Gluconeogenesis- Case-based Multiple-Choice Questions- Set 1

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1. A 4-month-old boy is being evaluated for seizures, psychomotor retardation, and hypotonia. Work-up reveals elevated serum levels of lactate, alanine, pyruvate, and ketoacids. Based on the clinical presentation, pyruvate carboxylase activity is measured using fibroblasts from a skin biopsy and is found to be markedly decreased. This enzyme is normally used to directly synthesize […]

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Amphibolic Role of the TCA Cycle with Mnemonics

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The TCA cycle (Krebs cycle) serves as a central hub for both catabolic (energy-producing) and anabolic (biosynthetic) processes, making it a dual-purpose amphibolic pathway. Below is a table that summarizes the catabolic and anabolic roles of the TCA cycle, along with mnemonics to make these concepts easier to remember. Catabolic Role of the TCA Cycle:

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Electron Transport Chain and Oxidative Phosphorylation- Multiple Choice Questions With Explanations-Set-2

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11. A 48-year-old patient is brought to the emergency room after exposure to toxic fumes suspected to contain cyanide. He presents with shortness of breath, confusion, and metabolic acidosis. The medical team suspects cyanide toxicity, which disrupts the electron transport chain (ETC). Which of the following statements concerning the components of the electron transport chain

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Electron Transport Chain and Oxidative Phosphorylation- Multiple Choice Questions With Explanations-Set-1

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1. A 60-year-old man is admitted to the hospital with confusion, fatigue, and muscle weakness. His symptoms suggest mitochondrial dysfunction, potentially caused by exposure to a toxin that inhibits the electron transport chain. Laboratory tests reveal a disruption in ATP production, and the medical team suspects inhibition at Complex I. Which of the following is

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A Summary Of Regulation of Glycolysis, PDH Complex, and TCA Cycle (with mnemonics)

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Hexokinase vs Glucokinase Regulation Feature Hexokinase Glucokinase Mnemonic Location Most tissues (muscle, brain) Liver and pancreatic β-cells “H in Human Tissues, G in Glucose Factories” Affinity for Glucose (Km) Low Km (high affinity) High Km (active only at high glucose) “Hexokinase is Hungry, Glucokinase is Greedy” Allosteric Inhibition Inhibited by Glucose-6-Phosphate No inhibition by Glucose-6-Phosphate

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ETC Inhibitors, Uncouplers, and Transporter Inhibitors of Oxidative Phosphorylation

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Site of Action Inhibitors / Uncouplers Mechanism Mnemonic for Easy Recall Complex I (NADH Dehydrogenase) Rotenone, Piericidin A, Amytal Blocks electron transfer from NADH to CoQ “Rotten Pies Available” (Rotenone, Piericidin A, Amytal block Complex I) Complex II (Succinate Dehydrogenase) Malonate, Carboxin, TTFA Competes with succinate, preventing electron transfer to CoQ “Malonate Causes Trouble Fast”

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Types of Enzyme Inhibition with Mnemonics

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Type of Inhibition Effect on Vmax and Km Reversible / Irreversible Examples Mnemonic Competitive (Inhibitor competes with substrate for the active site) Vmax: Unchanged Km: Increased Reversible 1) Statins – inhibit HMG-CoA Reductase (cholesterol-lowering) 2) PABA – inhibits Pteroyl Synthase (antibiotic) 3) Captopril – inhibits ACE (antihypertensive) 4) Oxamate – inhibits Lactate Dehydrogenase (poison) 5)

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Amino acids associated with the TCA cycle and helpful mnemonics to aid memorization

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Here’s a table showing the amino acids associated with each intermediate and helpful mnemonics to aid memorization: Intermediate Amino Acids Associated Mnemonic for Amino Acid Entry Points Pyruvate Glycine, Alanine, Serine, Cysteine, Threonine, Tryptophan, Hydroxyproline G – Glycine A – Alanine S – Serine C – Cysteine T – Threonine T – Tryptophan H – Hydroxyproline

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PDH complex and the TCA cycle- NBME style questions set-2

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1. The cytosolic isoform of which of the following TCA cycle enzymes requires NADP⁺ as a coenzyme, which can be utilized in the reduced state for reductive biosynthesis? A. Aconitase B. Citrate Synthase C. Isocitrate Dehydrogenase D. Malate Dehydrogenase E. Succinate Dehydrogenase The correct answer is C: Isocitrate Dehydrogenase: The cytosolic isoform of isocitrate dehydrogenase

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PDH complex and the TCA cycle- NBME style questions set-1

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1. A 24-year-old woman presents with diarrhea, dysphagia, jaundice, and white transverse lines on her fingernails (Mee’s lines). She is diagnosed with arsenic poisoning. Arsenic poisoning inhibits which of the following enzymes? A. Citrate synthase B. Isocitrate dehydrogenase C. Malate dehydrogenase D. Succinate dehydrogenase E. α-Keto glutarate dehydrogenase complex Correct answer: E. α-Keto glutarate dehydrogenase

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