Mcq_mini3_(4)[1] Tca Cycle And Oxidative Phosphorylation

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.

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+.

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.

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.

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.

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.

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.

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.

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.

Citrate synthase is not positively regulated by succinyl-CoA. Instead, succinyl-CoA acts as a negative regulator of citrate synthase.

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.

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.

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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.

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.

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.

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.