Vitamins and Coenzymes Practice Questions

Q: Which of the following is NOT seen in vitamin A deficiency?

Polyneuritis. **Explanation:** The correct answer is **D. Polyneuritis**. **Why Polyneuritis is the correct choice:** Polyneuritis (inflammation of multiple peripheral nerves) is a classic manifestation of **Vitamin B1 (Thiamine) deficiency**, specifically seen in Dry Beriberi. Vitamin A (Retinol) is primarily involved in vision, epithelial integrity, and immune function; it does not play a direct role in peripheral nerve maintenance. Therefore, polyneuritis is not a feature of Vitamin A deficiency. **Analysis of incorrect options:** * **A. Night Blindness (Nyctalopia):** This is the earliest symptom of Vitamin A deficiency. Retinol is essential for the synthesis of **rhodopsin** (visual purple) in the rod cells of the retina, which are responsible for vision in dim light. * **B. Follicular Hyperkeratosis:** Vitamin A is vital for maintaining epithelial tissues. Deficiency leads to keratinization of the skin, resulting in a rough, "gooseflesh" appearance known as **Phrynoderma** (toad skin). * **C. Growth Retardation:** Vitamin A is essential for skeletal growth and cell differentiation. It acts like a hormone (via Retinoic Acid receptors) to regulate gene expression necessary for bone remodeling and protein synthesis. **High-Yield Clinical Pearls for NEET-PG:** * **WHO Classification of Xerophthalmia:** X1A (Conjunctival xerosis), X1B (**Bitot’s spots** - triangular pearly white foamy spots), X2 (Corneal xerosis), X3A/B (Keratomalacia/Corneal liquefaction). * **Earliest Sign:** Conjunctival xerosis. * **Earliest Symptom:** Night blindness. * **Hypervitaminosis A:** Can cause pseudotumor cerebri (increased intracranial pressure) and is highly teratogenic (avoid in pregnancy).

Q: Bald tongue is seen in deficiency of which vitamin?

Niacin. **Explanation:** **Bald tongue** (atrophic glossitis) is a clinical condition characterized by the loss of filiform papillae, making the tongue appear smooth, red, and "bald." **Why Niacin (Vitamin B3) is the correct answer:** Niacin deficiency leads to **Pellagra**, classically characterized by the **4 Ds**: Dermatitis, Diarrhea, Dementia, and Death. A hallmark oral manifestation of Pellagra is a bright red, swollen, and "bald" tongue (glossitis). This occurs because Niacin (as NAD/NADP) is essential for rapid cell turnover; its deficiency impairs the regeneration of the lingual epithelium, leading to papillary atrophy. **Analysis of Incorrect Options:** * **Riboflavin (B2):** Deficiency typically presents with **Magenta tongue** (purplish-red hue), angular stomatitis, and cheilosis. While glossitis occurs, the "bald" description is more classic for Niacin or B12. * **Vitamin B12:** Deficiency causes **Hunter’s glossitis** or Moeller’s glossitis. While the tongue appears smooth and red (bald), in the context of standard NEET-PG patterns, Niacin is the primary association for the specific term "Bald tongue" related to Pellagra, whereas B12 is often linked to "Beefy red tongue." **High-Yield Clinical Pearls for NEET-PG:** * **Casal’s Necklace:** Hyperpigmented rash around the neck seen in Niacin deficiency. * **Hartnup Disease:** An autosomal recessive disorder involving impaired tryptophan transport, leading to secondary Niacin deficiency and Pellagra-like symptoms. * **Tryptophan Connection:** 60 mg of dietary Tryptophan is required to synthesize 1 mg of Niacin. * **Carcinoid Syndrome:** Can lead to Niacin deficiency because tryptophan is diverted to produce excessive Serotonin.

Q: Which of the following combinations of biologically active molecules does vitamin A consist of?

Retinol, retinal, and retinoic acid. **Explanation:** Vitamin A (Retinoids) refers to a group of biologically active polyisoprenoid compounds. The correct answer is **Option A** because Vitamin A exists in three primary active forms in the body, often referred to as the "retinoid family": 1. **Retinol:** The alcohol form, primarily used for storage (as retinyl esters) and transport. 2. **Retinal (Retinaldehyde):** The aldehyde form, essential for the visual cycle (specifically 11-cis retinal). 3. **Retinoic Acid:** The acid form, which acts as a hormone to regulate gene expression, epithelial cell differentiation, and growth. **Analysis of Incorrect Options:** * **Option B:** Includes **Tetrahydrofolate (THF)**, which is the active coenzyme form of Vitamin B9 (Folic acid), not Vitamin A. * **Option C:** Mentions **Conjugase**, which is an enzyme involved in the intestinal absorption of Folate (polyglutamate to monoglutamate conversion), not a component of Vitamin A. * **Option D:** Includes **PABA (Para-aminobenzoic acid)**, which is a structural component of Folic acid. It also lists "retinal" and "retinaldehyde" twice, as they are synonyms. **High-Yield NEET-PG Pearls:** * **Visual Cycle (Wald’s Cycle):** 11-cis retinal combines with opsin to form rhodopsin. Light causes isomerization to all-trans retinal. * **Storage:** Vitamin A is stored in the liver (Ito cells) as **Retinyl palmitate**. * **Teratogenicity:** Retinoic acid is highly teratogenic; pregnancy must be excluded before prescribing Isotretinoin for acne. * **Deficiency:** The earliest symptom is Nyctalopia (night blindness); the earliest physical sign is Conjunctival Xerosis. Bitot’s spots are a pathognomonic sign.

Q: Pyridoxine is essential for the generation of which coenzyme?

NAD (Nicotinamide Adenine Dinucleotide). **Explanation:** The correct answer is **NAD (Nicotinamide Adenine Dinucleotide)** because Pyridoxine (Vitamin B6) plays a crucial role in the **Kynurenine pathway**, which converts the amino acid Tryptophan into Niacin (Vitamin B3). Specifically, the enzyme **Kynureninase** is dependent on **Pyridoxal Phosphate (PLP)**, the active form of Vitamin B6. If B6 is deficient, the conversion of Tryptophan to Niacin is impaired, leading to a decrease in the synthesis of NAD and NADP. **Analysis of Options:** * **Option A (FAD):** This is derived from **Riboflavin (Vitamin B2)**. While B2 is also required in the Kynurenine pathway (for Kynurenine hydroxylase), FAD itself is not generated from Pyridoxine. * **Option B (ATP):** ATP is the primary energy currency of the cell, synthesized via oxidative phosphorylation and substrate-level phosphorylation. It is not a derivative of Pyridoxine. * **Option D:** Incorrect, as the biochemical link between B6 and NAD synthesis is well-established. **Clinical Pearls for NEET-PG:** * **Pellagra-like symptoms:** A deficiency in Vitamin B6 can manifest as secondary Niacin deficiency (Pellagra) because of the failed conversion of Tryptophan to NAD. * **Isoniazid (INH) Therapy:** This anti-tubercular drug is a structural analog of B6. It inhibits the formation of PLP, leading to peripheral neuropathy and potentially Pellagra-like symptoms. Always co-administer B6 with INH. * **Rule of 60:** Approximately **60 mg of Tryptophan** is required to synthesize **1 mg of Niacin**. * **Hartnup Disease:** A defect in neutral amino acid (Tryptophan) transporters can also lead to NAD deficiency, mimicking B6/B3 deficiency.

Q: Which vitamin is essential for both bone formation and the coagulation cascade?

Vitamin K. **Explanation:** **Vitamin K** is the correct answer because it serves as an essential cofactor for the enzyme **$\gamma$-glutamyl carboxylase**. This enzyme catalyzes the post-translational carboxylation of glutamate residues into $\gamma$-carboxyglutamate (Gla) on specific proteins, allowing them to bind calcium. 1. **Coagulation Cascade:** Vitamin K is required for the activation of Clotting Factors **II, VII, IX, and X**, as well as anticoagulant proteins C and S. 2. **Bone Formation:** It is essential for the carboxylation of **Osteocalcin** (Bone Gla Protein) and **Matrix Gla Protein**. Carboxylated osteocalcin has a high affinity for hydroxyapatite, facilitating calcium deposition in the bone matrix. **Analysis of Incorrect Options:** * **Vitamin A:** Primarily involved in vision (rhodopsin), epithelial differentiation, and immune function. While it affects bone remodeling, it is not a cofactor for the coagulation cascade. * **Vitamin D:** Crucial for calcium homeostasis and bone mineralization by increasing intestinal calcium absorption, but it plays no direct role in the enzymatic activation of clotting factors. * **Vitamin E:** Acts as a potent lipid-soluble antioxidant. High doses can actually *interfere* with Vitamin K metabolism, potentially increasing bleeding risk. **High-Yield NEET-PG Pearls:** * **Warfarin Mechanism:** Inhibits **Vitamin K Epoxide Reductase (VKOR)**, preventing the recycling of Vitamin K and thus inhibiting the carboxylation of factors II, VII, IX, and X. * **Newborns:** They are born with sterile guts and low Vitamin K stores; hence, a prophylactic IM injection of Vitamin K is given to prevent **Hemorrhagic Disease of the Newborn**. * **Lab Marker:** Prothrombin Time (PT) is the most sensitive lab test to monitor Vitamin K deficiency.

Q: Which test is used to diagnose thiamine deficiency?

RBC transketolase. **Explanation:** **Correct Option: A. RBC transketolase** Thiamine (Vitamin B1) acts as a coenzyme in the form of **Thiamine Pyrophosphate (TPP)**. It is a critical cofactor for the enzyme **Transketolase** in the Pentose Phosphate Pathway (HMP Shunt). The gold standard biochemical test for diagnosing thiamine deficiency is measuring the **Erythrocyte (RBC) Transketolase activity**. * **The Concept:** If activity increases by >15–25% after adding exogenous TPP in vitro (TPP effect), it confirms a deficiency. **Incorrect Options:** * **B & D. FIGLU excretion / Histidine load test:** These tests are used to diagnose **Folic acid (Vitamin B9) deficiency**. Formiminoglutamic acid (FIGLU) is an intermediate in histidine metabolism; its conversion to glutamate requires THF. In B9 deficiency, FIGLU is excreted in excess in urine. * **C. Methyl-malonic acid (MMA) in urine:** This is the specific marker for **Vitamin B12 (Cobalamin) deficiency**. B12 is a cofactor for Methylmalonyl-CoA mutase; without it, MMA levels rise in the blood and urine. **High-Yield Clinical Pearls for NEET-PG:** * **Key TPP-dependent enzymes:** Pyruvate Dehydrogenase (PDH), $\alpha$-Ketoglutarate Dehydrogenase, and Transketolase. * **Clinical Triad of Wernicke’s Encephalopathy:** Ataxia, Ophthalmoplegia, and Confusion. * **Wet Beriberi:** Thiamine deficiency presenting with high-output heart failure and edema. * **Dry Beriberi:** Presents as peripheral neuropathy. * **Rule of Thumb:** Always give Thiamine *before* Glucose in a malnourished/alcoholic patient to prevent precipitating Wernicke’s (as glucose oxidation consumes remaining TPP).

Q: Decarboxylation reactions require which of the following vitamins as a coenzyme?

Thiamine. **Explanation:** The correct answer is **Thiamine (Vitamin B1)**. Thiamine, in its active form **Thiamine Pyrophosphate (TPP)**, serves as a vital coenzyme for oxidative decarboxylation reactions. It acts as a carrier of "active aldehyde" groups, facilitating the removal of carboxyl groups from α-keto acids. Key enzymes requiring TPP include: 1. **Pyruvate Dehydrogenase (PDH):** Converts pyruvate to acetyl-CoA. 2. **α-Ketoglutarate Dehydrogenase:** A crucial step in the TCA cycle. 3. **Branched-chain α-keto acid dehydrogenase:** Involved in the metabolism of Leucine, Isoleucine, and Valine. **Analysis of Incorrect Options:** * **Riboflavin (B2):** Functions as FAD/FMN, primarily involved in **Redox (oxidation-reduction) reactions** (e.g., Succinate dehydrogenase). * **Niacin (B3):** Functions as NAD/NADP, also involved in **Redox reactions** as an electron carrier. * **Biotin (B7):** Functions as a coenzyme for **Carboxylation reactions** (adding $CO_2$), such as Pyruvate carboxylase and Acetyl-CoA carboxylase. *Note: Biotin adds $CO_2$, while Thiamine helps remove it.* **High-Yield Clinical Pearls for NEET-PG:** * **Wernicke-Korsakoff Syndrome:** Classic triad of ataxia, ophthalmoplegia, and confusion due to thiamine deficiency, often seen in chronic alcoholics. * **Maple Syrup Urine Disease (MSUD):** Caused by a deficiency in the branched-chain α-keto acid dehydrogenase complex; some variants are "Thiamine-responsive." * **Transketolase:** An enzyme in the HMP shunt that requires TPP; measuring its activity in RBCs is the gold standard for diagnosing thiamine deficiency.

Q: What is intrinsic factor related to?

Cobalamin absorption. **Explanation:** **Intrinsic Factor (IF)** is a glycoprotein secreted by the **parietal cells** of the gastric fundus and body. It is essential for the absorption of **Vitamin B12 (Cobalamin)**. 1. **Mechanism of Absorption:** Dietary B12 is released from proteins by gastric acid and binds to R-binders (haptocorrin). In the duodenum, pancreatic proteases digest R-binders, allowing B12 to bind to Intrinsic Factor. This **B12-IF complex** travels to the **terminal ileum**, where it binds to specific receptors (Cubilin) for absorption into the portal circulation. **Analysis of Incorrect Options:** * **Vitamin D:** Absorption is dependent on bile salts and micelle formation in the proximal small intestine, as it is a fat-soluble vitamin. * **Folate absorption:** Occurs primarily in the **jejunum** via the Proton-Coupled Folate Transporter (PCFT). It does not require Intrinsic Factor. * **Vitamin C:** This is a water-soluble vitamin absorbed in the distal small intestine via sodium-dependent active transport (SVCT1 and 2). **Clinical Pearls for NEET-PG:** * **Pernicious Anemia:** An autoimmune destruction of parietal cells leading to IF deficiency, resulting in megaloblastic anemia and neurological symptoms (Subacute Combined Degeneration of the spinal cord). * **Schilling Test:** Historically used to differentiate between causes of B12 deficiency (e.g., IF deficiency vs. ileal pathology). * **Site of Absorption:** Remember the mnemonic **"Iron in the Duodenum, Folate in the Jejunum, and B12 in the Ileum."**

Q: Excessive intake of which of the following vitamins is associated with an increased risk of congenital malformations?

Vitamin-A. **Explanation:** **Vitamin A (Retinol)** is the correct answer because it is a known **teratogen** when consumed in excessive amounts during pregnancy. High doses of preformed Vitamin A (Retinoids) interfere with the normal signaling of **Hox genes** and neural crest cell migration during embryogenesis. This can lead to **Retinoic Acid Embryopathy**, characterized by craniofacial abnormalities (cleft palate, microtia), cardiac defects (transposition of great vessels), and central nervous system malformations. Due to this risk, the use of Isotretinoin (a Vitamin A derivative for acne) is strictly contraindicated in pregnancy. **Why other options are incorrect:** * **Biotin (Vitamin B7):** It is a water-soluble coenzyme for carboxylase enzymes. There is no documented evidence linking high intake to congenital malformations in humans. * **Folic Acid (Vitamin B9):** Unlike Vitamin A, folic acid supplementation is actually **protective** against malformations. It is routinely prescribed periconceptionally to prevent Neural Tube Defects (NTDs). * **Vitamin K:** Essential for the gamma-carboxylation of clotting factors (II, VII, IX, X). While Vitamin K deficiency can cause hemorrhagic disease of the newborn, its excess is not associated with teratogenicity. **High-Yield Clinical Pearls for NEET-PG:** * **Safe Limit:** Pregnant women should avoid supplements containing >10,000 IU of Vitamin A. * **Beta-carotene:** Unlike preformed Vitamin A, the precursor beta-carotene (found in carrots) is **not** teratogenic. * **Isotretinoin Rule:** Female patients must use two forms of contraception and have a negative pregnancy test before starting Isotretinoin (IPLEDGE program). * **Vitamin A Toxicity:** Chronic toxicity in adults presents as pseudotumor cerebri (idiopathic intracranial hypertension), hepatomegaly, and bone pain.

Q: The conversion of propionyl CoA to succinyl CoA requires which of the following vitamins/coenzymes?

Biotin and Vitamin B12. ### Explanation The conversion of **Propionyl CoA to Succinyl CoA** is a crucial metabolic pathway for the oxidation of odd-chain fatty acids and certain amino acids (Valine, Isoleucine, Methionine, and Threonine). This pathway occurs in three steps, two of which require specific vitamin cofactors: 1. **Propionyl CoA → Methylmalonyl CoA:** Catalyzed by *Propionyl CoA carboxylase*. Like most carboxylation reactions, this requires **Biotin (Vitamin B7)**, ATP, and CO₂. 2. **L-Methylmalonyl CoA → Succinyl CoA:** Catalyzed by *Methylmalonyl CoA mutase*. This isomerization requires **Adenosylcobalamin (Vitamin B12)**. **Why other options are incorrect:** * **Thiamine pyrophosphate (TPP):** Required for oxidative decarboxylation (e.g., Pyruvate dehydrogenase, α-ketoglutarate dehydrogenase). * **FAD and NAD+:** These are redox cofactors used in the Electron Transport Chain and Beta-oxidation of even-chain fatty acids, but they are not the primary cofactors for this specific conversion. * **Coenzyme A:** While Propionyl CoA contains CoA, it is not the "required vitamin/coenzyme" driving the conversion steps. **Clinical Pearls for NEET-PG:** * **Methylmalonic Aciduria:** A deficiency in Vitamin B12 or the mutase enzyme leads to an accumulation of methylmalonic acid, causing metabolic acidosis and neurological damage. * **Odd-chain Fatty Acids:** These are the only lipids that are **glucogenic** because Succinyl CoA can enter the TCA cycle and eventually form glucose via gluconeogenesis. * **VOMIT mnemonic:** The precursors for this pathway are **V**aline, **O**dd-chain FAs, **M**ethionine, **I**soleucine, and **T**hreonine.

Question 1

Which of the following is NOT seen in vitamin A deficiency?

Accepted Answer

Polyneuritis

Answer

Night blindness

Answer

Follicular hyperkeratosis

Answer

Growth retardation

Question 2

Bald tongue is seen in deficiency of which vitamin?

Accepted Answer

Niacin

Answer

Riboflavin

Answer

Vitamin B12

Answer

None of the above

Question 3

Which of the following combinations of biologically active molecules does vitamin A consist of?

Accepted Answer

Retinol, retinal, and retinoic acid

Answer

Retinol, retinal, and tetrahydrofolate

Answer

Retinol, iconjugase, and retinoic acid

Answer

PABA, retinal, and retinaldehyde

Question 4

Pyridoxine is essential for the generation of which coenzyme?

Accepted Answer

NAD (Nicotinamide Adenine Dinucleotide)

Answer

FAD (Flavin Adenine Dinucleotide)

Answer

ATP (Adenosine Triphosphate)

Answer

None of the above

Question 5

Which vitamin is essential for both bone formation and the coagulation cascade?

Accepted Answer

Vitamin K

Answer

Vitamin A

Answer

Vitamin D

Answer

Vitamin E

Question 6

Which test is used to diagnose thiamine deficiency?

Accepted Answer

RBC transketolase

Answer

FIGLU excretion

Answer

Methyl-malonic acid in urine

Answer

Histidine load test

Question 7

Decarboxylation reactions require which of the following vitamins as a coenzyme?

Accepted Answer

Thiamine

Answer

Riboflavin

Answer

Niacin

Answer

Biotin

Question 8

What is intrinsic factor related to?

Accepted Answer

Cobalamin absorption

Answer

Vitamin D

Answer

Folate absorption

Answer

Vitamin C

Question 9

Excessive intake of which of the following vitamins is associated with an increased risk of congenital malformations?

Accepted Answer

Vitamin-A

Answer

Biotin

Answer

Folic acid

Answer

Vitamin-K

Question 10

The conversion of propionyl CoA to succinyl CoA requires which of the following vitamins/coenzymes?

Accepted Answer

Biotin and Vitamin B12

Answer

Thiamine pyrophosphate

Answer

FAD and NAD+

Answer

Coenzyme A

Vitamins and Coenzymes — MCQs

Vitamins and Coenzymes — MCQs

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