Vitamins and Coenzymes Practice Questions

Q: Which of the following supplements is used in the treatment of multiple carboxylase deficiency?

Biotin. **Explanation:** **Multiple Carboxylase Deficiency (MCD)** is a metabolic disorder caused by defects in either **holocarboxylase synthetase** (early-onset) or **biotinidase** (late-onset). Both enzymes are essential for the normal cycling and utilization of **Biotin (Vitamin B7)**. **Why Biotin is the correct answer:** Biotin serves as a vital coenzyme for four major carboxylases in the body: 1. **Pyruvate carboxylase** (Gluconeogenesis) 2. **Acetyl-CoA carboxylase** (Fatty acid synthesis) 3. **Propionyl-CoA carboxylase** (Amino acid catabolism) 4. **3-Methylcrotonyl-CoA carboxylase** (Leucine catabolism) In MCD, these enzymes cannot function because biotin is not properly attached to them or recycled. High-dose pharmacological supplementation of **Biotin** bypasses these defects, restoring enzyme activity and resolving clinical symptoms like dermatitis, alopecia, and metabolic acidosis. **Why other options are incorrect:** * **Pyridoxine (B6):** Coenzyme for transamination and decarboxylation (e.g., ALT, AST, GAD). Deficiency leads to sideroblastic anemia and seizures. * **Thiamine (B1):** Coenzyme for oxidative decarboxylation (e.g., Pyruvate dehydrogenase). Deficiency causes Beriberi and Wernicke-Korsakoff syndrome. * **Folic acid (B9):** Involved in one-carbon metabolism and DNA synthesis. Deficiency causes megaloblastic anemia. **High-Yield Clinical Pearls for NEET-PG:** * **The "CO2 Fixer":** Biotin is always the coenzyme for carboxylases (except Vitamin K-dependent carboxylation). * **Egg White Injury:** Raw egg whites contain **Avidin**, which binds biotin tightly and prevents its absorption, potentially leading to deficiency. * **Clinical Triad:** Suspect MCD in infants presenting with **alopecia, skin rash, and lactic acidosis.**

Q: Vitamin E is responsible for all the following functions EXCEPT:

It cures the oxidation of low-density lipoproteins.. **Explanation:** Vitamin E (Tocopherol) is a potent lipid-soluble antioxidant that functions primarily as a free radical scavenger. **Why Option D is the correct answer:** The statement "It cures the oxidation of low-density lipoproteins" is incorrect because Vitamin E **prevents** or inhibits the oxidation of LDL; it does not "cure" or reverse oxidation once it has occurred. Oxidized LDL is a major pro-atherogenic factor; by preventing its formation, Vitamin E helps reduce the risk of atherosclerosis. **Analysis of other options:** * **Option A:** Vitamin E is the primary defense against **lipid peroxidation**. It protects polyunsaturated fatty acids (PUFAs) in biological membranes from being damaged by reactive oxygen species (ROS). * **Option B:** By protecting the erythrocyte membrane from oxidative stress, Vitamin E **prevents hemolysis**. Deficiency of Vitamin E is a known cause of hemolytic anemia, especially in premature infants. * **Option C:** In animal models (specifically rats), Vitamin E deficiency leads to germinal epithelium degeneration and sterility. Thus, it is historically labeled the **"anti-sterility vitamin,"** though this effect is less clearly defined in humans. **High-Yield Clinical Pearls for NEET-PG:** * **Most active form:** $\alpha$-tocopherol is the most biologically active form. * **Synergy:** Vitamin E works in tandem with **Vitamin C** (which regenerates reduced tocopherol) and **Selenium** (as part of glutathione peroxidase). * **Deficiency:** Presents with posterior column signs (loss of proprioception/vibration), ataxia, and hemolytic anemia, mimicking Friedreich’s ataxia. * **Toxicity:** High doses can interfere with Vitamin K action, leading to an increased risk of hemorrhages.

Q: Vitamin K deficiency is indicated by which of the following laboratory findings?

Increased prothrombin time. **Explanation:** **1. Why the correct answer is right:** Vitamin K is an essential fat-soluble vitamin that acts as a cofactor for the enzyme **$\gamma$-glutamyl carboxylase**. This enzyme is responsible for the post-translational modification (carboxylation of glutamate residues) of specific clotting factors: **Factors II (Prothrombin), VII, IX, and X**, as well as Proteins C and S. In Vitamin K deficiency, these factors are synthesized but remain inactive (known as PIVKAs—Proteins Induced by Vitamin K Absence). Since Factor VII has the shortest half-life and is part of the **extrinsic pathway**, its deficiency rapidly leads to an **increased Prothrombin Time (PT)**. While the Activated Partial Thromboplastin Time (aPTT) may also increase in severe cases, PT is the most sensitive clinical marker for Vitamin K status. **2. Why the incorrect options are wrong:** * **Option A (Low platelet count):** Vitamin K is involved in the coagulation cascade (secondary hemostasis), not platelet production or survival (primary hemostasis). Thrombocytopenia is typically seen in bone marrow disorders or hypersplenism. * **Option C (Decreased prothrombin time):** A decreased PT indicates a hypercoagulable state, whereas Vitamin K deficiency leads to a bleeding diathesis due to the inability to form clots. **3. NEET-PG High-Yield Pearls:** * **Warfarin Mechanism:** Warfarin acts as a Vitamin K antagonist by inhibiting **Vitamin K epoxide reductase**, preventing the recycling of Vitamin K. * **Newborns:** They are prone to Vitamin K deficiency (Hemorrhagic Disease of the Newborn) due to sterile guts and poor placental transfer; hence, a prophylactic IM dose of Vitamin K is given at birth. * **Absorption:** Being fat-soluble, its deficiency is often secondary to fat malabsorption (e.g., obstructive jaundice, celiac disease).

Q: White polished rice causes deficiency of which vitamin?

Thiamine. **Explanation:** **Correct Answer: A. Thiamine (Vitamin B1)** Thiamine is primarily located in the outer layer (pericarp) and the germ of cereal grains. The process of **milling and polishing rice** removes these outer layers (bran), stripping the grain of its thiamine content. Consequently, populations that rely heavily on white polished rice as a staple food are at high risk for Thiamine deficiency, classically manifesting as **Beriberi**. **Analysis of Incorrect Options:** * **B. Tryptophan:** This is an essential amino acid, not a vitamin. Its deficiency is associated with maize (corn)-based diets, as maize is deficient in tryptophan, leading to Pellagra (since tryptophan is a precursor for Niacin). * **C. Riboflavin (Vitamin B2):** While milling reduces riboflavin levels, the clinical hallmark of polished rice consumption is specifically thiamine deficiency. Riboflavin deficiency (Ariboflavinosis) typically presents with cheilosis and glossitis. * **D. Protein:** While polished rice is low in protein, its consumption specifically triggers micronutrient deficiency (B1) rather than primary Protein-Energy Malnutrition (PEM), unless the overall caloric intake is also insufficient. **High-Yield Clinical Pearls for NEET-PG:** * **Dry Beriberi:** Characterized by peripheral neuropathy and muscle wasting. * **Wet Beriberi:** Characterized by high-output heart failure and edema. * **Wernicke-Korsakoff Syndrome:** Thiamine deficiency often seen in chronic alcoholics; presents with the triad of ataxia, ophthalmoplegia, and confusion. * **Enzyme Link:** Thiamine pyrophosphate (TPP) is a vital coenzyme for **Pyruvate Dehydrogenase** and **Alpha-ketoglutarate dehydrogenase**. Deficiency leads to impaired aerobic metabolism and lactic acidosis.

Q: Hypervitaminosis D may cause all of the following EXCEPT:

Remineralization of bone. **Explanation:** Vitamin D toxicity (Hypervitaminosis D) is characterized by excessive levels of 1,25-dihydroxyvitamin D, which leads to **hypercalcemia** and **hypercalciuria**. **Why "Remineralization of bone" is the correct answer:** Contrary to its physiological role in bone formation at normal levels, excessive Vitamin D stimulates high levels of **osteoclast activity**. This leads to increased bone resorption (demineralization), mobilizing calcium from the bones into the bloodstream. Therefore, hypervitaminosis D causes **demineralization**, not remineralization. **Analysis of Incorrect Options:** * **Deposition of calcium in arteries:** Hypercalcemia leads to **metastatic calcification**. Calcium deposits in soft tissues, including the media of arteries, heart, and lungs. * **Renal calculi:** Increased intestinal absorption and bone resorption lead to hypercalciuria (excess calcium in urine). This promotes the formation of calcium oxalate or calcium phosphate stones in the kidneys. * **Loss of appetite:** Anorexia (loss of appetite), nausea, and vomiting are early clinical symptoms of hypercalcemia affecting the gastrointestinal tract. **High-Yield NEET-PG Pearls:** * **Mechanism:** Vitamin D toxicity is usually due to over-supplementation, not sunlight, as the body degrades excess Vitamin D in the skin. * **Clinical Triad:** Hypercalcemia, Hypercalciuria, and Polyuria. * **Williams Syndrome:** A condition characterized by hypersensitivity to Vitamin D, leading to idiopathic infantile hypercalcemia. * **Treatment:** Immediate cessation of Vitamin D/Calcium intake, aggressive hydration, and administration of glucocorticoids (which decrease intestinal calcium absorption).

Q: The deficiency of thiamine can be identified by measuring the red cell:

Transketolase. **Explanation:** Thiamine (Vitamin B1) serves as a vital cofactor in the form of **Thiamine Pyrophosphate (TPP)** for several key enzymes in carbohydrate metabolism. **Why Transketolase is the correct answer:** The erythrocyte (red cell) transketolase activation assay is the **gold standard** for diagnosing thiamine deficiency. Transketolase is an enzyme in the Pentose Phosphate Pathway (HMP Shunt) that requires TPP. In this diagnostic test, transketolase activity is measured before and after the addition of exogenous TPP. An increase in activity (>15-25%) indicates a biochemical thiamine deficiency. Red cells are used because they are easily accessible and reflect the body's overall thiamine status. **Why other options are incorrect:** * **B. Transaldolase:** Although it functions in the HMP shunt alongside transketolase, it is **not** TPP-dependent and thus cannot be used to measure thiamine levels. * **C & D. Alpha-ketoglutarate dehydrogenase and Pyruvate dehydrogenase:** Both are indeed TPP-dependent enzymes (part of the TCA cycle and link reaction). However, they are mitochondrial enzymes. Since mature red blood cells lack mitochondria, these enzymes cannot be measured in a red cell assay. **High-Yield Clinical Pearls for NEET-PG:** * **TPP-dependent enzymes (Mnemonic: APT):** **A**lpha-ketoglutarate dehydrogenase, **P**yruvate dehydrogenase, and **T**ransketolase (also Branched-chain ketoacid dehydrogenase). * **Clinical Deficiency:** Presents as **Beriberi** (Dry: polyneuritis; Wet: high-output heart failure) or **Wernicke-Korsakoff Syndrome** (Ataxia, Ophthalmoplegia, Confusion, and Confabulation). * **Rule of Thumb:** Always administer thiamine *before* glucose in malnourished/alcoholic patients to prevent precipitating Wernicke encephalopathy, as glucose oxidation consumes the remaining TPP.

Question 1

Which of the following supplements is used in the treatment of multiple carboxylase deficiency?

Accepted Answer

Biotin

Answer

Pyridoxin

Answer

Thiamine

Answer

Folic acid

Question 2

Which of the following is least affected in Vitamin C deficiency?

Accepted Answer

Epithelial lining of the mucosa

Answer

Gingival fibres

Answer

Periodontal ligament

Answer

Blood vessels of the gingiva

Question 3

Vitamin E is responsible for all the following functions EXCEPT:

Accepted Answer

It cures the oxidation of low-density lipoproteins.

Answer

It prevents lipid peroxidation in biological membranes.

Answer

It prevents RBCs from hemolysis.

Answer

It is considered to be the anti-sterility vitamin.

Question 4

The pro-oxidant action of Vitamin C is potentiated by:

Accepted Answer

Copper

Answer

Selenium

Answer

Calcium

Answer

Iron

Question 5

Vitamin K deficiency is indicated by which of the following laboratory findings?

Accepted Answer

Increased prothrombin time

Answer

Low platelet count

Answer

Decreased prothrombin time

Answer

None of the above

Question 6

Which of the following is associated with elevated alkaline phosphatase, low calcium, and low phosphate?

Accepted Answer

Vitamin D deficiency

Answer

Paget's disease

Answer

Osteoporosis

Answer

Primary hyperparathyroidism

Question 7

White polished rice causes deficiency of which vitamin?

Accepted Answer

Thiamine

Answer

Tryptophan

Answer

Riboflavin

Answer

Protein

Question 8

Thiamine deficiency in a chronic alcoholic can reduce energy production as a result of which of the following reasons?

Accepted Answer

It is a co-enzyme for pyruvate dehydrogenase and a-ketoglutarate dehydrogenase in the TCA pathway

Answer

It is required for the process of transamination

Answer

It is a co-factor for oxidative reduction

Answer

It is a co-enzyme for transketolase in the pentose phosphate pathway

Question 9

Hypervitaminosis D may cause all of the following EXCEPT:

Accepted Answer

Remineralization of bone

Answer

Deposition of calcium in arteries

Answer

Renal calculi

Answer

Loss of appetite

Question 10

The deficiency of thiamine can be identified by measuring the red cell:

Accepted Answer

Transketolase

Answer

Transaldolase

Answer

Alpha ketoglutarate dehydrogenase

Answer

Pyruvate dehydrogenase

Vitamins and Coenzymes — MCQs

Vitamins and Coenzymes — MCQs

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