Vitamins and Coenzymes Practice Questions

Q: All are diagnostic features of osteomalacia except?

Increased serum calcium. **Explanation:** Osteomalacia is characterized by impaired mineralization of the bone matrix (osteoid) in adults, most commonly due to **Vitamin D deficiency**. **1. Why "Increased serum calcium" is the correct answer:** In osteomalacia, serum calcium is typically **low or low-normal**, never increased. Vitamin D deficiency leads to decreased intestinal absorption of calcium. This triggers secondary hyperparathyroidism (increased PTH) to maintain calcium levels by mobilizing it from bones, but the net result is still a state of calcium deficit. Hypercalcemia would point toward primary hyperparathyroidism or malignancy, not osteomalacia. **2. Analysis of other options:** * **Increased alkaline phosphatase (ALP):** This is a classic finding. Increased osteoblastic activity (an attempt to form new bone) results in elevated serum ALP levels. * **Proximal myopathy:** Vitamin D is essential for muscle function. Deficiency leads to "waddling gait" and proximal muscle weakness, a hallmark clinical feature of osteomalacia. * **Looser’s zones:** Also known as pseudofractures or Milkman’s lines, these are radiolucent bands representing unmineralized osteoid at sites of stress (e.g., femoral neck, ribs). They are **pathognomonic** for osteomalacia. **3. NEET-PG High-Yield Pearls:** * **Biochemical Profile:** ↓/Normal Calcium, ↓ Phosphate (due to PTH-induced renal wasting), ↑ PTH, and ↑ ALP. * **Radiology:** Look for "Codfish vertebrae" (biconcave) and Looser's zones. * **Histology:** The gold standard (though rarely done) shows an **increased thickness of osteoid seams**. * **Rickets vs. Osteomalacia:** Rickets occurs before epiphyseal closure (children); Osteomalacia occurs after (adults).

Q: Barlow's syndrome is due to deficiency of which vitamin?

Vitamin C. **Explanation:** **Barlow’s syndrome** is the clinical term for **infantile scurvy**, which results from a deficiency of **Vitamin C (Ascorbic acid)**. Vitamin C is a critical cofactor for the enzymes *prolyl hydroxylase* and *lysyl hydroxylase*. These enzymes are responsible for the hydroxylation of proline and lysine residues during collagen synthesis. Without Vitamin C, defective collagen formation leads to weakened connective tissues, fragile blood vessels (causing subperiosteal hemorrhages), and impaired bone matrix formation. In infants, this manifests as painful limb swelling (pseudoparalysis) and a "scorbutic rosary" at the costochondral junctions. **Analysis of Incorrect Options:** * **Vitamin E:** Deficiency typically leads to hemolytic anemia, posterior column signs (ataxia, loss of proprioception), and retinal degeneration, but not bone or collagen defects. * **Vitamin B6 (Pyridoxine):** Deficiency causes peripheral neuropathy, sideroblastic anemia, and seborrheic dermatitis. It is also associated with isoniazid (INH) therapy. * **Vitamin B1 (Thiamine):** Deficiency leads to Beriberi (Dry or Wet) and Wernicke-Korsakoff syndrome, primarily affecting the cardiovascular and nervous systems. **High-Yield Clinical Pearls for NEET-PG:** * **Radiological Signs of Scurvy:** Look for **Frankel’s line** (dense zone of provisional calcification), **Wimberger’s ring** (sclerotic margin around epiphysis), and **Pelkan spurs**. * **Barlow’s Disease vs. Barlow’s Syndrome:** Do not confuse *Barlow’s Disease* (Infantile Scurvy) with *Barlow’s Syndrome* (Mitral Valve Prolapse), though in many medical entrance contexts, the term is used synonymously with Vitamin C deficiency. * Vitamin C also enhances **iron absorption** by maintaining it in the ferrous ($Fe^{2+}$) state.

Q: Magenta coloured tongue is seen in deficiency of which vitamin?

Riboflavin. **Explanation:** The correct answer is **Riboflavin (Vitamin B2)**. **1. Why Riboflavin is correct:** Riboflavin is a precursor for the coenzymes **FMN** and **FAD**, which are essential for oxidation-reduction reactions. A deficiency of Vitamin B2 leads to a clinical constellation known as **Ariboflavinosis**. The hallmark sign is a **magenta-colored tongue**, which occurs due to inflammation (glossitis) and vascular changes in the lingual papillae. Other classic features include **cheilosis** (fissuring at the corners of the mouth), **angular stomatitis**, and **corneal neovascularization**. **2. Why other options are incorrect:** * **Niacin (B3):** Deficiency causes **Pellagra**, characterized by the 4 Ds (Dermatitis, Diarrhea, Dementia, and Death). The tongue in Pellagra is typically described as **"Beefy Red"** or "Scarlet," not magenta. * **Vitamin B12 (Cobalamin):** Deficiency leads to Megaloblastic anemia and Subacute Combined Degeneration of the spinal cord. The tongue appears **smooth, pale, and shiny** (Hunter’s glossitis or Atrophic glossitis) due to the loss of papillae. **3. NEET-PG High-Yield Pearls:** * **Riboflavin** is light-sensitive; phototherapy for neonatal jaundice can lead to its deficiency. * **Glutathione Reductase test:** The gold standard for diagnosing B2 deficiency is measuring the activity of erythrocyte glutathione reductase. * **Mnemonic for B2:** The "2s" — Vitamin **B2**, affects **2** C's (Cheilosis and Corneal vascularization), and results in a **Magenta** tongue (M is the 13th letter, 1+3=4, which is 2 squared). * **B3 vs. B2 Tongue:** Remember **B3 = Beefy Red**, **B2 = Magenta**.

Q: Megaloblastic anaemia occurs due to which of the following deficiencies?

Folate deficiency. **Explanation:** **Megaloblastic anemia** is a type of macrocytic anemia characterized by the presence of large, nucleated red blood cell precursors (megaloblasts) in the bone marrow. The underlying mechanism is **impaired DNA synthesis** while RNA and protein synthesis remain intact, leading to "nuclear-cytoplasmic asynchrony." **Why Folate deficiency is correct:** Folate (Vitamin B9) is essential for the synthesis of **thymidine**, one of the four bases in DNA. Specifically, tetrahydrofolate (THF) acts as a one-carbon donor in the conversion of dUMP to dTMP. When folate is deficient, DNA replication is hindered, causing cells to grow in size without dividing, resulting in macrocytosis and megaloblastic changes. (Note: Vitamin B12 deficiency also causes megaloblastic anemia via the "folate trap" mechanism). **Why other options are incorrect:** * **Iron deficiency:** Causes **microcytic hypochromic anemia** due to impaired hemoglobin synthesis. * **Vitamin C deficiency:** Leads to **Scurvy**. While Vitamin C aids iron absorption, its primary deficiency does not characteristically cause megaloblastic anemia. * **Protein deficiency:** Associated with **Kwashiorkor**, which typically presents with normocytic anemia due to overall reduced erythropoiesis. **NEET-PG High-Yield Pearls:** 1. **The Folate Trap:** B12 deficiency leads to a functional folate deficiency because folate becomes "trapped" as N5-methyl THF, which cannot be converted back to the active THF form. 2. **Diagnostic Marker:** Hypersegmented neutrophils (≥ 5 lobes) on a peripheral smear are the earliest sign of megaloblastic anemia. 3. **Differentiating B12 vs. Folate:** B12 deficiency presents with **neurological symptoms** (Subacute Combined Degeneration of the spinal cord) and elevated **Methylmalonic Acid (MMA)** levels, whereas folate deficiency does not.

Q: A 45-year-old diabetic patient presents with hypertriglyceridemia and elevated LDL. Which of the following vitamins can be indicated in this patient?

Niacin. **Explanation:** **Correct Option: C (Niacin/Vitamin B3)** Niacin, specifically in the form of nicotinic acid, is used pharmacologically to treat dyslipidemia. It acts by inhibiting the enzyme **hormone-sensitive lipase** in adipose tissue, which reduces the breakdown of triglycerides into free fatty acids (FFAs). Since fewer FFAs reach the liver, there is a decreased synthesis of VLDL, which subsequently leads to **lower levels of LDL and triglycerides**. Additionally, Niacin is the most potent vitamin for **increasing HDL levels** by inhibiting the hepatic uptake of Apolipoprotein A-I. **Why other options are incorrect:** * **A. Thiamine (B1):** Primarily acts as a coenzyme for oxidative decarboxylation (e.g., Pyruvate Dehydrogenase). Deficiency leads to Beriberi or Wernicke-Korsakoff syndrome, but it has no lipid-lowering properties. * **B. Riboflavin (B2):** Precursor for FAD and FMN, involved in redox reactions. It does not influence plasma lipid profiles. * **D. Pantothenic acid (B5):** A constituent of Coenzyme A (CoA). While CoA is essential for fatty acid metabolism, B5 supplementation is not a clinical treatment for hyperlipidemia. **High-Yield NEET-PG Pearls:** * **Side Effects:** The most common side effect of Niacin is **cutaneous flushing**, mediated by Prostaglandin D2/E2 (can be prevented by Aspirin). * **Metabolic Risks:** Niacin can cause **hyperuricemia** (precipitating gout) and **hyperglycemia** (use with caution in diabetics, though still indicated for severe dyslipidemia). * **Key Enzyme:** Niacin inhibits **Diacylglycerol acyltransferase-2 (DGAT-2)** in the liver, further reducing triglyceride synthesis.

Q: Dermatitis and alopecia are due to deficiency of which micronutrient?

Zinc. **Explanation:** **Zinc** is an essential trace element that serves as a cofactor for over 300 enzymes, including those involved in DNA synthesis, protein metabolism, and cell division. It is particularly crucial for rapidly dividing cells like those in the skin and hair follicles. * **Why Zinc is correct:** Zinc deficiency leads to impaired keratinization and wound healing. The classic clinical triad of zinc deficiency includes **acrodermatitis enteropathica** (periorificial and acral dermatitis), **alopecia**, and **diarrhea**. It is also associated with growth retardation, hypogonadism, and impaired night vision (as it is a cofactor for retinol dehydrogenase). **Analysis of Incorrect Options:** * **Molybdenum:** This is a cofactor for enzymes like xanthine oxidase and sulfite oxidase. Deficiency is extremely rare but typically presents with neurological symptoms and lens dislocation, not dermatological issues. * **Magnesium:** Primarily involved in neuromuscular transmission and ATP-dependent enzymatic reactions. Deficiency (hypomagnesemia) leads to neuromuscular irritability, tetany, and arrhythmias. * **Calcium:** Essential for bone mineralization, blood coagulation, and muscle contraction. Deficiency leads to rickets/osteomalacia and tetany. **High-Yield Clinical Pearls for NEET-PG:** * **Acrodermatitis Enteropathica:** An autosomal recessive disorder causing impaired intestinal zinc absorption. * **Zinc & Wound Healing:** Zinc is a cofactor for **Matrix Metalloproteinases (MMPs)**, which are essential for collagen remodeling. * **Diagnosis:** Low serum alkaline phosphatase levels can sometimes be a clue to zinc deficiency, as the enzyme is zinc-dependent.

Q: Carboxylases require which vitamin as a coenzyme?

Vitamin B7 (Biotin). **Explanation:** **Vitamin B7 (Biotin)** is the essential coenzyme for all major **carboxylase enzymes** in the body. It acts as a carrier of activated carbon dioxide (CO₂), facilitating the addition of a carboxyl group to various substrates. Biotin is covalently bound to the enzyme via a lysine residue, forming a "biotinyl-lysine" (biocytin) complex. **Key Carboxylases requiring Biotin:** 1. **Pyruvate Carboxylase:** Converts pyruvate to oxaloacetate (Gluconeogenesis). 2. **Acetyl-CoA Carboxylase:** Converts Acetyl-CoA to Malonyl-CoA (Fatty acid synthesis). 3. **Propionyl-CoA Carboxylase:** Converts Propionyl-CoA to Methylmalonyl-CoA (Odd-chain fatty acid metabolism). **Why other options are incorrect:** * **Vitamin B2 (Riboflavin):** Functions as a precursor for FAD and FMN, which are involved in **Oxidation-Reduction (Redox)** reactions (e.g., Succinate dehydrogenase). * **Vitamin B12 (Cobalamin):** Acts as a coenzyme for **Methylmalonyl-CoA mutase** and **Methionine synthase**. It is involved in isomerisation and methylation, not carboxylation. * **Vitamin B1 (Thiamine):** As Thiamine Pyrophosphate (TPP), it is a cofactor for **Oxidative Decarboxylation** (e.g., Pyruvate dehydrogenase) and Transketolase reactions. **High-Yield Clinical Pearls for NEET-PG:** * **Egg White Injury:** Raw egg whites contain **Avidin**, a protein that binds biotin with high affinity, preventing its absorption and leading to deficiency. * **Biotinidase Deficiency:** An autosomal recessive metabolic disorder that prevents the recycling of biotin, leading to neurological symptoms and dermatitis. * **The "ABC" Rule:** Carboxylases typically require **A**TP, **B**iotin, and **C**O₂.

Q: Vitamin B12 and folic acid supplementation in megaloblastic anemia leads to the improvement of anemia due to which of the following mechanisms?

Increased DNA synthesis in bone marrow. **Explanation:** The hallmark of megaloblastic anemia is **impaired DNA synthesis** with preserved RNA and protein synthesis, leading to "nuclear-cytoplasmic asynchrony." **Why Option A is Correct:** Vitamin B12 (Cobalamin) and Folic acid are essential cofactors for DNA synthesis. Vitamin B12 acts as a cofactor for *Methionine Synthase*, which converts homocysteine to methionine. During this reaction, **N5-methyltetrahydrofolate** is converted back to **Tetrahydrofolate (THF)**. THF is then converted to N5,N10-methylene THF, a crucial donor for the conversion of dUMP to dTMP (catalyzed by *Thymidylate Synthase*). Without B12 or Folate, thymidine production halts, DNA replication is inhibited, and hematopoiesis becomes ineffective. Supplementation restores this pathway, allowing rapid DNA synthesis and normal erythrocyte maturation in the bone marrow. **Why Other Options are Incorrect:** * **Option B:** Hemoglobin production is primarily dependent on iron and globin chain synthesis. This is the mechanism for treating Iron Deficiency Anemia, not megaloblastic anemia. * **Option C:** Erythroid hyperplasia is a *feature* of the bone marrow's compensatory response to anemia, but it is not the *mechanism* of improvement. In fact, supplementation resolves the ineffective erythropoiesis. * **Option D:** Iron absorption is unrelated to the primary defect in B12/Folate deficiency. **High-Yield NEET-PG Pearls:** * **Folate Trap Hypothesis:** B12 deficiency "traps" folate in the N5-methyl THF form, leading to a functional folate deficiency. * **Neurological Symptoms:** Only B12 deficiency causes Subacute Combined Degeneration (SCD) of the spinal cord due to impaired myelin synthesis (via Methylmalonyl-CoA Mutase). * **Diagnostic Marker:** Elevated **Methylmalonic Acid (MMA)** is specific for B12 deficiency, whereas **Homocysteine** is elevated in both B12 and Folate deficiency.

Question 1

All are diagnostic features of osteomalacia except?

Accepted Answer

Increased serum calcium

Answer

Increased alkaline phosphatase

Answer

Proximal myopathy

Answer

Looser's zone

Question 2

Barlow's syndrome is due to deficiency of which vitamin?

Accepted Answer

Vitamin C

Answer

Vitamin E

Answer

Vitamin B6

Answer

Vitamin B1

Question 3

Magenta coloured tongue is seen in deficiency of which vitamin?

Accepted Answer

Riboflavin

Answer

Niacin

Answer

Vitamin B12

Answer

All of the above

Question 4

Megaloblastic anaemia occurs due to which of the following deficiencies?

Accepted Answer

Folate deficiency

Answer

Iron deficiency

Answer

Vitamin C deficiency

Answer

Protein deficiency

Question 5

A 45-year-old diabetic patient presents with hypertriglyceridemia and elevated LDL. Which of the following vitamins can be indicated in this patient?

Accepted Answer

Niacin

Answer

Thiamine

Answer

Riboflavin

Answer

Pantothenic acid

Question 6

Increase in pyruvate and lactate levels is seen in which of the following vitamin deficiencies?

Accepted Answer

Thiamine

Answer

Pyridoxine

Answer

Niacin

Answer

Vitamin C

Question 7

Which of the following vitamins deficiency occurs exclusively in carnivores?

Accepted Answer

Vitamin C

Answer

Thiamine

Answer

Niacin

Answer

Cobalamine

Question 8

Dermatitis and alopecia are due to deficiency of which micronutrient?

Accepted Answer

Zinc

Answer

Molybdenum

Answer

Magnesium

Answer

Calcium

Question 9

Carboxylases require which vitamin as a coenzyme?

Accepted Answer

Vitamin B7 (Biotin)

Answer

Vitamin B2 (Riboflavin)

Answer

Vitamin B12 (Cobalamin)

Answer

Vitamin B1 (Thiamine)

Question 10

Vitamin B12 and folic acid supplementation in megaloblastic anemia leads to the improvement of anemia due to which of the following mechanisms?

Accepted Answer

Increased DNA synthesis in bone marrow

Answer

Increased hemoglobin production

Answer

Erythroid hyperplasia

Answer

Increased iron absorption

Vitamins and Coenzymes — MCQs

Vitamins and Coenzymes — MCQs

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