Vitamins and Coenzymes Practice Questions

Q: Which vitamin is required for glutathione to act as an antioxidant?

Niacin. **Explanation:** The correct answer is **Niacin (Vitamin B3)**. To understand why, we must look at the **Glutathione Redox Cycle**, which is the cell's primary defense against oxidative stress (Reactive Oxygen Species). **Why Niacin is Correct:** Glutathione exists in two forms: reduced (GSH) and oxidized (GSSG). To neutralize hydrogen peroxide, GSH is converted to GSSG by *Glutathione Peroxidase*. To remain effective, GSSG must be recycled back to GSH by the enzyme **Glutathione Reductase**. This enzyme requires **NADPH** as a mandatory co-factor to donate electrons. Niacin is the precursor for **NADP+/NADPH**. Without Niacin, NADPH levels drop, the recycling of glutathione fails, and the cell suffers oxidative damage. **Why Other Options are Incorrect:** * **Vitamin E:** While a potent antioxidant that protects lipid membranes, it does not serve as a co-factor for the enzymatic regeneration of glutathione. * **Vitamin C:** It works synergistically with Vitamin E and can help regenerate it, but it is not the direct co-enzyme required for the Glutathione Reductase reaction. * **Vitamin A:** Primarily involved in vision (retinal) and gene expression (retinoic acid); it does not play a direct role in the glutathione redox cycle. **Clinical Pearls for NEET-PG:** * **The HMP Shunt Connection:** The NADPH required for this process is primarily generated by the **Pentose Phosphate Pathway (HMP Shunt)** via the enzyme **G6PD**. * **G6PD Deficiency:** In G6PD deficiency, NADPH is low, leading to decreased reduced glutathione. This results in hemoglobin denaturation (forming **Heinz bodies**) and subsequent hemolysis. * **Selenium Connection:** While Niacin is the vitamin required, **Selenium** is the essential trace element required as a co-factor for *Glutathione Peroxidase*.

Q: All of the following are seen in vitamin C deficiency except?

Infertility. **Explanation:** Vitamin C (Ascorbic acid) is a water-soluble vitamin essential for the hydroxylation of proline and lysine residues during **collagen synthesis**. Deficiency leads to **Scurvy**, a condition characterized by weakened connective tissues and capillary fragility. * **Why Infertility is the correct answer:** Infertility is not a classic clinical feature of Vitamin C deficiency. While antioxidants play a role in reproductive health, infertility is primarily associated with deficiencies in **Vitamin E** (often called the "anti-sterility vitamin") or hormonal imbalances, rather than Vitamin C. * **Why other options are incorrect:** * **Swollen, bleeding gums:** Collagen is vital for the integrity of the periodontal ligament and capillary walls. Deficiency leads to "spongy" gums that bleed easily upon touch. * **Delayed wound healing:** Collagen is the primary structural protein required for tissue repair. Without adequate Vitamin C, the formation of new connective tissue is impaired, leading to poor wound healing or dehiscence of old scars. * **Anemia:** Vitamin C deficiency causes anemia through two mechanisms: (1) Chronic blood loss from mucosal surfaces, and (2) Vitamin C is essential for the **absorption of non-heme iron** by reducing it from the ferric ($Fe^{3+}$) to the ferrous ($Fe^{2+}$) state. **High-Yield Clinical Pearls for NEET-PG:** * **Earliest sign of Scurvy:** Follicular hyperkeratosis. * **Characteristic Hemorrhages:** Perifollicular hemorrhages and "Corkscrew hairs." * **Infantile Scurvy (Barlow’s Disease):** Presents with subperiosteal hemorrhage causing "pseudoparalysis" and a "Frog-like position" of legs. * **Radiological signs:** White line of Fraenkel, Wimberger’s ring sign, and Pelkan spur.

Q: What is one of the earliest symptoms of Vitamin A deficiency?

Nyctalopia. **Explanation:** **1. Why Nyctalopia is Correct:** Nyctalopia, or **night blindness**, is the earliest clinical manifestation of Vitamin A deficiency. Vitamin A (Retinol) is essential for the synthesis of **Rhodopsin** (visual purple) in the rod cells of the retina. Rhodopsin is responsible for vision in dim light. When Vitamin A levels drop, the regeneration of rhodopsin is impaired, leading to a decreased ability to see in low light. This is often the first symptom reported by the patient. **2. Why Other Options are Incorrect:** * **Xerophthalmia:** This is a spectrum of eye diseases caused by Vitamin A deficiency. While Nyctalopia is the first stage, Xerophthalmia refers to the progression into pathological dryness of the conjunctiva and cornea. * **Bitot’s Spots:** These are triangular, foamy, silvery-white patches on the bulbar conjunctiva. They represent keratinization of the conjunctiva and occur *after* night blindness has already manifested. * **Keratomalacia:** This is the **most severe** and late-stage manifestation. It involves liquefaction and necrosis of the cornea, leading to permanent blindness. **3. NEET-PG High-Yield Pearls:** * **WHO Classification of Xerophthalmia:** * **X1A:** Conjunctival xerosis * **X1B:** Bitot’s spots * **X2:** Corneal xerosis * **X3A/X3B:** Corneal ulceration/Keratomalacia * **Earliest Sign:** Conjunctival xerosis (objective sign). * **Earliest Symptom:** Nyctalopia (subjective complaint). * **Wald’s Visual Cycle:** Retinol is converted to 11-cis-retinal, which combines with opsin to form Rhodopsin. * **Treatment:** The standard WHO schedule for children >1 year is 200,000 IU of Vitamin A orally on days 0, 1, and 14.

Q: What is the active moiety of Coenzyme A?

Thiol group of pantetheine. **Explanation:** **1. Why the Correct Answer is Right:** Coenzyme A (CoA-SH) is a vital cofactor derived from Vitamin B5 (Pantothenic acid). Its primary function is to act as a carrier of acyl groups (like acetyl or succinyl) in metabolism. The "business end" or **active moiety** of the molecule is the **thiol (-SH) group**. This thiol group is specifically located at the end of the **cysteamine** residue, which, when combined with pantothenic acid, forms **pantetheine**. Acyl groups bind to this thiol group via a high-energy **thioester bond**, allowing them to be activated for various biochemical reactions like the TCA cycle and fatty acid synthesis. **2. Why the Incorrect Options are Wrong:** * **Option A (Acetyl group):** This is a substrate that binds to CoA to form Acetyl-CoA; it is not a structural part of the coenzyme itself. * **Option B (Pantothenic acid):** While Vitamin B5 is a structural precursor of CoA, it does not contain the reactive thiol group required for acyl group attachment. * **Option C (Thiol group of beta-alanine):** Beta-alanine is a component of pantothenic acid, but it does not possess a thiol group. The thiol group is provided by the amino acid **cysteine** (as cysteamine). **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Components of CoA:** Adenosine 3',5'-bisphosphate + Pantothenic acid + Cysteamine. * **Rate-limiting step of CoA synthesis:** Phosphorylation of pantothenate by *pantothenate kinase*. * **High-energy bond:** The thioester bond in Acetyl-CoA is more energy-rich than an oxygen-ester bond, facilitating group transfer. * **Acyl Carrier Protein (ACP):** In fatty acid synthesis, the active moiety is also the 4'-phosphopantetheine group, similar to CoA.

Q: Subacute combined degeneration of the spinal cord is a feature of which vitamin deficiency?

Vitamin B12. **Explanation:** **Subacute Combined Degeneration (SCD)** of the spinal cord is a classic neurological manifestation of **Vitamin B12 (Cobalamin) deficiency**. **Why Vitamin B12 is the correct answer:** Vitamin B12 is a cofactor for the enzyme **Methylmalonyl-CoA mutase**, which converts methylmalonyl-CoA to succinyl-CoA. In B12 deficiency, methylmalonic acid (MMA) accumulates. This leads to the synthesis of abnormal fatty acids that are incorporated into neuronal lipids, causing **demyelination**. SCD specifically affects the **Posterior columns** (loss of vibration and position sense) and the **Lateral corticospinal tracts** (spastic paresis), hence the term "combined" degeneration. **Why the other options are incorrect:** * **Vitamin A:** Deficiency primarily leads to ocular symptoms like night blindness (nyctalopia) and xerophthalmia, not spinal cord degeneration. * **Vitamin B6 (Pyridoxine):** Deficiency typically causes peripheral neuropathy, sideroblastic anemia, and seizures, but does not cause SCD. * **Vitamin B9 (Folate):** While folate deficiency causes megaloblastic anemia identical to B12 deficiency, it **does not** cause neurological symptoms. Treating B12 deficiency with folate alone can worsen the neurological damage. **High-Yield Clinical Pearls for NEET-PG:** * **Schilling Test:** Historically used to diagnose the cause of B12 malabsorption. * **Pernicious Anemia:** The most common cause of B12 deficiency due to lack of Intrinsic Factor. * **Biochemical Markers:** In B12 deficiency, both **Homocysteine** and **Methylmalonic acid (MMA)** levels are elevated. In Folate deficiency, only Homocysteine is elevated. * **Peripheral Smear:** Look for hypersegmented neutrophils and macro-ovalocytes.

Q: Nyctalopia is due to deficiency of?

Vitamin A. **Explanation:** **Correct Answer: A. Vitamin A** Nyctalopia (night blindness) is the earliest clinical manifestation of Vitamin A deficiency. Vitamin A (Retinol) is essential for the synthesis of **Rhodopsin** (visual purple), a light-sensitive pigment found in the rod cells of the retina. Rods are responsible for vision in dim light. When light strikes the retina, Rhodopsin dissociates into opsin and all-trans-retinal (the Wald’s Visual Cycle). A deficiency in Vitamin A leads to an inability to regenerate Rhodopsin, resulting in impaired dark adaptation and night blindness. **Why other options are incorrect:** * **Vitamin B:** Deficiency typically leads to Beriberi (B1), Cheilosis/Glossitis (B2), Pellagra (B3), or Megaloblastic anemia (B12), but does not directly cause night blindness. * **Vitamin C:** Deficiency leads to **Scurvy**, characterized by defective collagen synthesis, bleeding gums, and impaired wound healing. * **Vitamin E:** Acts primarily as an antioxidant. Deficiency leads to hemolytic anemia and neurological symptoms (posterior column signs), but not nyctalopia. **NEET-PG High-Yield Pearls:** * **Sequence of Ocular Signs (WHO):** X1A (Conjunctival xerosis) → X1B (**Bitot’s spots**) → X2 (Corneal xerosis) → X3A/X3B (**Keratomalacia** - liquefaction of the cornea). * **Bitot’s Spots:** Triangular, foamy, pearly-white patches on the bulbar conjunctiva due to squamous metaplasia. * **Golden Rice:** A genetically modified variety of rice rich in Beta-carotene, developed to combat Vitamin A deficiency. * **Storage:** Vitamin A is stored in the **Ito cells** (Stellate cells) of the liver.

Q: Conjunctival xerosis is caused by which vitamin deficiency?

Vitamin A. ***Vitamin A***- Vitamin A is crucial for the maintenance and differentiation of **epithelial cells**, including those of the conjunctiva.- Deficiency leads to **xerophthalmia**, starting with **night blindness** and progressing to **conjunctival xerosis** (dryness) and eventual **keratomalacia**.*Vitamin K*- Vitamin K is essential for the hepatic synthesis of **clotting factors** (II, VII, IX, X).- Deficiency results in a **coagulopathy** characterized by **excessive bleeding** and prolonged prothrombin time (PT).*Vitamin C*- Vitamin C (*ascorbic acid*) is vital for the hydroxylation of **proline and lysine** during **collagen synthesis**.- Deficiency causes **Scurvy**, symptomatically involving **fragile capillaries**, **gingival swelling and bleeding**, and impaired wound healing.*Vitamin D*- Vitamin D's primary role is regulating **calcium and phosphate metabolism** to maintain bone health.- Deficiency leads to **Rickets** in children and **Osteomalacia** in adults, primarily affecting the skeletal system.

Q: Which of the following deficiencies causes follicular hyperkeratosis?

Vitamin A. ***Vitamin A***- Deficiency in Vitamin A (retinol) impairs the differentiation of **keratinizing epithelia**, leading to **squamous metaplasia**.- This results in **follicular hyperkeratosis** (also known as **phrynoderma** or 'toad skin'), where keratin plugs block the hair follicles, giving the skin a rough, bumpy appearance.*Vitamin C*- Deficiency causes **scurvy**, primarily due to defective collagen synthesis, leading to fragile blood vessels.- The characteristic skin finding is **perifollicular hemorrhage** (petechiae around hair follicles) and **painless gum bleeding**, not hyperkeratosis due to keratin plugging.*Vitamin E*- This deficiency primarily acts as an **antioxidant deficiency**, leading to increased susceptibility of cell membranes to oxidative damage.- Clinical manifestations often include **hemolytic anemia** (due to erythrocyte membrane damage) and **neurological symptoms** (e.g., ataxia, peripheral neuropathy).*Vitamin B6*- Deficiency of pyridoxine is often associated with cutaneous symptoms like a **seborrheic dermatitis-like rash** and **cheilosis** (cracked lips).- It is crucial for coenzyme functions but does not directly cause the severe keratin plugging characterized by widespread follicular hyperkeratosis.

Question 1

Which vitamin is required for glutathione to act as an antioxidant?

Accepted Answer

Niacin

Answer

Vitamin E

Answer

Vitamin C

Answer

Vitamin A

Question 2

A 50-year-old woman presents with easy fatigability, a smooth sore tongue, numbness and tingling of the feet, and weakness of the legs. A complete blood count shows a megaloblastic anemia that is not reversed by folate therapy. Hemoglobin is 5.6 g/dL, WBC count is 5,100/mL, and platelets are 240,000/mL. This patient most likely has a deficiency of which of the following vitamins?

Accepted Answer

Vitamin B12

Answer

Vitamin B1 (thiamine)

Answer

Vitamin B2 (riboflavin)

Answer

Vitamin K

Question 3

Which form of vitamin D is measured in serum?

Accepted Answer

24,25-dihydroxyvitamin D

Answer

Cholecalciferol

Answer

25-hydroxyvitamin D

Answer

1,25-dihydroxyvitamin D

Question 4

All of the following are seen in vitamin C deficiency except?

Accepted Answer

Infertility

Answer

Swollen, bleeding gums

Answer

Delayed wound healing

Answer

Anemia

Question 5

What is one of the earliest symptoms of Vitamin A deficiency?

Accepted Answer

Nyctalopia

Answer

Xerophthalmia

Answer

Bitot's spot

Answer

Keratomalacia

Question 6

What is the active moiety of Coenzyme A?

Accepted Answer

Thiol group of pantetheine

Answer

Acetyl group

Answer

Pantothenic acid

Answer

Thiol group of beta-alanine

Question 7

Subacute combined degeneration of the spinal cord is a feature of which vitamin deficiency?

Accepted Answer

Vitamin B12

Answer

Vitamin A

Answer

Vitamin B6

Answer

Vitamin B9

Question 8

Nyctalopia is due to deficiency of?

Accepted Answer

Vitamin A

Answer

Vitamin B

Answer

Vitamin C

Answer

Vitamin E

Question 9

Conjunctival xerosis is caused by which vitamin deficiency?

Accepted Answer

Vitamin A

Answer

Vitamin K

Answer

Vitamin C

Answer

Vitamin D

Question 10

Which of the following deficiencies causes follicular hyperkeratosis?

Accepted Answer

Vitamin A

Answer

Vitamin C

Answer

Vitamin E

Answer

Vitamin B6

Vitamins and Coenzymes — MCQs

Vitamins and Coenzymes — MCQs

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