Nucleotide metabolism-Multiple-choice questions with explanations

Practice questions, USMLE styled question bank /

Question 1: A 3-month-old male infant presents with delayed motor development and orange, sand-like crystals in his diaper. His parents report he constantly chews on his fingers and lips, causing bleeding. Based on these symptoms, what is the most likely diagnosis? A. Adenosine deaminase deficiency B. Gouty arthritis C. Lesch-Nyhan Syndrome D. Orotic aciduria E. […]

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Nucleotide metabolism- Short-answer questions

Short-answer Questions /

Question 1: What is the initial step in the synthesis of both purine and pyrimidine nucleotides? Answer: The initial step in the synthesis of both purine and pyrimidine nucleotides is the synthesis of PRPP (5-phosphoribosyl-1-pyrophosphate) from D-ribose-5’-P. Question 2: What is the significance of Mycophenolic acid in purine nucleotide biosynthesis? Answer: Mycophenolic acid is an

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Fructose and Galactose metabolism- Multiple-choice questions with explanations

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1. An exclusively breast-fed infant presents with vomiting, weight loss, jaundice, hepatomegaly, and bilateral cataracts. Which condition is most likely responsible for these symptoms? A. Breast milk jaundice B. Classical Galactosemia C. Hereditary fructose intolerance D. Type 1 Diabetes mellitus E. Von Gierke’s disease Correct Answer: B. Classical Galactosemia Explanation: Classical galactosemia is a rare

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Fructose and Galactose metabolism- Short-answer questions

Short-answer Questions /

Question 1: What are the two ways fructose exists in food? Answer: Fructose exists in food as a monosaccharide (free fructose) or as a unit of a disaccharide (sucrose). Question 2: What is the name of the transporter protein responsible for fructose absorption in the intestine? Answer: Fructose absorption in the intestine occurs via facilitated

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Summary of Amino acid disorders with easy recall mnemonics

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  Disorder Defective Enzyme/Transporter Clinical Picture Mnemonic Phenylketonuria (PKU) Phenylalanine hydroxylase Musty body odor, intellectual disability, seizures, pale skin, eczema Pale kids with Krappy Urine Alkaptonuria Homogentisic acid oxidase Black urine, ochronosis (bluish-black pigmentation in connective tissues), arthritis Black CAP: Cartilage, Arthritis, Pigmentation Maple Syrup Urine Disease (MSUD) Branched-chain α-ketoacid dehydrogenase Sweet-smelling urine, poor feeding,

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Ammonia Disposal – Short-answer questions

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Question 1: What is the primary function of the urea cycle in humans? Answer: The urea cycle converts ammonia, a highly toxic byproduct of amino acid metabolism, into urea, a less toxic compound that can be safely excreted in urine. This process is vital for maintaining nitrogen balance in the body. Question 2: Which cellular

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Amino Acid Metabolism-Multiple-Choice Questions- Set 1

Practice questions, USMLE styled question bank /

Q.1 – Which of the following is a common compound shared by the TCA (Tricarboxylic Acid) cycle and the Urea cycle? A. α-Ketoglutarate B. Succinyl-CoA C. Oxaloacetate D. Fumarate E. Citrate Correct Answer: D. Fumarate Explanation: Fumarate is a key intermediate shared between the TCA and Urea cycles. In the Urea cycle, fumarate is produced

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Fatty acid oxidation and TG breakdown- Short answer questions

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Question 1: Why are triglycerides a more efficient energy storage form compared to glycogen? Answer: Triglycerides are highly reduced and stored in a nearly anhydrous form, yielding about 9 kcal/g upon complete oxidation. In contrast, the polar nature of glycogen leads to greater hydration, reducing its energy storage capacity to about 1/6th that of fat.

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Gluconeogenesis- Short answer questions

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Question 1: Explain why gluconeogenesis is not simply the reverse of glycolysis. Answer: Gluconeogenesis is not simply the reverse of glycolysis because there are three irreversible reactions in glycolysis that must be bypassed in gluconeogenesis. These irreversible reactions are catalyzed by hexokinase, phosphofructokinase, and pyruvate kinase. Gluconeogenesis uses different enzymes to bypass these steps, making

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Amino acids associated with the TCA cycle and their entry points (with easy mnemonics)

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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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