibited by increases In AMP
Correct Answer
D. Activated by increases In ADPExplanation
During muscle contraction, there is an increased demand for energy. ADP is a molecule that indicates low energy levels in the cell. When ADP levels increase, it signals the need for more energy production. Pyruvate dehydrogenase is activated by increases in ADP, which means that it becomes more active and converts pyruvate from glycolysis into acetyl CoA, which enters the TCA cycle to produce energy. Therefore, the increase in ADP activates pyruvate dehydrogenase and allows for a higher rate of energy production during muscle contraction.Rate this question:
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- 17.
A postoperative patient on Intravenous fluids develops lesions in the Mouth ( angular stomatitis). UrinalysIs indicates an excretion of 15ug Riboflavin/mg-creatinine, which is abnormally low. Which of the following TCA enzymes is most likely to be effected?
- A.
Citrate synthase
- B.
Isocitrate dehydrogenase
- C.
Fumarase
- D.
Malate dehydrogenase
- E.
Succinate dehydrogenase
Correct Answer
E. Succinate dehydrogenaseExplanation
The development of lesions in the mouth (angular stomatitis) and the abnormally low excretion of riboflavin in the urine suggest a deficiency in riboflavin (vitamin B2). Riboflavin is an important cofactor for many enzymes, including succinate dehydrogenase, which is part of the tricarboxylic acid (TCA) cycle. Therefore, the most likely TCA enzyme to be affected in this case is succinate dehydrogenase.Rate this question:
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Mar 21, 2023Quiz Edited by
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Nov 11, 2011Quiz Created by
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