Vitamins and Coenzymes Practice Questions

Q: Which of the following enzymes require Vitamin C for their activity?

Procollagen proline hydroxylase. **Explanation:** **1. Why Option A is Correct:** Vitamin C (Ascorbic acid) acts as a vital reducing agent in the post-translational modification of collagen. The enzymes **Prolyl hydroxylase** (Procollagen proline hydroxylase) and **Lysyl hydroxylase** require Vitamin C to maintain the iron cofactor in its reduced **ferrous (Fe²⁺) state**. This hydroxylation of proline and lysine residues is essential for the interchain hydrogen bonding that stabilizes the collagen triple helix. Without Vitamin C, collagen fibers are weak and unstable, leading to the clinical manifestation of Scurvy. **2. Why Other Options are Incorrect:** * **Options B & C (Procollagen amino/carboxyl peptidases):** These enzymes are responsible for cleaving the N-terminal and C-terminal propeptides of procollagen in the extracellular space to form tropocollagen. They do not require Vitamin C for their catalytic activity. * **Option D (Lysyl oxidase):** While this enzyme is critical for collagen cross-linking, it is a **Copper-dependent** enzyme, not Vitamin C-dependent. It oxidatively deaminates lysine and hydroxylysine residues to form reactive aldehydes (allysine). **3. NEET-PG High-Yield Pearls:** * **Vitamin C Functions:** Beyond collagen synthesis, it is required for **Dopamine β-hydroxylase** (Dopamine → Norepinephrine) and **7-α-hydroxylase** (Bile acid synthesis). * **Scurvy Symptoms:** Remember the "4 Hs": Hemorrhage (petechiae, bleeding gums), Hyperkeratosis, Hypochondriasis, and Hematologic abnormalities (anemia). * **Iron Absorption:** Vitamin C enhances the absorption of non-heme iron by reducing it from the ferric (Fe³⁺) to the ferrous (Fe²⁺) state in the stomach.

Q: All of the following are sources of vitamin A except?

Sunflower seeds. **Explanation:** Vitamin A is found in two primary forms: **Retinoids** (preformed Vitamin A) found in animal sources and **Carotenoids** (provitamin A) found in plant sources. **Why Sunflower Seeds is the Correct Answer:** Sunflower seeds are a rich source of **Vitamin E (Tocopherol)** and healthy fats, but they contain negligible amounts of Vitamin A. In the context of NEET-PG, it is crucial to remember that most seeds and vegetable oils (except Red Palm Oil) are characterized by their Vitamin E content rather than Vitamin A. **Analysis of Incorrect Options:** * **Egg:** An excellent source of preformed Vitamin A (retinol), specifically concentrated in the **egg yolk**. * **Milk:** Whole milk and dairy products are significant animal sources of retinol. In many regions, milk is also fortified with Vitamin A. * **Tomato:** Contains **Lycopene** and **Beta-carotene**. Beta-carotene is a provitamin carotenoid that the body converts into retinal, making tomatoes a valid plant source. **NEET-PG High-Yield Pearls:** 1. **Richest Source:** The richest natural source of Vitamin A is **Halibut liver oil**, followed by Cod liver oil. 2. **Plant Sources:** The richest plant source is **Red Palm Oil** (contains high concentrations of alpha and beta-carotenes). 3. **Storage:** Vitamin A is stored in the liver in **Ito cells** (Stellate cells) as retinyl palmitate. 4. **Golden Rice:** A genetically modified variety of rice produced to biosynthesize beta-carotene to prevent Vitamin A deficiency in developing nations.

Q: What is the triad of biotin deficiency?

Dermatitis, glossitis, Alopecia. **Explanation:** Biotin (Vitamin B7) acts as a vital coenzyme for **carboxylation reactions**, including those catalyzed by pyruvate carboxylase, acetyl-CoA carboxylase, and propionyl-CoA carboxylase. These reactions are essential for gluconeogenesis, fatty acid synthesis, and amino acid metabolism. **1. Why Option B is Correct:** The classic clinical triad of biotin deficiency consists of **Dermatitis** (typically periorificial, scaly, and erythematous), **Glossitis** (inflammation of the tongue), and **Alopecia** (hair loss). These symptoms arise because biotin is crucial for the synthesis of fatty acids and the maintenance of rapidly dividing cells in the skin and hair follicles. **2. Analysis of Incorrect Options:** * **Option A:** While dermatitis and glossitis occur, **Steatorrhea** (fatty stools) is not a feature of biotin deficiency; it is more commonly associated with malabsorption syndromes or Vitamin E/K deficiencies. * **Option C:** Mental changes (lethargy, hallucinations) can occur in severe biotin deficiency, but **Diarrhoea** is not a primary component of the triad. * **Option D:** This describes the **"3 Ds" of Pellagra** (Niacin/Vitamin B3 deficiency): Dermatitis, Dementia, and Diarrhoea. **High-Yield NEET-PG Pearls:** * **Avidin Connection:** Consumption of large amounts of **raw egg whites** can induce biotin deficiency because the protein avidin binds biotin with high affinity, preventing its absorption. * **Key Enzymes:** Remember the mnemonic **"ABC"** for carboxylases—they require **A**TP, **B**iotin, and **C**O₂. * **Metabolic Marker:** Deficiency leads to the accumulation of odd-chain fatty acids and organic aciduria (e.g., 3-hydroxyisovaleric acid).

Q: Beri-beri is caused by a deficiency of which vitamin?

Thiamine. **Explanation:** **Beri-beri** is the clinical manifestation of **Thiamine (Vitamin B1)** deficiency. Thiamine acts as a crucial co-enzyme (Thiamine Pyrophosphate - TPP) in carbohydrate metabolism, specifically in the decarboxylation of pyruvic acid. When deficient, pyruvic acid accumulates in the blood, leading to neurological and cardiovascular impairment. * **Dry Beri-beri:** Characterized by peripheral neuropathy (wrist drop/foot drop) and muscle wasting. * **Wet Beri-beri:** Characterized by high-output cardiac failure and edema. * **Wernicke-Korsakoff Syndrome:** An acute/chronic brain syndrome often seen in alcoholics due to thiamine deficiency. **Why other options are incorrect:** * **Folic Acid (B9):** Deficiency leads to **Megaloblastic anemia** and Neural Tube Defects (NTDs) in fetuses. * **Riboflavin (B2):** Deficiency causes **Ariboflavinosis**, characterized by angular stomatitis, cheilosis, and glossitis (magenta tongue). * **Niacin (B3):** Deficiency leads to **Pellagra**, classically identified by the "4 Ds": Dermatitis (Casal’s necklace), Diarrhea, Dementia, and Death. **High-Yield Clinical Pearls for NEET-PG:** * **Infantile Beri-beri:** Occurs in infants (2–4 months) breastfed by thiamine-deficient mothers; presents with "aphonic cry" and cardiac failure. * **Milling of Rice:** Polishing rice removes the pericarp (outer layer) which is rich in Thiamine, making polished rice eaters highly susceptible to Beri-beri. * **Staple Diet:** Beri-beri is historically associated with populations consuming **polished/white rice**, while Pellagra is associated with **Maize/Jowar** diets.

Q: A 40-year-old man presents with megaloblastic anemia and early neurological abnormalities. Which drug is most likely required?

Vitamin B12. The clinical presentation of **megaloblastic anemia** combined with **neurological abnormalities** is the classic hallmark of **Vitamin B12 (Cobalamin) deficiency**. **Why Vitamin B12 is correct:** Vitamin B12 is essential for two critical enzymatic reactions: 1. **DNA Synthesis:** It acts as a cofactor for methionine synthase, which converts homocysteine to methionine [1]. This process recycles folate; without B12, folate is "trapped" (the **Folate Trap**), leading to impaired DNA synthesis and megaloblastic changes [1]. 2. **Myelin Integrity:** B12 is a cofactor for methylmalonyl-CoA mutase. Deficiency leads to an accumulation of **methylmalonic acid (MMA)**, which results in the synthesis of abnormal fatty acids that incorporate into neuronal lipids. This causes **Subacute Combined Degeneration (SCD)** of the spinal cord, manifesting as paresthesia, loss of vibration/proprioception, and ataxia [2]. **Why other options are incorrect:** * **Folic acid:** While it can correct the megaloblastic anemia (by bypassing the folate trap), it **cannot** correct the neurological deficits [3]. In fact, giving folic acid alone in B12 deficiency can worsen neurological damage. * **Iron sulfate:** Used for microcytic hypochromic anemia, not megaloblastic anemia. * **Erythropoietin:** Used for anemia of chronic kidney disease; it does not address vitamin deficiencies. **High-Yield NEET-PG Pearls:** * **Diagnostic Marker:** Elevated levels of **Methylmalonic Acid (MMA)** are specific for B12 deficiency, whereas **Homocysteine** is elevated in both B12 and Folate deficiency [1]. * **Schilling Test:** Historically used to determine the cause of B12 malabsorption (e.g., Pernicious Anemia). * **Neurological involvement:** Always rule out B12 deficiency before starting Folate to prevent irreversible cord damage [2].

Q: A patient presents with severe energy deficiency. Which of the following vitamins might be deficient in this patient?

Thiamin. **Explanation:** **Thiamin (Vitamin B1)** is the correct answer because its active form, **Thiamin Pyrophosphate (TPP)**, is a critical coenzyme for key enzymes in carbohydrate metabolism and energy production. Specifically, it is required by: 1. **Pyruvate Dehydrogenase (PDH):** Converts Pyruvate to Acetyl-CoA (linking glycolysis to the TCA cycle). 2. **$\alpha$-Ketoglutarate Dehydrogenase:** A rate-limiting step in the TCA cycle. 3. **Branched-chain $\alpha$-ketoacid Dehydrogenase:** Essential for metabolizing leucine, isoleucine, and valine. A deficiency in Thiamin leads to a "metabolic logjam," preventing the efficient oxidation of glucose and resulting in a severe ATP (energy) deficit, clinically manifesting as **Beriberi** or **Wernicke-Korsakoff syndrome**. **Analysis of Incorrect Options:** * **Pyridoxine (B6):** Primarily involved in amino acid metabolism (transamination and decarboxylation) and heme synthesis. While important, its deficiency does not present primarily as a generalized energy crisis. * **Riboflavin (B2):** Precursor for FAD and FMN. While involved in the electron transport chain, Thiamin deficiency is more classically associated with acute energy failure and lactic acidosis in clinical vignettes. * **Folic Acid (B9):** Essential for one-carbon metabolism and DNA synthesis. Deficiency leads to megaloblastic anemia, not acute energy deficiency. **NEET-PG High-Yield Pearls:** * **The "Dehydrogenase" Rule:** TPP is a coenzyme for most oxidative decarboxylation reactions. * **Clinical Marker:** Erythrocyte **Transketolase** activity is the most reliable diagnostic test for Thiamin deficiency. * **Wernicke’s Encephalopathy Triad:** Confusion, Ataxia, and Ophthalmoplegia. * **Management Tip:** Always administer Thiamin *before* Glucose in a malnourished patient to prevent precipitating Wernicke’s encephalopathy.

Q: Perifollicular and petechial hemorrhages are characteristic of which condition?

Scurvy. **Explanation:** **Correct Answer: C. Scurvy** Scurvy is caused by a deficiency of **Vitamin C (Ascorbic acid)**. Vitamin C is a crucial co-factor for the enzymes **prolyl hydroxylase** and **lysyl hydroxylase**, which are responsible for the hydroxylation of proline and lysine residues during collagen synthesis. In its absence, defective collagen (lacking cross-linking) leads to increased capillary fragility. * **Perifollicular hemorrhages** (bleeding around hair follicles) and **petechiae** (small red/purple spots) are hallmark signs of this vascular fragility. Other classic features include "corkscrew hairs," swollen spongy gums, and impaired wound healing. **Incorrect Options:** * **A. Acrodermatitis enteropathica:** This is an autosomal recessive disorder of **Zinc absorption**. It presents with a triad of periorificial/acral dermatitis, alopecia, and diarrhea, rather than hemorrhagic spots. * **B. Pellagra:** Caused by **Niacin (Vitamin B3)** deficiency. It is characterized by the "4 Ds": Dermatitis (Casal’s necklace), Diarrhea, Dementia, and Death. The dermatitis is typically photosensitive and symmetrical. * **D. Phrynoderma:** Also known as "toad skin," this is follicular hyperkeratosis associated with **Vitamin A** deficiency (and sometimes Essential Fatty Acids). It presents as dry, firm papules on the extensor surfaces, not hemorrhages. **NEET-PG High-Yield Pearls:** * **Vitamin C and Iron:** Vitamin C enhances the absorption of non-heme iron by keeping it in the ferrous ($Fe^{2+}$) state. * **Infantile Scurvy (Barlow’s Disease):** Look for "ground glass appearance" of bones and "Frankel’s line" (white line of calcification) on X-ray. * **Collagen Type:** Scurvy primarily affects the stability of the triple helix in **Type I and Type III collagen**.

Question 1

Which vitamin deficiency in alcoholics inhibits pyruvate dehydrogenase?

Accepted Answer

Thiamin

Answer

Niacin

Answer

Riboflavin

Answer

Ascorbic acid

Question 2

A patient presents with pellagra, parkinsonism, convulsions, anemia, and kidney stones. This presentation is most indicative of a deficiency in which of the following?

Accepted Answer

Pyridoxal phosphate

Answer

Coenzyme A

Answer

FADH

Answer

Niacin

Question 3

Which of the following enzymes require Vitamin C for their activity?

Accepted Answer

Procollagen proline hydroxylase

Answer

Procollagen amino peptidase

Answer

Procollagen carboxyl peptidase

Answer

Lysyl oxidase

Question 4

Which is the most potent chain-breaking antioxidant?

Accepted Answer

Alpha-tocopherol

Answer

Vitamin C

Answer

Catalase

Answer

Glutathione peroxidase

Question 5

All of the following are sources of vitamin A except?

Accepted Answer

Sunflower seeds

Answer

Egg

Answer

Milk

Answer

Tomato

Question 6

What is the triad of biotin deficiency?

Accepted Answer

Dermatitis, glossitis, Alopecia

Answer

Dermatitis, glossitis, Steatorrhea

Answer

Mental changes, diarrhoea, Alopecia

Answer

Dermatitis, dementia, diarrhoea

Question 7

Beri-beri is caused by a deficiency of which vitamin?

Accepted Answer

Thiamine

Answer

Folic acid

Answer

Riboflavin

Answer

Niacin

Question 8

A 40-year-old man presents with megaloblastic anemia and early neurological abnormalities. Which drug is most likely required?

Accepted Answer

Vitamin B12

Answer

Folic acid

Answer

Iron sulfate

Answer

Erythropoietin

Question 9

A patient presents with severe energy deficiency. Which of the following vitamins might be deficient in this patient?

Accepted Answer

Thiamin

Answer

Pyridoxine

Answer

Riboflavin

Answer

Folic acid

Question 10

Perifollicular and petechial hemorrhages are characteristic of which condition?

Accepted Answer

Scurvy

Answer

Acrodermatitis enteropathica

Answer

Pellagra

Answer

Phrynoderma

Vitamins and Coenzymes — MCQs

Vitamins and Coenzymes — MCQs

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