Vitamins and Coenzymes Practice Questions

Q: Which of the following is a serum marker of rickets?

Alkaline phosphatase. **Explanation:** In rickets (and osteomalacia), the primary biochemical hallmark is an **elevation in serum Alkaline Phosphatase (ALP)**. This occurs because rickets is characterized by a failure of osteoid mineralization. To compensate for the weakened bone structure, **osteoblastic activity** increases. Since ALP is a byproduct of osteoblast activity (reflecting bone turnover), its levels rise significantly. It is often the earliest and most sensitive biochemical marker of the disease, frequently rising before radiological changes appear. **Analysis of Incorrect Options:** * **Acid Phosphatase (ACP):** This is a marker of **osteoclast** activity and is primarily used as a marker for prostatic carcinoma or Gaucher’s disease, not metabolic bone disease like rickets. * **Decreased Serum Calcium:** While calcium can be low, it is often **normal** in early or moderate rickets due to compensatory secondary hyperparathyroidism, which mobilizes calcium from bones to maintain serum levels. Therefore, it is not as reliable a marker as ALP. * **Urinary Phosphates:** While phosphate metabolism is affected, urinary phosphate levels are variable and influenced by PTH; they are not considered a primary diagnostic "serum marker" for the condition. **NEET-PG High-Yield Pearls:** * **Earliest sign of Rickets:** Increase in serum Alkaline Phosphatase. * **Most specific radiological sign:** Cupping, splaying, and fraying of the metaphysis (best seen at the wrist). * **Biochemical Profile:** Low/Normal Calcium, Low Phosphate, **High ALP**, and High PTH (Secondary Hyperparathyroidism). * **Vitamin D-dependent Rickets Type II:** Characterized by end-organ resistance to 1,25(OH)₂D (mutated receptors) and often presents with alopecia.

Q: Scurvy is the result of deficiency of which vitamin?

Vitamin C. **Explanation:** **Vitamin C (Ascorbic Acid)** is the correct answer. It serves as a vital co-factor for the enzymes **prolyl hydroxylase** and **lysyl hydroxylase**. These enzymes are responsible for the post-translational hydroxylation of proline and lysine residues in collagen synthesis. Hydroxyproline is essential for stabilizing the collagen triple helix via hydrogen bonding. In Vitamin C deficiency, defective collagen synthesis leads to capillary fragility and poor wound healing, manifesting clinically as **Scurvy**. **Analysis of Incorrect Options:** * **Vitamin A (Retinol):** Deficiency primarily affects vision and epithelial integrity, leading to Night Blindness, Xerophthalmia, and Bitot’s spots. * **Vitamin B:** This is a complex of vitamins. Specific deficiencies lead to Beriberi (B1), Cheilosis/Glossitis (B2), Pellagra (B3), or Megaloblastic anemia (B12/B9). * **Vitamin D (Calciferol):** Deficiency leads to impaired calcium absorption, resulting in Rickets in children and Osteomalacia in adults. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Triad of Scurvy:** Perifollicular hemorrhages, Corkscrew hair, and Bleeding gums (swollen, spongy gums). * **Radiological Signs:** Look for **Wimberger’s sign** (ring epiphysis), **Frankel’s line** (white line of Scorbutus), and **Pelkan spurs**. * **Key Function:** Vitamin C also aids in **Iron absorption** (maintains iron in the ferrous $Fe^{2+}$ state) and acts as a potent antioxidant. * **Synthesis:** Humans cannot synthesize Vitamin C due to the absence of the enzyme **L-gulonolactone oxidase**.

Q: Which of the following is not a form of vitamin D?

Ergosterol. ### Explanation The correct answer is **Ergosterol** because it is a **provitamin** (a precursor) found in plants and fungi, not an active or intermediate form of Vitamin D itself. #### Why Ergosterol is the Correct Choice: Ergosterol is the plant-derived precursor that, upon exposure to ultraviolet (UV) light, is converted into **Ergocalciferol (Vitamin D2)**. While it is essential for the synthesis of Vitamin D2, the molecule itself does not possess Vitamin D activity in the human body until it undergoes photochemical conversion. #### Analysis of Other Options: * **Cholecalciferol (Vitamin D3):** This is the form of Vitamin D synthesized in the skin of animals and humans from 7-dehydrocholesterol via UV radiation. It is also found in oily fish and egg yolks. * **Calcifediol (25-hydroxyvitamin D3):** This is the major **circulating form** of Vitamin D. It is produced in the **liver** by the action of the enzyme 25-hydroxylase. It is the clinical marker used to transition/measure a patient's Vitamin D status. * **Calcitriol (1,25-dihydroxyvitamin D3):** This is the **biologically active form** of Vitamin D. It is produced in the **kidneys** via the enzyme 1-alpha-hydroxylase. It acts as a hormone to increase intestinal calcium absorption. #### NEET-PG High-Yield Pearls: 1. **Rate-limiting step:** The conversion of Calcifediol to Calcitriol in the kidney (regulated by PTH). 2. **Storage:** Vitamin D is stored primarily in **adipose tissue**, but the liver produces the main circulating form (Calcifediol). 3. **Deficiency:** Leads to **Rickets** in children (delayed osteoid mineralization) and **Osteomalacia** in adults (remodeling defect). 4. **Activation Sequence:** Skin (D3) $\rightarrow$ Liver (25-OH) $\rightarrow$ Kidney (1,25-OH₂).

Q: Neurotoxicity is seen with excess of which vitamin?

Vitamin B6. **Explanation:** The correct answer is **Vitamin B6 (Pyridoxine)**. While most water-soluble vitamins are excreted in the urine when consumed in excess, Vitamin B6 is a notable exception. Chronic ingestion of high doses (typically >200-500 mg/day) leads to **sensory neuropathy**. The mechanism involves the accumulation of pyridoxine in the dorsal root ganglia, leading to axonal degeneration. Clinically, this manifests as progressive sensory ataxia, numbness, and diminished proprioception. **Analysis of Incorrect Options:** * **Vitamin B12 (Cobalamin):** It has a very high safety profile. No known toxicity is associated with high doses; instead, its *deficiency* causes subacute combined degeneration of the spinal cord (SCD). * **Vitamin B2 (Riboflavin):** It is non-toxic even in large amounts. Excess intake simply results in "flavinuria," where the urine turns a bright fluorescent yellow. * **Vitamin C (Ascorbic Acid):** Massive doses are generally well-tolerated but can lead to gastrointestinal upset (diarrhea) or the formation of **oxalate kidney stones** due to its metabolic breakdown into oxalate. It does not cause neurotoxicity. **High-Yield Clinical Pearls for NEET-PG:** * **The B6 Paradox:** Both deficiency and toxicity of B6 can cause neuropathy. Deficiency typically presents with peripheral neuropathy and convulsions (due to decreased GABA synthesis), while toxicity presents as a pure sensory neuropathy. * **Isoniazid (INH) Connection:** INH therapy for TB induces B6 deficiency by forming pyridoxal-hydrazone complexes. Always co-prescribe B6 (10-50 mg) to prevent peripheral neuropathy. * **Sideroblastic Anemia:** B6 is a cofactor for ALA synthase; its deficiency can lead to microcytic hypochromic anemia with ringed sideroblasts.

Q: What vitamin supplementation is advised when a person is on treatment for tuberculosis?

Pyridoxine. **Explanation:** The correct answer is **Pyridoxine (Vitamin B6)**. **Why Pyridoxine is the correct answer:** The primary drug used in the treatment of tuberculosis is **Isoniazid (INH)**. Isoniazid is structurally similar to pyridoxine and interferes with its metabolism in two ways: 1. It inhibits the enzyme **pyridoxine phosphokinase**, which converts pyridoxine to its active form, **Pyridoxal-5-Phosphate (PLP)**. 2. It reacts with PLP to form an inactive hydrazone complex, which is then excreted in the urine. A deficiency of PLP leads to decreased synthesis of neurotransmitters (like GABA), resulting in **peripheral neuropathy**. Therefore, prophylactic supplementation of 10–50 mg/day of Pyridoxine is mandatory for patients on INH to prevent this neurological side effect. **Why other options are incorrect:** * **Thiamine (B1):** Deficiency causes Beriberi or Wernicke-Korsakoff syndrome, typically associated with chronic alcoholism, not anti-tubercular therapy. * **Biotin (B7):** Acts as a coenzyme for carboxylation reactions. Deficiency is rare but can be induced by excessive raw egg white consumption (avidin). * **Niacin (B3):** While INH can theoretically cause Pellagra (by inhibiting the conversion of Tryptophan to Niacin), Pyridoxine is the standard supplement specifically indicated to prevent the more common dose-related neuropathy. **High-Yield Clinical Pearls for NEET-PG:** * **Sideroblastic Anemia:** INH can also cause this because PLP is a cofactor for **ALA synthase**, the rate-limiting enzyme in heme synthesis. * **High-risk groups:** Diabetics, alcoholics, and malnourished patients are more prone to INH-induced neuropathy and must always receive B6. * **Drug-Nutrient Interaction:** Always remember the triad: **INH – B6 Deficiency – Peripheral Neuropathy.**

Q: Which of the following are coenzymes for pyruvate dehydrogenase?

NADPH. **Explanation:** The **Pyruvate Dehydrogenase (PDH) Complex** is a multi-enzyme system that converts pyruvate into Acetyl-CoA, linking glycolysis to the TCA cycle. This complex requires **five specific coenzymes**, often remembered by the mnemonic **"Tender Loving Care For Nancy."** 1. **T**hiamine pyrophosphate (TPP) – Derived from Vitamin B1 2. **L**ipoic acid (Lipoamide) 3. **C**oenzyme A (CoA) – Derived from Vitamin B5 (Pantothenic acid) 4. **F**AD – Derived from Vitamin B2 (Riboflavin) 5. **N**AD+ – Derived from Vitamin B3 (Niacin) **Why NADPH is the correct answer (the exception):** The question asks which of the following is a coenzyme for PDH. However, in the context of standard NEET-PG multiple-choice patterns, if the question asks for an "except" or identifies the outlier, **NADPH** is the correct choice because it is **not** involved in the PDH reaction. PDH uses **NAD+** (the oxidized form) as an electron acceptor to produce **NADH**. NADPH is primarily used in reductive biosynthesis (like fatty acid synthesis) and the HMP shunt, not in the oxidative decarboxylation of pyruvate. **Analysis of Incorrect Options:** * **A, B, and C:** TPP, CoA, and Lipoic acid are all essential prosthetic groups or substrates for the three subunits of the PDH complex (E1, E2, and E3 respectively). **High-Yield Clinical Pearls for NEET-PG:** * **Arsenic Poisoning:** Arsenite inhibits PDH by binding to the -SH groups of **Lipoic acid**, leading to lactic acidosis and neurological symptoms. * **Thiamine Deficiency:** Leads to Beriberi and Wernicke-Korsakoff syndrome because PDH and Alpha-ketoglutarate dehydrogenase cannot function without TPP. * **Regulation:** PDH is inhibited by its products (**Acetyl-CoA and NADH**) and activated by **Calcium** (important in skeletal muscle).

Question 1

Which of the following is a serum marker of rickets?

Accepted Answer

Alkaline phosphatase

Answer

Acid phosphatase

Answer

Decreased serum calcium

Answer

Urinary phosphates

Question 2

Scurvy is the result of deficiency of which vitamin?

Accepted Answer

Vitamin C

Answer

Vitamin A

Answer

Vitamin B

Answer

Vitamin D

Question 3

Which of the following is not a form of vitamin D?

Accepted Answer

Ergosterol

Answer

Cholecalciferol

Answer

Calcifediol

Answer

Calcitriol

Question 4

Neurotoxicity is seen with excess of which vitamin?

Accepted Answer

Vitamin B6

Answer

Vitamin B12

Answer

Vitamin B2

Answer

Vitamin C

Question 5

Which disease is NOT due to Vitamin B deficiency?

Accepted Answer

Scurvy

Answer

Acrodermatitis

Answer

Beri-Beri

Answer

Neuropathy

Question 6

What vitamin supplementation is advised when a person is on treatment for tuberculosis?

Accepted Answer

Pyridoxine

Answer

Thiamine

Answer

Biotin

Answer

Niacin

Question 7

The Histidine load test is indicated for which of the following conditions?

Accepted Answer

Folic acid deficiency

Answer

Histidine deficiency

Answer

Glutamate deficiency

Answer

Vitamin B12 deficiency

Question 8

A 55-year-old man, a chronic alcoholic, presented with confusion, ataxia, and diplopia. What is the appropriate treatment protocol?

Accepted Answer

Thiamine injection followed by glucose infusion

Answer

Thiamine infusion alone

Answer

Glucose infusion alone

Answer

Glucose infusion followed by thiamine injection

Question 9

The level of circulating 1,25-dihydroxycholecalciferol is significantly reduced in patients with chronic liver disease because:

Accepted Answer

The liver can no longer efficiently convert vitamin D to 25-hydroxycholecalciferol.

Answer

The liver can no longer efficiently convert 25-hydroxycholecalciferol to 1,25-dihydroxycholecalciferol.

Answer

The liver can no longer efficiently convert vitamin D to cholecalciferol.

Answer

The liver can no longer efficiently convert cholecalciferol to 1,25-dihydroxycholecalciferol.

Question 10

Which of the following are coenzymes for pyruvate dehydrogenase?

Accepted Answer

NADPH

Answer

Thiamine pyrophosphate (TPP)

Answer

Coenzyme A (CoA)

Answer

Lipoic acid

Vitamins and Coenzymes — MCQs

Vitamins and Coenzymes — MCQs

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