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: 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: 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: Yellowing of the skin occurs in hypothyroidism because of which of the following?

Increased carotene. **Explanation:** In hypothyroidism, the yellowing of the skin is primarily due to **Hypercarotenemia**. Thyroid hormones are essential for the hepatic conversion of dietary beta-carotene into Vitamin A (Retinol) [1]. In a hypothyroid state, this enzymatic conversion is impaired, leading to an accumulation of carotene in the serum and its subsequent deposition in the stratum corneum of the skin. **Analysis of Options:** * **A. Increased bilirubin:** While jaundice (hyperbilirubinemia) causes yellowing, it typically involves the **sclera** (icterus). In hypothyroidism, the yellowing spares the sclera, distinguishing it from liver disease. * **B. Increased cholesterol:** Hypothyroidism does cause hypercholesterolemia (due to decreased LDL receptor expression [2]), but cholesterol itself does not impart a yellow pigment to the skin. * **C. Increased carotene (Correct):** The lack of thyroxine prevents the breakdown of carotene, leading to "Carotenemic xanthoderma." * **D. Increased levels of thyroid hormones:** This describes hyperthyroidism, which is associated with warm, moist, and often flushed skin, not yellowing. **High-Yield Clinical Pearls for NEET-PG:** * **Scleral Sparing:** Carotenemia (hypothyroidism) causes yellowing of the palms and soles but **never** the sclera. Jaundice **always** involves the sclera. * **Vitamin A Connection:** Hypothyroidism can lead to functional Vitamin A deficiency despite high carotene levels because the conversion process is blocked [1]. * **Skin Texture:** The skin in hypothyroidism is classically described as **"Cold, Dry, and Coarse"** with non-pitting edema (Myxedema) due to the accumulation of glycosaminoglycans (hyaluronic acid) in the dermis.

Q: Xerosis/Xerophthalmia is due to deficiency of:

Vitamin A. **Explanation:** **Vitamin A (Retinol)** is essential for maintaining the integrity of epithelial tissues throughout the body. In the eye, it plays a critical role in the health of the conjunctiva and cornea. Vitamin A deficiency leads to a loss of mucus-secreting goblet cells, resulting in **squamous metaplasia** and keratinization of the ocular surface. This process causes the dryness and thickening characteristic of **Xerophthalmia** (literally "dry eye"). **Why the other options are incorrect:** * **Vitamin K:** Primarily functions as a cofactor for the gamma-carboxylation of clotting factors (II, VII, IX, X). Deficiency leads to bleeding diathesis and increased PT/INR. * **Vitamin E:** Acts as a potent lipid-soluble antioxidant, protecting cell membranes from free radical damage. Deficiency typically manifests as hemolytic anemia, posterior column signs, or ataxia. * **Vitamin D:** Regulates calcium and phosphate homeostasis. Deficiency leads to Rickets in children and Osteomalacia in adults. **High-Yield Clinical Pearls for NEET-PG:** * **WHO Classification of Xerophthalmia:** * **X1A:** Conjunctival xerosis (earliest sign). * **X1B:** **Bitot’s Spots** (triangular, foamy patches on the bulbar conjunctiva). * **X2:** Corneal xerosis. * **X3A/X3B:** Keratomalacia (corneal melting/liquefaction; the most serious stage). * **Night Blindness (Nyctalopia):** The earliest clinical symptom of Vitamin A deficiency due to impaired regeneration of **Rhodopsin** in the rods. * **All-trans retinoic acid (ATRA):** Used in the treatment of Acute Promyelocytic Leukemia (APML/M3).

Q: Which of the following is a constituent of vitamin B12?

Cobalt. **Explanation:** **Vitamin B12 (Cobalamin)** is unique among vitamins because it contains a metal ion as an integral part of its structure. The core of the molecule consists of a **corrin ring** (similar to the porphyrin ring in heme) with a **Cobalt** atom at its center. This is why the chemical name for Vitamin B12 is **Cyanocobalamin** (or Hydroxocobalamin/Methylcobalamin). Cobalt is essential for the vitamin’s biological activity, specifically in the transfer of methyl groups and DNA synthesis. **Why other options are incorrect:** * **Iodine:** Primarily required for the synthesis of thyroid hormones (T3 and T4) in the thyroid gland. * **Zinc:** Acts as a cofactor for over 300 enzymes, including Carbonic Anhydrase, Alcohol Dehydrogenase, and DNA polymerase, but is not part of B12. * **Iron:** The central metal ion in the **Heme** group of hemoglobin, myoglobin, and cytochromes. **High-Yield Clinical Pearls for NEET-PG:** * **Sources:** Vitamin B12 is synthesized exclusively by microorganisms; it is **not found in plant foods**, making vegans a high-risk group for deficiency. * **Absorption:** Requires **Intrinsic Factor (IF)** secreted by gastric parietal cells. Absorption occurs in the **terminal ileum**. * **Storage:** Unlike other water-soluble vitamins, B12 is stored in the **liver** for 3–5 years. * **Deficiency:** Leads to **Megaloblastic Anemia** and neurological symptoms (Subacute Combined Degeneration of the spinal cord) due to the accumulation of Methylmalonic Acid (MMA). * **Key Reactions:** It is a coenzyme for two major reactions: 1. Methionine synthase (Homocysteine → Methionine). 2. Methylmalonyl-CoA mutase (Proprionyl-CoA metabolism).

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

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 4

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 5

Which of the following vitamins deficiency occurs exclusively in carnivores?

Accepted Answer

Vitamin C

Answer

Thiamine

Answer

Niacin

Answer

Cobalamine

Question 6

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 7

Which of the following nutritional factors is required for proper collagen assembly in scar tissue?

Accepted Answer

Vitamin C

Answer

Folic acid

Answer

Thiamine

Answer

Vitamin A

Question 8

Yellowing of the skin occurs in hypothyroidism because of which of the following?

Accepted Answer

Increased carotene

Answer

Increased bilirubin

Answer

Increased cholesterol

Answer

Increased levels of thyroid hormones

Question 9

Xerosis/Xerophthalmia is due to deficiency of:

Accepted Answer

Vitamin A

Answer

Vitamin K

Answer

Vitamin E

Answer

Vitamin D

Question 10

Which of the following is a constituent of vitamin B12?

Accepted Answer

Cobalt

Answer

Iodine

Answer

Zinc

Answer

Iron

Vitamins and Coenzymes — MCQs

Vitamins and Coenzymes — MCQs

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