Vitamins and Coenzymes Practice Questions

Q: Activity of glutathione reductase in RBCs gives an idea about the functional index of which of the following vitamins?

Riboflavin. **Explanation:** The correct answer is **Riboflavin (Vitamin B2)**. The functional status of vitamins is often assessed by measuring the activity of specific enzymes that require them as cofactors. Riboflavin is the precursor for **Flavin Adenine Dinucleotide (FAD)** and **Flavin Mononucleotide (FMN)**. **Glutathione Reductase (GR)** is an FAD-dependent enzyme found in Red Blood Cells (RBCs) that maintains the pool of reduced glutathione, which is essential for protecting cells against oxidative stress. In clinical practice, the **Erythrocyte Glutathione Reductase Activation Coefficient (EGRAC)** test is used; if the enzyme activity increases significantly upon adding FAD *in vitro*, it indicates a functional deficiency of Riboflavin in the patient. **Why other options are incorrect:** * **Pyridoxine (B6):** Its functional status is measured via **Erythrocyte Transaminase** activity (AST/ALT). * **Niacin (B3):** While Niacin provides NADPH (a co-substrate for GR), it is not the prosthetic group of the enzyme. Niacin status is typically assessed by measuring urinary metabolites (N-methylnicotinamide). * **Biotin (B7):** Biotin acts as a coenzyme for carboxylation reactions (e.g., Pyruvate carboxylase). It is not involved in the glutathione redox cycle. **High-Yield Clinical Pearls for NEET-PG:** * **Thiamine (B1):** Functional index is measured by **Erythrocyte Transketolase** activity. * **Riboflavin Deficiency:** Characterized by the "3 Cs"—**C**heilosis, **C**orneal vascularization, and **C**asual (Magenta) tongue. * **Glutathione Reductase** requires **NADPH** (from the HMP shunt) as a reducing equivalent and **FAD** (from B2) as a prosthetic group.

Q: A 5-year-old female patient complains of deformed legs and is a strict vegetarian. Lab investigations reveal elevated alkaline phosphatase. Which vitamin deficiency is most likely causing these symptoms, and what is its recommended dietary allowance?

400 IU. ### Explanation **Clinical Correlation:** The patient presents with **Rickets**, characterized by skeletal deformities ("deformed legs") and elevated **Alkaline Phosphatase (ALP)**. In children, Vitamin D deficiency leads to impaired mineralization of the osteoid matrix. Elevated ALP is a hallmark biochemical marker indicating increased osteoblastic activity attempting to compensate for the weak bone structure. Strict vegetarians are at higher risk if they lack adequate sunlight exposure, as Vitamin D is primarily found in animal products (D3) or synthesized via UV rays. **Why Option B is Correct:** According to the Indian Council of Medical Research (ICMR) and international guidelines (like the AAP), the **Recommended Dietary Allowance (RDA) for Vitamin D** in infants and children (up to 18 years) is **400 IU/day**. This dose is sufficient to maintain serum 25(OH)D levels above 20 ng/mL, preventing rickets and supporting calcium absorption. **Why Other Options are Incorrect:** * **Option A (300 IU):** This is below the established threshold for preventing nutritional rickets in the pediatric population. * **Option C (500 IU):** While safe, this is not the standard RDA defined by major health organizations for this age group. * **Option D (600 IU):** This is the RDA for adults (19–70 years) and pregnant/lactating women according to some guidelines (e.g., US IOM), but 400 IU remains the specific target for pediatric prevention. **High-Yield Clinical Pearls for NEET-PG:** * **Active Form:** 1,25-dihydroxycholicalciferol (Calcitriol). * **Storage Form:** 25-hydroxyvitamin D (Calcidiol) – measured to assess status. * **Biochemical Triad of Rickets:** Low/Normal Calcium, Low Phosphate, and **High Alkaline Phosphatase**. * **Radiological Sign:** Cupping, splaying, and fraying of metaphyses (best seen at the wrist). * **Vegetarian Source:** Vitamin D2 (Ergocalciferol) from fungi/yeast; Vitamin D3 (Cholecalciferol) is animal-derived.

Q: Which of the following vitamin deficiencies is associated with hyperplasia and keratinization of salivary glands?

Vitamin A. **Explanation:** **Vitamin A (Retinol)** is essential for maintaining the integrity and differentiation of epithelial tissues throughout the body. It acts as a regulator of gene expression by binding to nuclear receptors (RAR/RXR). In the absence of Vitamin A, specialized epithelia (like the columnar epithelium of the salivary glands, respiratory tract, and urinary tract) undergo **squamous metaplasia**. This leads to **hyperplasia** of the basal cells and excessive production of keratin (**keratinization**), causing the glands to become plugged and lose their secretory function. This same process in the eye leads to Xerophthalmia. **Why other options are incorrect:** * **Vitamin B:** Deficiencies typically manifest as neurological symptoms (B1, B12), dermatitis/glossitis (B2, B3, B6), or megaloblastic anemia (B9, B12), but do not cause generalized squamous metaplasia of glandular tissue. * **Vitamin C:** Deficiency (Scurvy) leads to defective collagen synthesis, resulting in gingival bleeding, perifollicular hemorrhages, and poor wound healing, rather than keratinization. * **Vitamin K:** This is essential for the gamma-carboxylation of clotting factors (II, VII, IX, X). Deficiency leads to bleeding diathesis and increased PT/INR. **High-Yield Clinical Pearls for NEET-PG:** * **Bitot’s Spots:** Triangular, pearly-white foamy patches on the conjunctiva due to squamous metaplasia (pathognomonic for Vitamin A deficiency). * **Follicular Hyperkeratosis:** Also known as "Phrynoderma" or toad skin; seen in severe Vitamin A deficiency. * **All-trans retinoic acid (ATRA):** Used in the treatment of Acute Promyelocytic Leukemia (M3). * **Teratogenicity:** Isotretinoin (used for acne) is highly teratogenic; a negative pregnancy test is mandatory before prescription.

Q: Vitamin A deficiency causes all of the following EXCEPT?

Loss of weight, irritability, loss of hair and joint pains. **Explanation** The correct answer is **D (Loss of weight, irritability, loss of hair, and joint pains)** because these symptoms are characteristic of **Hypervitaminosis A (Vitamin A Toxicity)**, not deficiency. In NEET-PG, it is crucial to distinguish between the clinical features of deficiency and toxicity. **Why Option D is the correct answer (Toxicity):** Chronic ingestion of excessive Vitamin A (usually >10 times the RDA) leads to toxicity. Key features include: * **Skin/Hair:** Alopecia (loss of hair) and dry, scaly skin. * **Skeletal:** Bone pain and joint pains due to cortical thickening of long bones. * **Neurological:** Irritability and increased intracranial pressure (Pseudotumor cerebri). **Why other options are incorrect (Deficiency features):** * **Option A (Growth retardation):** Vitamin A (Retinoic acid) acts like a hormone, regulating gene expression for osteoblast and osteoclast activity. Deficiency leads to impaired skeletal remodeling and stunted growth. * **Option B (Sterility):** Retinol is essential for maintaining the health of the germinal epithelium. Its absence leads to the degeneration of seminiferous tubules and failure of spermatogenesis. * **Option C (Nyctalopia):** This is the earliest symptom of Vitamin A deficiency. It occurs due to the failure to regenerate **Rhodopsin** (visual purple) in the rod cells of the retina, leading to night blindness. **High-Yield Clinical Pearls for NEET-PG:** * **Earliest Symptom:** Nyctalopia (Night blindness). * **Earliest Sign:** Conjunctival Xerosis. * **Pathognomonic Sign:** Bitot’s spots (triangular, foamy patches on the conjunctiva). * **Keratomalacia:** Liquefactive necrosis of the cornea; a medical emergency. * **Teratogenicity:** Isotretinoin (Vitamin A analogue) is highly teratogenic; a negative pregnancy test is mandatory before prescription.

Q: Seborrheic dermatitis is produced by deficiency of which vitamin?

Vitamin B2. ### Explanation **Correct Option: C (Vitamin B2 / Riboflavin)** The correct answer is **Vitamin B2 (Riboflavin)**. Riboflavin deficiency, often referred to as **Ariboflavinosis**, classically presents with a "seborrheic dermatitis-like" eruption. The underlying medical concept involves the role of riboflavin as a precursor to FAD and FMN, cofactors essential for lipid metabolism and skin integrity. Deficiency leads to inflammation of the sebaceous-rich areas, resulting in greasy, scaly plaques on the nasolabial folds, scrotum, and scalp. **Analysis of Incorrect Options:** * **Vitamin C (Ascorbic Acid):** Deficiency causes **Scurvy**. Clinical features include perifollicular hemorrhages, corkscrew hairs, and bleeding gums, rather than seborrheic-pattern dermatitis. * **Vitamin B1 (Thiamine):** Deficiency leads to **Beriberi** (Dry/Wet) or Wernicke-Korsakoff syndrome. It primarily affects the cardiovascular and nervous systems, not the skin. * **Vitamin A (Retinol):** Deficiency typically causes **Phrynoderma** (follicular hyperkeratosis) and ocular symptoms like xerophthalmia and Bitot’s spots. **Clinical Pearls for NEET-PG:** 1. **The "2-O" Rule for B2:** Riboflavin deficiency is characterized by **O**ro-oculo-genital syndrome (Cheilosis, Angular stomatitis, Glossitis, and Seborrheic dermatitis of the scrotum/face). 2. **Vitamin B6 (Pyridoxine) Connection:** B6 deficiency can also present with a seborrheic-like rash; however, in standard medical examinations, B2 is the classic association for this specific question. 3. **Etiology Note:** While vitamin deficiencies cause "seborrheic-like" rashes, the most common cause of Seborrheic Dermatitis in the general population is an inflammatory response to the yeast ***Malassezia furfur***. 4. **Zinc Deficiency:** Do not confuse this with **Acrodermatitis Enteropathica**, which presents with periorificial and acral dermatitis.

Q: Which of the following is a non-vitamin coenzyme?

Lipoic acid. **Explanation:** The correct answer is **Lipoic acid** (Option C). **Understanding the Concept:** Coenzymes are non-protein organic molecules required by enzymes for catalytic activity. Most coenzymes are derivatives of water-soluble B-complex vitamins. However, **non-vitamin coenzymes** are substances that function as coenzymes but can be synthesized de novo by the human body in sufficient quantities, meaning they do not meet the strict dietary definition of a "vitamin." **Lipoic acid** (Thioctic acid) is a sulfur-containing fatty acid that acts as a coenzyme for oxidative decarboxylation reactions (e.g., Pyruvate Dehydrogenase and α-Ketoglutarate Dehydrogenase complexes). Since the body can synthesize it from octanoic acid and cysteine, it is classified as a non-vitamin coenzyme. **Analysis of Other Options:** * **A. Niacin:** This is Vitamin B3. It is the precursor for the coenzymes **NAD+ and NADP+**. * **B. Coenzyme A:** This is the active coenzyme form of **Pantothenic acid** (Vitamin B5). * **D. SAM (S-Adenosylmethionine):** While SAM is also a non-vitamin coenzyme (derived from ATP and Methionine), **Lipoic acid** is the more classic textbook example cited in NEET-PG for this category, specifically regarding its role in multi-enzyme complexes. *Note: In some contexts, SAM is considered a co-substrate/methyl donor.* **Clinical Pearls for NEET-PG:** 1. **The "Big Five":** Oxidative decarboxylation of α-keto acids requires five cofactors: **T**hiamine (B1), **R**iboflavin (B2), **N**iacin (B3), **P**antothenic acid (B5), and **L**ipoic acid (Mnemonic: **T**ender **R**omance **N**ever **P**recedes **L**ove). 2. **Arsenic Poisoning:** Arsenite inhibits enzymes by binding to the -SH groups of **Lipoic acid**, leading to lactic acidosis and neurological symptoms. 3. Other non-vitamin coenzymes include **ATP, Coenzyme Q (Ubiquinone), and Heme.**

Q: Vitamin K is used in which step of clotting factor activation?

Carboxylation. ### Explanation **Correct Answer: B. Carboxylation** Vitamin K acts as an 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)** on clotting factors **II, VII, IX, and X**, as well as proteins C and S. The addition of a carboxyl group ($CO_2$) gives these proteins a negative charge, allowing them to bind to positively charged **Calcium ions ($Ca^{2+}$)**. This calcium bridge enables the clotting factors to anchor onto the phospholipid surfaces of activated platelets, a critical step in the coagulation cascade. During this reaction, Vitamin K is oxidized to an epoxide form and must be recycled back to its active hydroquinone form by the enzyme **Vitamin K Epoxide Reductase (VKOR)**. **Why other options are incorrect:** * **A. Methylation:** This process involves the addition of a methyl group (e.g., conversion of homocysteine to methionine), typically requiring Vitamin B12 and Folate. * **C. Hydroxylation:** This is characteristic of **Vitamin C**, which is a cofactor for prolyl and lysyl hydroxylase in collagen synthesis. * **D. Transketolation:** This is a part of the Hexose Monophosphate (HMP) shunt, requiring **Thiamine (Vitamin B1)** as a cofactor. **High-Yield Clinical Pearls for NEET-PG:** * **Warfarin Mechanism:** Inhibits VKOR, preventing the recycling of Vitamin K and thus inhibiting the carboxylation of factors II, VII, IX, and X. * **Newborns:** They are Vitamin K deficient due to sterile guts and poor placental transfer; hence, a prophylactic Vitamin K injection is given at birth to prevent **Hemorrhagic Disease of the Newborn**. * **Lab Marker:** Vitamin K deficiency or Warfarin use is primarily monitored using **Prothrombin Time (PT/INR)**.

Q: Which of the following is NOT true about Vitamin C?

It reduces ferrous iron to ferric iron.. **Explanation:** **1. Why Option D is the Correct Answer (The Incorrect Statement):** Vitamin C (Ascorbic acid) is a powerful reducing agent. In the process of iron absorption, it **reduces ferric iron ($Fe^{3+}$)**—which is the insoluble form found in food—to **ferrous iron ($Fe^{2+}$)**. The ferrous form is the only form that can be absorbed by the intestinal mucosal cells via the divalent metal transporter 1 (DMT1). Therefore, the statement that it reduces ferrous to ferric is chemically reversed and incorrect. **2. Analysis of Other Options:** * **Option A:** Vitamin C is a classic **water-soluble** vitamin. Unlike fat-soluble vitamins, it is not stored in significant amounts in the body (except in the adrenal glands) and is excreted in the urine. * **Option B:** It is the **most heat-labile** vitamin. Cooking, boiling, or even prolonged storage of vegetables significantly reduces their Vitamin C content due to oxidation. * **Option C:** It acts as a **potent antioxidant** by scavenging free radicals and regenerating Vitamin E (tocopherol) from its oxidized form, protecting membranes from lipid peroxidation. **3. High-Yield Clinical Pearls for NEET-PG:** * **Collagen Synthesis:** Vitamin C is a co-factor for **prolyl and lysyl hydroxylase**, essential for the post-translational modification of collagen. Deficiency leads to **Scurvy** (corkscrew hair, bleeding gums, impaired wound healing). * **Bile Acid Synthesis:** It is required for the **7-alpha-hydroxylase** step (rate-limiting step) in converting cholesterol to bile acids. * **Catecholamine Synthesis:** It is a cofactor for **Dopamine $\beta$-hydroxylase**, which converts Dopamine to Norepinephrine. * **Hyperoxaluria:** Excessive intake of Vitamin C can lead to increased oxalate excretion, potentially causing **calcium oxalate kidney stones**.

Q: A patient presents with serum calcium of 7.8 mg/dL, high 25-hydroxyvitamin D levels, and low 1-alpha-hydroxylase levels. Which of the following is the most appropriate treatment for this condition?

Calcitriol. ### Explanation The patient presents with **hypocalcemia** (7.8 mg/dL) despite having high levels of 25-hydroxyvitamin D [25(OH)D]. The critical finding is the **low level of 1-alpha-hydroxylase**, the enzyme responsible for converting 25(OH)D (calcifediol) into its active form, 1,25-dihydroxyvitamin D (calcitriol). **Why Calcitriol is correct:** In the presence of 1-alpha-hydroxylase deficiency (commonly seen in Chronic Kidney Disease or Vitamin D-Dependent Rickets Type 1), the body cannot activate vitamin D. Therefore, administering precursors like D3 or calcifediol is ineffective. **Calcitriol** is the active form of Vitamin D and bypasses the need for renal 1-alpha-hydroxylation, directly increasing intestinal calcium absorption and normalizing serum calcium. **Why other options are incorrect:** * **Phosphate supplementation:** This would further lower serum calcium by forming calcium-phosphate complexes and is contraindicated in hypocalcemia. * **Calcifediol [25(OH)D]:** This is the substrate for 1-alpha-hydroxylase. Since the enzyme is deficient, providing more substrate will not lead to the production of the active hormone. * **Vitamin D3 (Cholecalciferol):** This requires two hydroxylation steps (liver then kidney). It is ineffective if the final renal activation step is impaired. **NEET-PG High-Yield Pearls:** * **Rate-limiting step:** The conversion of 25(OH)D to 1,25(OH)₂D by 1-alpha-hydroxylase in the proximal convoluted tubule is the most strictly regulated step in Vitamin D metabolism. * **Stimulators of 1-alpha-hydroxylase:** Low serum Calcium, low serum Phosphate, and high PTH. * **Inhibitor:** High Calcitriol (feedback inhibition) and FGF-23. * **Storage form:** 25-hydroxyvitamin D (Calcifediol) is the major circulating form used to clinically assess a patient's Vitamin D status.

Question 1

The Schilling test is used to diagnose which condition?

Accepted Answer

Vitamin B12 deficiency

Answer

Folic acid deficiency

Answer

Vitamin B6 deficiency

Answer

Vitamin D deficiency

Question 2

Activity of glutathione reductase in RBCs gives an idea about the functional index of which of the following vitamins?

Accepted Answer

Riboflavin

Answer

Pyridoxine

Answer

Niacin

Answer

Biotin

Question 3

A 5-year-old female patient complains of deformed legs and is a strict vegetarian. Lab investigations reveal elevated alkaline phosphatase. Which vitamin deficiency is most likely causing these symptoms, and what is its recommended dietary allowance?

Accepted Answer

400 IU

Answer

300 IU

Answer

500 IU

Answer

600 IU

Question 4

Which of the following vitamin deficiencies is associated with hyperplasia and keratinization of salivary glands?

Accepted Answer

Vitamin A

Answer

Vitamin B

Answer

Vitamin C

Answer

Vitamin K

Question 5

Vitamin A deficiency causes all of the following EXCEPT?

Accepted Answer

Loss of weight, irritability, loss of hair and joint pains

Answer

Growth retardation due to impairment in skeletal formation

Answer

Degeneration of germinal epithelium leading to sterility in males

Answer

Nyctalopia

Question 6

Seborrheic dermatitis is produced by deficiency of which vitamin?

Accepted Answer

Vitamin B2

Answer

Vitamin C

Answer

Vitamin B1

Answer

Vitamin A

Question 7

Which of the following is a non-vitamin coenzyme?

Accepted Answer

Lipoic acid

Answer

Niacin

Answer

Coenzyme A

Answer

SAM

Question 8

Vitamin K is used in which step of clotting factor activation?

Accepted Answer

Carboxylation

Answer

Methylation

Answer

Hydroxylation

Answer

Transketolation

Question 9

Which of the following is NOT true about Vitamin C?

Accepted Answer

It reduces ferrous iron to ferric iron.

Answer

It is a water-soluble vitamin.

Answer

It is most sensitive to heat.

Answer

It is a potent antioxidant.

Question 10

A patient presents with serum calcium of 7.8 mg/dL, high 25-hydroxyvitamin D levels, and low 1-alpha-hydroxylase levels. Which of the following is the most appropriate treatment for this condition?

Accepted Answer

Calcitriol

Answer

Phosphate supplementation

Answer

Calcifediol

Answer

Vitamin D3

Vitamins and Coenzymes — MCQs

Vitamins and Coenzymes — MCQs

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