Vitamins and Coenzymes Practice Questions

Q: Which vitamin deficiency can cause rickets?

Vitamin D. **Explanation:** **Correct Answer: C. Vitamin D** Vitamin D (Calciferol) is essential for maintaining calcium and phosphate homeostasis. It promotes the intestinal absorption of calcium and phosphorus, which are critical for the mineralization of the bone matrix (osteoid). A deficiency in Vitamin D leads to inadequate mineralization. In children, where epiphyseal plates are still open, this results in **Rickets**, characterized by soft bones, skeletal deformities (like bow legs), and rachitic rosary. In adults, the same deficiency causes **Osteomalacia**. **Incorrect Options:** * **Vitamin C:** Deficiency leads to **Scurvy**. It is required for the hydroxylation of proline and lysine residues during collagen synthesis. Deficiency causes capillary fragility and gum bleeding, not primary mineralization defects. * **Niacin (B3):** Deficiency causes **Pellagra**, characterized by the "3 Ds": Dermatitis, Diarrhea, and Dementia. It is a precursor for NAD and NADP. * **Biotin (B7):** Serves as a coenzyme for carboxylation reactions (e.g., Pyruvate carboxylase). Deficiency is rare but typically presents with dermatitis, alopecia, and neurological symptoms, not bone pathology. **High-Yield Clinical Pearls for NEET-PG:** * **Active Form:** Calcitriol [1,25-(OH)₂D₃] is the most active form, synthesized in the kidney via the enzyme **1-alpha-hydroxylase**. * **Radiological Sign:** Look for "cupping and splaying" of metaphyses in Rickets. * **Biochemical Profile:** In Vitamin D deficiency, expect **Low Serum Calcium, Low Serum Phosphate, and Elevated Alkaline Phosphatase (ALP)**. Secondary Hyperparathyroidism is often present.

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.

Q: Which of the following is the synthetic vitamer of vitamin K?

Menadione. **Explanation:** Vitamin K exists in several forms, categorized based on their source and chemical structure. The correct answer is **Menadione (Vitamin K3)** because it is the only **synthetic, water-soluble** form of Vitamin K. Unlike natural forms, it lacks the long isoprenoid side chain, making it a provitamin that must be alkylated in the liver to become biologically active (menaquinone-4). **Analysis of Options:** * **Phylloquinone (Vitamin K1):** This is the **natural** form of Vitamin K synthesized by **plants**. It is the primary dietary source (found in green leafy vegetables) and is fat-soluble. * **Menaquinone (Vitamin K2):** This is the **natural** form synthesized by **intestinal bacterial flora**. It is also fat-soluble and plays a significant role in bone metabolism. * **Menadione (Vitamin K3):** As a synthetic compound, it was previously used for supplementation but is now restricted in clinical practice for neonates due to its potential to cause oxidative stress. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Vitamin K acts as a coenzyme for **$\gamma$-glutamyl carboxylase**, which converts glutamic acid residues to $\gamma$-carboxyglutamate (Gla) on clotting factors **II, VII, IX, and X**, as well as Proteins C and S. * **Warfarin Connection:** Warfarin inhibits **Vitamin K Epoxide Reductase (VKOR)**, preventing the regeneration of active Vitamin K (hydroquinone). * **Toxicity Warning:** Menadione (K3) can cause **hemolytic anemia, hyperbilirubinemia, and kernicterus** in infants because it reacts with sulfhydryl groups like glutathione, leading to oxidative damage to RBC membranes. * **Newborn Prophylaxis:** Since Vitamin K does not cross the placenta well and breast milk is a poor source, newborns receive an injection of **Phylloquinone (K1)** to prevent Hemorrhagic Disease of the Newborn.

Q: Deficiency of which vitamin causes spinocerebellar ataxia?

Vitamin E. **Explanation:** **Vitamin E (Tocopherol)** is a potent lipid-soluble antioxidant that protects cell membranes from oxidative damage. The nervous system is particularly vulnerable to oxidative stress. Deficiency leads to a clinical syndrome characterized by **spinocerebellar ataxia**, loss of vibratory and position sense (posterior column involvement), and absent deep tendon reflexes. This occurs because Vitamin E is essential for maintaining the integrity of the axons in the spinal cord (specifically the spinocerebellar tracts and dorsal columns). **Analysis of Options:** * **Vitamin B12 (Cobalamin):** Deficiency causes **Subacute Combined Degeneration (SCD)** of the spinal cord. While it involves the posterior columns and lateral corticospinal tracts, the classic presentation is megaloblastic anemia and "pins and needles" sensations, rather than pure spinocerebellar ataxia. * **Vitamin C (Ascorbic Acid):** Deficiency leads to **Scurvy**, characterized by defective collagen synthesis, capillary fragility (petechiae, bruising), and bleeding gums. It does not cause primary neurological degeneration. * **Vitamin A (Retinol):** Deficiency primarily affects vision (night blindness, xerophthalmia) and epithelial integrity (Bitot’s spots, follicular hyperkeratosis). **High-Yield Clinical Pearls for NEET-PG:** * **Mimicry:** Vitamin E deficiency presents almost identically to **Friedreich’s Ataxia**. * **Hemolysis:** In addition to neurological symptoms, Vitamin E deficiency can cause **hemolytic anemia** due to increased oxidative fragility of RBC membranes. * **Risk Factors:** It is most commonly seen in patients with fat malabsorption syndromes (e.g., Cystic Fibrosis, Abetalipoproteinemia, or Chronic Cholestasis). * **Key Tracts involved:** Spinocerebellar tract (ataxia) and Dorsal columns (loss of proprioception).

Q: The given condition is caused due to deficiency of which of the following?

Zinc. ***Zinc*** - **Acrodermatitis enteropathica** is the pathognomonic skin manifestation of **zinc deficiency**, presenting with perioral, perianal, and acral dermatitis. - Zinc is essential for **wound healing**, **immune function**, and maintaining skin integrity, particularly in rapidly dividing cells. *Niacin* - **Niacin deficiency** causes **pellagra** with the "4 Ds": dermatitis, diarrhea, dementia, and death. - The dermatitis in pellagra typically presents as **photosensitive** skin lesions in sun-exposed areas, not the perioral/perianal pattern seen here. *Iron* - **Iron deficiency** primarily causes **microcytic anemia** with symptoms like fatigue, pallor, and koilonychia (spoon nails). - Iron deficiency does not typically cause the characteristic **acrodermatitis enteropathica** skin pattern observed in this condition. *Selenium* - **Selenium deficiency** can cause **Keshan disease** (cardiomyopathy) and **Kashin-Beck disease** (osteoarthropathy). - Selenium deficiency does not produce the distinctive **perioral and perianal dermatitis** that characterizes zinc deficiency.

Q: A constellation of neuropathy, muscle weakness and wasting, cardiomegaly, edema, and ophthalmoplegia strongly suggests which of the following deficiencies?

Thiamine deficiency. **Explanation:** The clinical presentation described is a classic manifestation of **Thiamine (Vitamin B1) deficiency**, which presents in two major forms: **Dry Beriberi** and **Wet Beriberi**, often accompanied by **Wernicke-Korsakoff Syndrome**. 1. **Why Thiamine is correct:** Thiamine pyrophosphate (TPP) is a vital cofactor for enzymes like pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase. Deficiency leads to ATP depletion, affecting high-energy tissues: * **Dry Beriberi:** Characterized by peripheral neuropathy, muscle wasting, and weakness. * **Wet Beriberi:** Involves the cardiovascular system, leading to high-output heart failure, **cardiomegaly**, and **edema**. * **Wernicke Encephalopathy:** Presents with the triad of **ophthalmoplegia** (eye muscle paralysis), ataxia, and confusion. 2. **Why other options are incorrect:** * **Cobalamin (B12):** Deficiency causes Subacute Combined Degeneration of the spinal cord (SCD) and megaloblastic anemia, but not cardiomegaly or acute ophthalmoplegia. * **Niacin (B3):** Deficiency leads to **Pellagra**, characterized by the 3 Ds: Dermatitis, Diarrhea, and Dementia. * **Riboflavin (B2):** Deficiency presents with Cheilosis, glossitis, and corneal neovascularization (the "2 Cs" of B2). **High-Yield NEET-PG Pearls:** * **Enzyme Marker:** Erythrocyte **transketolase** activity (decreased in thiamine deficiency) is the gold standard for diagnosis. * **Wernicke’s Triad:** Confusion, Ataxia, Ophthalmoplegia. * **Korsakoff Syndrome:** Irreversible amnesia and **confabulation** (making up stories) due to damage to the mammillary bodies. * **Clinical Rule:** Always administer thiamine *before* glucose in malnourished/alcoholic patients to prevent precipitating Wernicke encephalopathy.

Q: Collagen formation is affected in the deficiency of which vitamin?

Vitamin C. **Explanation:** **Vitamin C (Ascorbic Acid)** is the correct answer because it serves as a vital co-factor for the post-translational modification of collagen. Specifically, it is required by the enzymes **prolyl hydroxylase** and **lysyl hydroxylase**. These enzymes hydroxylate proline and lysine residues in the pro-alpha chains of collagen. This hydroxylation is essential for: 1. **Hydrogen bond formation:** Which stabilizes the triple helix structure of collagen. 2. **Cross-linking:** Which provides tensile strength to the connective tissue. In the absence of Vitamin C, the collagen produced is under-hydroxylated and unstable, leading to the clinical manifestation of **Scurvy** (characterized by capillary fragility, bruising, and poor wound healing). **Why other options are incorrect:** * **Vitamin A:** Primarily involved in vision (rhodopsin cycle), epithelial cell differentiation, and immune function. * **Vitamin B2 (Riboflavin):** Functions as a precursor for FAD and FMN, which are essential for redox reactions in the TCA cycle and Electron Transport Chain. * **Vitamin D:** Regulates calcium and phosphate metabolism and is essential for bone mineralization (deficiency leads to Rickets or Osteomalacia), but it does not directly mediate collagen synthesis. **High-Yield Clinical Pearls for NEET-PG:** * **Enzyme Mechanism:** Vitamin C keeps the iron cofactor of hydroxylase enzymes in the reduced **ferrous (Fe²⁺) state**. * **Scurvy Symptoms:** "Corkscrew hair," perifollicular hemorrhages, and swollen, bleeding gums. * **Wound Healing:** Collagen is the primary protein involved in the proliferative phase of wound healing; thus, Vitamin C deficiency significantly delays recovery.

Question 1

Which vitamin deficiency can cause rickets?

Accepted Answer

Vitamin D

Answer

Vitamin C

Answer

Niacin

Answer

Biotin

Question 2

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 3

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 4

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

Accepted Answer

Transketolase

Answer

Transaldolase

Answer

Alpha ketoglutarate dehydrogenase

Answer

Pyruvate dehydrogenase

Question 5

Which of the following is the synthetic vitamer of vitamin K?

Accepted Answer

Menadione

Answer

Phylloquinone

Answer

Menaquinone

Answer

All of the above

Question 6

Deficiency of which vitamin causes spinocerebellar ataxia?

Accepted Answer

Vitamin E

Answer

Vitamin B12

Answer

Vitamin C

Answer

Vitamin A

Question 7

The given condition is caused due to deficiency of which of the following?

Accepted Answer

Zinc

Answer

Niacin

Answer

Iron

Answer

Selenium

Question 8

A constellation of neuropathy, muscle weakness and wasting, cardiomegaly, edema, and ophthalmoplegia strongly suggests which of the following deficiencies?

Accepted Answer

Thiamine deficiency

Answer

Cobalamin deficiency

Answer

Niacin deficiency

Answer

Riboflavin deficiency

Question 9

Thiamine status of an individual can be detected by which of the following tests/enzymes in erythrocytes?

Accepted Answer

Transketolase

Answer

Transaldolase

Answer

Glucose-6-phosphatase

Answer

Enolase

Question 10

Collagen formation is affected in the deficiency of which vitamin?

Accepted Answer

Vitamin C

Answer

Vitamin A

Answer

Vitamin B2

Answer

Vitamin D

Vitamins and Coenzymes — MCQs

Vitamins and Coenzymes — MCQs

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