Vitamins and Coenzymes — MCQs

A 30-year-old male presented with complaints of chapping and fissuring of the lips, a sore red tongue, and oily, scaly skin rashes on the scrotum, vulva, and philtrum. Lab findings reveal increased activity of glutathione reductase in the RBCs. Which of the following enzymes use the deficient vitamin as a coenzyme?

Q458Medium

Hypervitaminosis E leads to which of the following complications?

Q459Easy

Inhibition of bile secretion will NOT reduce the intestinal absorption of which of the following?

Q460Easy

Tryptophan load test helps in the evaluation of deficiency of which vitamin?

Vitamins and Coenzymes Indian Medical PG Practice Questions and MCQs

Question 451: The '3-D's' are associated with which of the following conditions?

A. Rickets
B. Scurvy
C. Beri-Beri
D. Pellagra (Correct Answer)

Explanation: **Explanation:** The correct answer is **Pellagra (Option D)**. Pellagra is a nutritional deficiency disease caused by a lack of **Niacin (Vitamin B3)** or its precursor amino acid, **Tryptophan**. The "3-D's" refer to the classic clinical triad of Pellagra: 1. **Dermatitis:** Characteristically occurs on sun-exposed areas (photosensitivity). A well-known sign is **Casal’s necklace**, a scaly rash around the neck. 2. **Diarrhea:** Resulting from inflammation of the gastrointestinal mucosa. 3. **Dementia:** Representing neurological involvement, which can include irritability, confusion, and memory loss. *Note: If untreated, a 4th "D"—**Death**—may occur.* **Why other options are incorrect:** * **Rickets (Option A):** Caused by **Vitamin D** deficiency in children, leading to defective mineralization of bones (e.g., bow legs, rachitic rosary). * **Scurvy (Option B):** Caused by **Vitamin C** deficiency, characterized by defective collagen synthesis leading to bleeding gums, petechiae, and impaired wound healing. * **Beri-Beri (Option C):** Caused by **Thiamine (Vitamin B1)** deficiency. It presents as "Dry Beri-Beri" (polyneuritis) or "Wet Beri-Beri" (high-output heart failure). **High-Yield Clinical Pearls for NEET-PG:** * **Hartnup Disease:** An autosomal recessive disorder affecting tryptophan absorption that can lead to "Pellagra-like" symptoms. * **Carcinoid Syndrome:** Can cause Pellagra because tryptophan is diverted to overproduce Serotonin, leaving little for Niacin synthesis. * **Corn/Maize Diets:** Pellagra is common in populations where maize is the staple food, as the niacin in maize is bound (**Niacytin**) and unavailable for absorption.

Question 452: Which of the following is a poor source of Vitamin D?

A. Fat from fish
B. Whole milk (Correct Answer)
C. Cod liver oil
D. Egg

Explanation: **Explanation:** Vitamin D (Calciferol) is a fat-soluble vitamin primarily obtained from endogenous synthesis in the skin via UV light or through specific dietary sources. **Why Whole Milk is the Correct Answer:** While milk is often associated with bone health due to its calcium content, **natural cow’s milk is a poor source of Vitamin D.** It contains only negligible amounts (approx. 0.4 to 1.0 IU/100ml). In many Western countries, milk is "fortified" with Vitamin D, but in its natural state, it cannot meet the daily requirements. This is a high-yield distinction for exams: Milk is rich in Calcium and Phosphorus but deficient in Vitamin D and Iron. **Analysis of Incorrect Options:** * **Cod liver oil:** This is the **richest natural source** of Vitamin D. It is a concentrated supplement derived from fish liver. * **Fat from fish:** Fatty fish (such as salmon, mackerel, and herring) are excellent sources of Vitamin D3 (Cholecalciferol) stored in their adipose tissue. * **Egg:** The egg yolk contains a significant amount of Vitamin D. While not as potent as fish oil, it is considered a good dietary source compared to milk. **NEET-PG High-Yield Pearls:** * **Active Form:** 1,25-dihydroxycholecalciferol (Calcitriol). * **Rate-limiting enzyme:** 1-alpha-hydroxylase (located in the proximal convoluted tubule of the kidney). * **Deficiency:** Leads to **Rickets** in children (craniotabes, rachitic rosary) and **Osteomalacia** in adults (softening of bones). * **Daily Requirement:** Approximately 400–600 IU/day for adults. * **Storage:** Unlike other fat-soluble vitamins stored in the liver, Vitamin D is primarily stored in **adipose tissue**.

Question 453: Gamma carboxylation of glutamic acid in clotting factors II, VII, and protein C is dependent on which vitamin?

A. Vitamin K (Correct Answer)
B. Vitamin C
C. Vitamin A
D. Vitamin E

Explanation: **Explanation:** **Vitamin K** is the essential cofactor for the enzyme **gamma-glutamyl carboxylase**. This enzyme catalyzes the post-translational modification of specific glutamic acid residues into **gamma-carboxyglutamic acid (Gla)**. This modification is crucial because the two carboxyl groups in Gla residues allow these proteins to bind **Calcium (Ca²⁺)**, which subsequently enables them to bind to phospholipids on platelet membranes—a vital step in the coagulation cascade. The proteins dependent on this process include: * **Clotting Factors:** II (Prothrombin), VII, IX, and X. * **Anticoagulant Proteins:** Protein C and Protein S. **Why other options are incorrect:** * **Vitamin C (Ascorbic Acid):** Acts as a cofactor for prolyl and lysyl hydroxylase, essential for **collagen synthesis**, not carboxylation. * **Vitamin A (Retinol):** Primarily involved in the visual cycle (rhodopsin formation), epithelial maintenance, and gene transcription. * **Vitamin E (Tocopherol):** Functions as a potent lipid-soluble **antioxidant**, protecting cell membranes from free radical damage. **High-Yield Clinical Pearls for NEET-PG:** * **Warfarin Mechanism:** It inhibits **Vitamin K Epoxide Reductase (VKOR)**, preventing the regeneration of active Vitamin K, thereby inhibiting the synthesis of functional factors II, VII, IX, and X. * **Newborns:** They are born with sterile guts and low Vitamin K stores, putting them at risk for **Hemorrhagic Disease of the Newborn**; hence, a prophylactic Vitamin K injection is given at birth. * **Laboratory Marker:** Vitamin K deficiency or Warfarin therapy is primarily monitored using **Prothrombin Time (PT/INR)**.

Question 454: The clinical combination of dermatitis, diarrhoea, and dementia resulting from a deficiency of niacin is referred to as?

A. Beriberi
B. Marasmus
C. Pellagra (Correct Answer)
D. Rickets

Explanation: ### Explanation **Correct Answer: C. Pellagra** **1. Why Pellagra is Correct:** Pellagra is caused by a deficiency of **Niacin (Vitamin B3)** or its precursor amino acid, **Tryptophan**. Niacin is essential for the synthesis of NAD and NADP, which are vital coenzymes for redox reactions. The clinical hallmark of Pellagra is the **"3 Ds"**: * **Dermatitis:** Characterized by a symmetrical, sun-sensitive scaly rash, often forming a "Casal’s necklace" around the neck. * **Diarrhea:** Resulting from atrophy of the gastrointestinal mucosal villi. * **Dementia:** Caused by degeneration of neurons in the brain and spinal cord. If untreated, a 4th "D"—**Death**—may occur. **2. Why Other Options are Incorrect:** * **A. Beriberi:** Caused by a deficiency of **Thiamine (Vitamin B1)**. It presents as Dry Beriberi (peripheral neuropathy) or Wet Beriberi (high-output heart failure). * **B. Marasmus:** A form of severe **Protein-Energy Malnutrition (PEM)** characterized by overall calorie deficiency, leading to extensive tissue and muscle wasting ("skin and bones" appearance). * **D. Rickets:** Caused by **Vitamin D deficiency** in children, leading to impaired mineralization of bone and skeletal deformities like bow legs. **3. NEET-PG High-Yield Pearls:** * **Hartnup Disease:** An autosomal recessive disorder involving defective tryptophan transport that can lead to pellagra-like symptoms. * **Carcinoid Syndrome:** Can cause secondary niacin deficiency because tryptophan is diverted to overproduce Serotonin. * **Maize-dependent diets:** Corn contains niacin in a bound form (niacytin) and is low in tryptophan, making these populations susceptible to Pellagra. * **Corn-based diet treatment:** Treating corn with alkali (Nixtamalization) releases the bound niacin.

Question 455: Which of the following is characteristic of pellagra?

A. It is due to pyridoxine deficiency.
B. It occurs with a diet chiefly based on maize. (Correct Answer)
C. Night blindness is a presenting feature.
D. It causes high-output cardiac failure.

Explanation: **Explanation:** **Pellagra** is caused by a deficiency of **Niacin (Vitamin B3)** or its precursor amino acid, **Tryptophan**. **Why Option B is Correct:** Maize (corn) is deficient in both Tryptophan and Niacin. Furthermore, the niacin present in maize is in a bound form called **niacytin**, which is biologically unavailable for absorption in the human gut. Therefore, populations subsisting on a diet primarily composed of maize are at high risk for developing pellagra. **Analysis of Incorrect Options:** * **Option A:** Pyridoxine (B6) deficiency can lead to secondary niacin deficiency (as B6 is a cofactor for converting Tryptophan to Niacin), but "Pellagra" specifically refers to the clinical syndrome of Niacin deficiency. * **Option C:** Night blindness (Nyctalopia) is the earliest clinical sign of **Vitamin A** deficiency, not Niacin. * **Option D:** High-output cardiac failure (Wet Beriberi) is characteristic of **Thiamine (Vitamin B1)** deficiency. **High-Yield Clinical Pearls for NEET-PG:** * **The 4 D’s of Pellagra:** Dermatitis (photosensitive, "Casal’s necklace" appearance), Diarrhea, Dementia, and Death. * **Tryptophan Metabolism:** 60 mg of Tryptophan yields 1 mg of Niacin. This process requires Vitamin **B6, B2, and Iron**. * **Secondary Pellagra:** Can occur in **Hartnup disease** (impaired tryptophan absorption) or **Carcinoid syndrome** (tryptophan is diverted to serotonin synthesis). * **Niacytin:** To make niacin in maize bioavailable, it must be treated with alkali (e.g., lime water), a process known as *nixtamalization*.

Question 456: In biliary obstruction, which vitamin deficiency will be seen?

A. Vitamin B1
B. Vitamin B12
C. Vitamin C
D. Vitamin K (Correct Answer)

Explanation: ### Explanation **Correct Option: D (Vitamin K)** The underlying medical concept here is the **absorption of fat-soluble vitamins (A, D, E, and K)**. These vitamins require bile salts for emulsification and the formation of micelles to be absorbed in the small intestine. In **biliary obstruction** (obstructive jaundice), the flow of bile into the duodenum is blocked. This leads to fat malabsorption (steatorrhea) and a subsequent failure to absorb fat-soluble vitamins. Among the options, Vitamin K is the only fat-soluble vitamin. Its deficiency leads to a decrease in the synthesis of clotting factors II, VII, IX, and X, resulting in an increased Prothrombin Time (PT) and bleeding tendencies. **Why Incorrect Options are Wrong:** * **Vitamin B1 (Thiamine), Vitamin B12 (Cobalamin), and Vitamin C (Ascorbic Acid):** These are all **water-soluble vitamins**. * Water-soluble vitamins (except B12) do not require bile or micelle formation for absorption; they are generally absorbed via active transport or diffusion directly into the portal circulation. * While Vitamin B12 absorption is complex (requiring Intrinsic Factor and an intact terminal ileum), it is not dependent on bile-mediated emulsification. **High-Yield Clinical Pearls for NEET-PG:** 1. **The "PT Test":** To differentiate between obstructive jaundice and hepatocellular jaundice, Vitamin K is administered parenterally. If the PT normalizes, the cause is obstructive (malabsorption); if it doesn't, the cause is liver cell failure. 2. **Storage:** Unlike other water-soluble vitamins, **Vitamin B12** is stored in the liver for 3–5 years. 3. **Vitamin K Cycle:** It acts as a coenzyme for **gamma-glutamyl carboxylase**, which activates clotting factors. Warfarin inhibits this cycle by blocking Vitamin K epoxide reductase.

Question 457: A 30-year-old male presented with complaints of chapping and fissuring of the lips, a sore red tongue, and oily, scaly skin rashes on the scrotum, vulva, and philtrum. Lab findings reveal increased activity of glutathione reductase in the RBCs. Which of the following enzymes use the deficient vitamin as a coenzyme?

A. Alpha-ketoglutarate dehydrogenase
B. Succinate dehydrogenase
C. Xanthine dehydrogenase
D. All of the above (Correct Answer)

Explanation: ### Explanation **1. Understanding the Deficiency** The clinical presentation—**cheilosis** (fissuring of lips), **magenta tongue** (sore red tongue), and **seborrheic dermatitis** (oily, scaly rashes on the scrotum/vulva)—is classic for **Vitamin B2 (Riboflavin) deficiency**. The definitive biochemical marker for Riboflavin deficiency is the **Erythrocyte Glutathione Reductase Activity Coefficient (EGRAC)**. Glutathione reductase requires **FAD** (Flavin Adenine Dinucleotide) as a cofactor. In deficiency states, the enzyme's activity is low but increases significantly when FAD is added *in vitro*, confirming the lack of the vitamin. **2. Why "All of the Above" is Correct** Riboflavin is the precursor for two essential coenzymes: **FMN** (Flavin Mononucleotide) and **FAD**. These are required by various "Flavoproteins" involved in redox reactions: * **Alpha-ketoglutarate dehydrogenase:** A multi-enzyme complex in the TCA cycle that uses FAD (along with B1, B3, B5, and Lipoic acid). * **Succinate dehydrogenase:** Complex II of the Electron Transport Chain and a TCA cycle enzyme; it is a quintessential flavoprotein using FAD. * **Xanthine dehydrogenase/oxidase:** Involved in purine catabolism (converting hypoxanthine to uric acid); it requires FAD and Molybdenum. **3. Clinical Pearls for NEET-PG** * **The "3 S's" of B2 deficiency:** **S**tomatitis (angular), **S**crotal dermatitis, and **S**ore tongue (Magenta). * **Corneal Neovascularization:** Another high-yield sign of Riboflavin deficiency. * **Light Sensitivity:** Riboflavin is photolabile; this is why newborns undergoing phototherapy for jaundice may develop B2 deficiency. * **Coenzyme mnemonic:** FMN and FAD are derived from **F**lavin (**F**lavin = **F**irst/Second letter of the coenzymes).

Question 458: Hypervitaminosis E leads to which of the following complications?

A. Hypercalcemia
B. Raised intracranial tension
C. Increased bleeding time (Correct Answer)
D. Psychosis

Explanation: **Explanation:** Vitamin E (Tocopherol) is a potent fat-soluble antioxidant. While it is generally considered the least toxic of the fat-soluble vitamins, high doses (Hypervitaminosis E) can lead to significant clinical complications, primarily affecting the coagulation cascade. **Why "Increased bleeding time" is correct:** The primary mechanism of Vitamin E toxicity is its **antagonism of Vitamin K**. High levels of Vitamin E interfere with the Vitamin K-dependent carboxylase enzyme system, leading to decreased levels of clotting factors II, VII, IX, and X. Clinically, this manifests as an increased risk of hemorrhage, prolonged prothrombin time (PT), and increased bleeding tendencies. This effect is particularly dangerous in patients already taking oral anticoagulants like Warfarin. **Analysis of Incorrect Options:** * **A. Hypercalcemia:** This is a hallmark of **Vitamin D toxicity**, where excessive calcium absorption from the gut and bone resorption occur. * **B. Raised intracranial tension:** This (Pseudotumor cerebri) is a classic manifestation of **Vitamin A toxicity** (Hypervitaminosis A), often accompanied by headache and papilledema. * **D. Psychosis:** While Vitamin B12 deficiency can cause neuropsychiatric symptoms, psychosis is not a recognized feature of Vitamin E toxicity. **High-Yield Clinical Pearls for NEET-PG:** * **Least Toxic:** Vitamin E is the least toxic fat-soluble vitamin. * **Drug Interaction:** Always monitor PT/INR in patients taking both Vitamin E supplements and Warfarin. * **Premature Infants:** Vitamin E is used to prevent Retinopathy of Prematurity (ROP) and Intraventricular Hemorrhage, but excessive doses in neonates can increase the risk of necrotizing enterocolitis (NEC). * **Antioxidant Role:** It prevents non-enzymatic oxidation of Polyunsaturated Fatty Acids (PUFAs) in cell membranes.

Question 459: Inhibition of bile secretion will NOT reduce the intestinal absorption of which of the following?

A. Vitamin A
B. Vitamin B1 (Correct Answer)
C. Vitamin K
D. Vitamin D

Explanation: **Explanation:** The absorption of vitamins in the human intestine depends primarily on their solubility. Vitamins are classified into two categories: **Fat-soluble (A, D, E, and K)** and **Water-soluble (B-complex and C).** **Why Vitamin B1 is Correct:** Vitamin B1 (Thiamine) is a **water-soluble vitamin**. Unlike fat-soluble vitamins, water-soluble vitamins do not require bile salts or micelle formation for absorption. They are absorbed directly into the portal blood via active transport or passive diffusion. Therefore, an inhibition of bile secretion (as seen in obstructive jaundice or cholestasis) will not affect the absorption of Vitamin B1. **Why the Other Options are Incorrect:** * **Vitamins A, D, and K:** These are all **fat-soluble vitamins**. Their absorption is strictly dependent on the presence of bile salts and pancreatic lipases. Bile salts emulsify dietary fats and form **mixed micelles**, which ferry these hydrophobic vitamins to the intestinal brush border for absorption. If bile secretion is inhibited, these vitamins cannot be absorbed, leading to deficiency states and steatorrhea. **High-Yield Clinical Pearls for NEET-PG:** * **Vitamin B12 Exception:** While most water-soluble vitamins are absorbed easily, Vitamin B12 is the exception; it requires **Intrinsic Factor (IF)** from gastric parietal cells and is absorbed in the **terminal ileum**. * **Bile Acid Sequestrants:** Drugs like Cholestyramine can lead to deficiencies of fat-soluble vitamins (A, D, E, K) by interfering with bile acid recycling. * **Vitamin K Deficiency:** This is often the first fat-soluble vitamin deficiency to manifest clinically (as an increased PT/INR) in cases of biliary obstruction because the body has limited stores compared to Vitamin A or D.

Question 460: Tryptophan load test helps in the evaluation of deficiency of which vitamin?

A. Folic acid
B. Niacinamide (Correct Answer)
C. Pyridoxine
D. Cyanocobolamine

Explanation: **Explanation:** The **Tryptophan Load Test** is used to evaluate the deficiency of **Vitamin B6 (Pyridoxine)**. However, in the context of this specific question, it evaluates the body's ability to synthesize **Niacin (B3)** from Tryptophan. **The Underlying Concept:** Tryptophan is an essential amino acid that serves as a precursor for Niacin synthesis via the **Kynurenine pathway**. A critical step in this pathway involves the enzyme **Kynureninase**, which requires **Pyridoxal Phosphate (PLP/Vitamin B6)** as a cofactor. * In the absence of B6, Tryptophan cannot be converted to Niacin. * Instead, the pathway is diverted, leading to the accumulation of **Xanthurenic acid**, which is then excreted in the urine. * Therefore, a "load" of Tryptophan results in high urinary Xanthurenic acid if there is a functional deficiency in the B6-dependent conversion to Niacin. **Analysis of Options:** * **B. Niacinamide (Correct):** The test specifically measures the metabolic failure to produce Niacin from its precursor. * **A. Folic Acid:** Evaluated by the **FIGLU (Formiminoglutamic acid) excretion test**. * **C. Pyridoxine:** While B6 is the cofactor required, the test is classically described in textbooks to assess the Tryptophan-Niacin pathway. (Note: If both B3 and B6 are options, B6 is often the more "biochemically" accurate answer, but B3 is frequently the "intended" answer in specific exam patterns regarding the end-product). * **D. Cyanocobalamin (B12):** Evaluated by the **Schilling test** or measuring **Methylmalonic acid (MMA)** levels. **High-Yield Clinical Pearls for NEET-PG:** 1. **60 mg of Tryptophan** yields **1 mg of Niacin**. 2. **Hartnup Disease:** A genetic defect in neutral amino acid (Tryptophan) transporters, leading to Pellagra-like symptoms. 3. **Carcinoid Syndrome:** Can lead to Niacin deficiency because Tryptophan is diverted to overproduce Serotonin.

Practice by Chapter

Fat-Soluble Vitamins: A, D, E, K

Practice Questions

Vitamin A and Vision

Practice Questions

Vitamin D and Calcium Metabolism

Practice Questions

Vitamin E and Antioxidant Functions

Practice Questions

Vitamin K and Blood Coagulation

Practice Questions

Water-Soluble Vitamins: B Complex and C

Practice Questions

Thiamine (B1) and Pyruvate Dehydrogenase

Practice Questions

Riboflavin (B2) and Flavin Coenzymes

Practice Questions

Niacin and NAD/NADP

Practice Questions

Vitamin B6 and Transamination

Practice Questions

Folate and Vitamin B12 in One-Carbon Metabolism

Practice Questions

Vitamin C and Collagen Synthesis

Practice Questions

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