Vitamins and Coenzymes Practice Questions

Q: Which of the following is NOT seen in vitamin A deficiency?

Polyneuritis. **Explanation:** The correct answer is **D. Polyneuritis**. **Why Polyneuritis is the correct choice:** Polyneuritis (inflammation of multiple peripheral nerves) is a classic manifestation of **Vitamin B1 (Thiamine) deficiency**, specifically seen in Dry Beriberi. Vitamin A (Retinol) is primarily involved in vision, epithelial integrity, and immune function; it does not play a direct role in peripheral nerve maintenance. Therefore, polyneuritis is not a feature of Vitamin A deficiency. **Analysis of incorrect options:** * **A. Night Blindness (Nyctalopia):** This is the earliest symptom of Vitamin A deficiency. Retinol is essential for the synthesis of **rhodopsin** (visual purple) in the rod cells of the retina, which are responsible for vision in dim light. * **B. Follicular Hyperkeratosis:** Vitamin A is vital for maintaining epithelial tissues. Deficiency leads to keratinization of the skin, resulting in a rough, "gooseflesh" appearance known as **Phrynoderma** (toad skin). * **C. Growth Retardation:** Vitamin A is essential for skeletal growth and cell differentiation. It acts like a hormone (via Retinoic Acid receptors) to regulate gene expression necessary for bone remodeling and protein synthesis. **High-Yield Clinical Pearls for NEET-PG:** * **WHO Classification of Xerophthalmia:** X1A (Conjunctival xerosis), X1B (**Bitot’s spots** - triangular pearly white foamy spots), X2 (Corneal xerosis), X3A/B (Keratomalacia/Corneal liquefaction). * **Earliest Sign:** Conjunctival xerosis. * **Earliest Symptom:** Night blindness. * **Hypervitaminosis A:** Can cause pseudotumor cerebri (increased intracranial pressure) and is highly teratogenic (avoid in pregnancy).

Q: Generalised edema can be produced by deficiency of which vitamin?

Thiamine. **Explanation:** The correct answer is **Thiamine (Vitamin B1)**. Thiamine deficiency leads to a clinical condition known as **Beriberi**, which is categorized into two main types: Dry and Wet Beriberi. **Why Thiamine is correct:** **Wet Beriberi** is characterized by cardiovascular involvement. Thiamine pyrophosphate (TPP) is a crucial cofactor for enzymes like pyruvate dehydrogenase. Its deficiency leads to impaired energy metabolism in the myocardium and peripheral vasodilation. This results in **high-output heart failure**, increased capillary hydrostatic pressure, and sodium/water retention, ultimately manifesting as **generalized edema** (anasarca) and breathlessness. **Why the other options are incorrect:** * **Vitamin A:** Deficiency primarily affects ocular health (Xerophthalmia, Night blindness) and epithelial integrity, but does not cause edema. * **Vitamin D:** Deficiency leads to Rickets (in children) and Osteomalacia (in adults) due to impaired calcium and phosphate homeostasis, affecting bone mineralization rather than fluid balance. * **Folic acid:** Deficiency results in Megaloblastic anemia and neural tube defects. While severe anemia can theoretically lead to heart failure, it is not the classic presentation for generalized edema compared to Thiamine. **NEET-PG High-Yield Pearls:** * **Dry Beriberi:** Presents as peripheral neuropathy (symmetrical muscle wasting and sensory loss) without edema. * **Wernicke-Korsakoff Syndrome:** A neuropsychiatric complication of thiamine deficiency, often seen in alcoholics, characterized by the triad of Ataxia, Ophthalmoplegia, and Confusion. * **Infantile Beriberi:** Occurs in infants breastfed by thiamine-deficient mothers; can present with sudden heart failure or aphonic cry. * **Key Enzyme:** Thiamine is a cofactor for **Alpha-ketoglutarate dehydrogenase** and **Transketolase** (measured for diagnosis).

Q: Which of the following is NOT classified under energy-releasing B-complex vitamins?

Vitamin B12 (Cobalamin). The B-complex vitamins are traditionally classified into three functional categories: **Energy-releasing**, **Hematopoietic**, and **Other**. ### 1. Why Vitamin B12 is the Correct Answer **Vitamin B12 (Cobalamin)** is primarily classified as a **Hematopoietic vitamin**. Its main roles include the maturation of erythrocytes and DNA synthesis (via the conversion of homocysteine to methionine). While it is essential for metabolism, it does not act as a direct coenzyme in the primary energy-generating pathways (like the TCA cycle or Electron Transport Chain) that oxidize carbohydrates and fats for ATP production. ### 2. Analysis of Incorrect Options (Energy-Releasing Vitamins) * **Vitamin B1 (Thiamine):** As Thiamine Pyrophosphate (TPP), it is a crucial coenzyme for **Pyruvate Dehydrogenase** and **alpha-ketoglutarate dehydrogenase**, linking glycolysis to the TCA cycle. * **Vitamin B2 (Riboflavin):** It forms **FAD and FMN**, which act as electron carriers in the TCA cycle and the respiratory chain (Complex I and II). * **Vitamin B6 (Pyridoxine):** While often associated with amino acid metabolism (transamination), it is also a required cofactor for **Glycogen Phosphorylase**, making it essential for mobilizing glucose from glycogen for energy. ### 3. NEET-PG High-Yield Pearls * **Classification Summary:** * **Energy-releasing:** B1, B2, B3 (Niacin), Biotin, and Pantothenic acid. * **Hematopoietic:** B12 and Folic acid. * **Other:** B6 (Pyridoxine) – often sits in both camps but is primarily categorized under "Other/Amino acid metabolism." * **Clinical Correlation:** Deficiency of energy-releasing B-vitamins typically manifests in high-metabolic-demand tissues, leading to **Beriberi (B1)** or **Pellagra (B3)**. * **B12 Unique Fact:** It is the only B-vitamin stored in significant amounts in the liver (3–5 years' worth).

Q: Bald tongue is seen in deficiency of which vitamin?

Niacin. **Explanation:** **Bald tongue** (atrophic glossitis) is a clinical condition characterized by the loss of filiform papillae, making the tongue appear smooth, red, and "bald." **Why Niacin (Vitamin B3) is the correct answer:** Niacin deficiency leads to **Pellagra**, classically characterized by the **4 Ds**: Dermatitis, Diarrhea, Dementia, and Death. A hallmark oral manifestation of Pellagra is a bright red, swollen, and "bald" tongue (glossitis). This occurs because Niacin (as NAD/NADP) is essential for rapid cell turnover; its deficiency impairs the regeneration of the lingual epithelium, leading to papillary atrophy. **Analysis of Incorrect Options:** * **Riboflavin (B2):** Deficiency typically presents with **Magenta tongue** (purplish-red hue), angular stomatitis, and cheilosis. While glossitis occurs, the "bald" description is more classic for Niacin or B12. * **Vitamin B12:** Deficiency causes **Hunter’s glossitis** or Moeller’s glossitis. While the tongue appears smooth and red (bald), in the context of standard NEET-PG patterns, Niacin is the primary association for the specific term "Bald tongue" related to Pellagra, whereas B12 is often linked to "Beefy red tongue." **High-Yield Clinical Pearls for NEET-PG:** * **Casal’s Necklace:** Hyperpigmented rash around the neck seen in Niacin deficiency. * **Hartnup Disease:** An autosomal recessive disorder involving impaired tryptophan transport, leading to secondary Niacin deficiency and Pellagra-like symptoms. * **Tryptophan Connection:** 60 mg of dietary Tryptophan is required to synthesize 1 mg of Niacin. * **Carcinoid Syndrome:** Can lead to Niacin deficiency because tryptophan is diverted to produce excessive Serotonin.

Q: Which of the following combinations of biologically active molecules does vitamin A consist of?

Retinol, retinal, and retinoic acid. **Explanation:** Vitamin A (Retinoids) refers to a group of biologically active polyisoprenoid compounds. The correct answer is **Option A** because Vitamin A exists in three primary active forms in the body, often referred to as the "retinoid family": 1. **Retinol:** The alcohol form, primarily used for storage (as retinyl esters) and transport. 2. **Retinal (Retinaldehyde):** The aldehyde form, essential for the visual cycle (specifically 11-cis retinal). 3. **Retinoic Acid:** The acid form, which acts as a hormone to regulate gene expression, epithelial cell differentiation, and growth. **Analysis of Incorrect Options:** * **Option B:** Includes **Tetrahydrofolate (THF)**, which is the active coenzyme form of Vitamin B9 (Folic acid), not Vitamin A. * **Option C:** Mentions **Conjugase**, which is an enzyme involved in the intestinal absorption of Folate (polyglutamate to monoglutamate conversion), not a component of Vitamin A. * **Option D:** Includes **PABA (Para-aminobenzoic acid)**, which is a structural component of Folic acid. It also lists "retinal" and "retinaldehyde" twice, as they are synonyms. **High-Yield NEET-PG Pearls:** * **Visual Cycle (Wald’s Cycle):** 11-cis retinal combines with opsin to form rhodopsin. Light causes isomerization to all-trans retinal. * **Storage:** Vitamin A is stored in the liver (Ito cells) as **Retinyl palmitate**. * **Teratogenicity:** Retinoic acid is highly teratogenic; pregnancy must be excluded before prescribing Isotretinoin for acne. * **Deficiency:** The earliest symptom is Nyctalopia (night blindness); the earliest physical sign is Conjunctival Xerosis. Bitot’s spots are a pathognomonic sign.

Q: Pyridoxine is essential for the generation of which coenzyme?

NAD (Nicotinamide Adenine Dinucleotide). **Explanation:** The correct answer is **NAD (Nicotinamide Adenine Dinucleotide)** because Pyridoxine (Vitamin B6) plays a crucial role in the **Kynurenine pathway**, which converts the amino acid Tryptophan into Niacin (Vitamin B3). Specifically, the enzyme **Kynureninase** is dependent on **Pyridoxal Phosphate (PLP)**, the active form of Vitamin B6. If B6 is deficient, the conversion of Tryptophan to Niacin is impaired, leading to a decrease in the synthesis of NAD and NADP. **Analysis of Options:** * **Option A (FAD):** This is derived from **Riboflavin (Vitamin B2)**. While B2 is also required in the Kynurenine pathway (for Kynurenine hydroxylase), FAD itself is not generated from Pyridoxine. * **Option B (ATP):** ATP is the primary energy currency of the cell, synthesized via oxidative phosphorylation and substrate-level phosphorylation. It is not a derivative of Pyridoxine. * **Option D:** Incorrect, as the biochemical link between B6 and NAD synthesis is well-established. **Clinical Pearls for NEET-PG:** * **Pellagra-like symptoms:** A deficiency in Vitamin B6 can manifest as secondary Niacin deficiency (Pellagra) because of the failed conversion of Tryptophan to NAD. * **Isoniazid (INH) Therapy:** This anti-tubercular drug is a structural analog of B6. It inhibits the formation of PLP, leading to peripheral neuropathy and potentially Pellagra-like symptoms. Always co-administer B6 with INH. * **Rule of 60:** Approximately **60 mg of Tryptophan** is required to synthesize **1 mg of Niacin**. * **Hartnup Disease:** A defect in neutral amino acid (Tryptophan) transporters can also lead to NAD deficiency, mimicking B6/B3 deficiency.

Q: Activated pantothenic acid is a component of which of the following?

Coenzyme-A. **Explanation:** **1. Why Coenzyme-A is Correct:** Pantothenic acid (Vitamin B5) is the essential precursor for the synthesis of **Coenzyme A (CoA)** and the **Acyl Carrier Protein (ACP)**. The "activated" form refers to its incorporation into the CoA molecule. Structurally, CoA consists of 3'-phosphoadenosine diphosphate linked to pantothenic acid, which is further attached to cysteamine. The functional part of CoA is the terminal thiol (-SH) group, which forms high-energy thioester bonds with acyl groups (e.g., Acetyl-CoA). This makes it indispensable for the TCA cycle, fatty acid synthesis, and fatty acid oxidation. **2. Analysis of Incorrect Options:** * **Option A (GMP):** Guanosine monophosphate is a purine nucleotide. Its synthesis requires amino acids (Glycine, Glutamine, Aspartate) and folic acid derivatives, but not pantothenic acid. * **Option C (G-6-P-D):** This is an enzyme of the HMP shunt. It requires **NADP+** (derived from Vitamin B3/Niacin) as a coenzyme, not CoA. * **Option D (Carboxylation reactions):** These reactions (e.g., Pyruvate carboxylase) typically require **Biotin (Vitamin B7)** as a cofactor to carry CO₂. **3. High-Yield Clinical Pearls for NEET-PG:** * **The "B5" Rule:** Pantothenic acid is Vitamin B5. * **Burning Foot Syndrome:** Deficiency of pantothenic acid is rare but classically manifests as nutritional melalgia (burning sensation in the feet). * **ACP Connection:** Pantothenic acid is a component of the Fatty Acid Synthase multienzyme complex via the Acyl Carrier Protein (ACP) domain. * **Key Intermediate:** Pantothenate must be phosphorylated by *pantothenate kinase* (the rate-limiting step) to begin CoA synthesis.

Q: Which vitamin is essential for both bone formation and the coagulation cascade?

Vitamin K. **Explanation:** **Vitamin K** is the correct answer because it serves as an essential cofactor for the enzyme **$\gamma$-glutamyl carboxylase**. This enzyme catalyzes the post-translational carboxylation of glutamate residues into $\gamma$-carboxyglutamate (Gla) on specific proteins, allowing them to bind calcium. 1. **Coagulation Cascade:** Vitamin K is required for the activation of Clotting Factors **II, VII, IX, and X**, as well as anticoagulant proteins C and S. 2. **Bone Formation:** It is essential for the carboxylation of **Osteocalcin** (Bone Gla Protein) and **Matrix Gla Protein**. Carboxylated osteocalcin has a high affinity for hydroxyapatite, facilitating calcium deposition in the bone matrix. **Analysis of Incorrect Options:** * **Vitamin A:** Primarily involved in vision (rhodopsin), epithelial differentiation, and immune function. While it affects bone remodeling, it is not a cofactor for the coagulation cascade. * **Vitamin D:** Crucial for calcium homeostasis and bone mineralization by increasing intestinal calcium absorption, but it plays no direct role in the enzymatic activation of clotting factors. * **Vitamin E:** Acts as a potent lipid-soluble antioxidant. High doses can actually *interfere* with Vitamin K metabolism, potentially increasing bleeding risk. **High-Yield NEET-PG Pearls:** * **Warfarin Mechanism:** Inhibits **Vitamin K Epoxide Reductase (VKOR)**, preventing the recycling of Vitamin K and thus inhibiting the carboxylation of factors II, VII, IX, and X. * **Newborns:** They are born with sterile guts and low Vitamin K stores; hence, a prophylactic IM injection of Vitamin K is given to prevent **Hemorrhagic Disease of the Newborn**. * **Lab Marker:** Prothrombin Time (PT) is the most sensitive lab test to monitor Vitamin K deficiency.

Q: Which reaction is inhibited in thiamine deficiency?

Pyruvate to acetyl CoA. ### Explanation **Correct Answer: A. Pyruvate to acetyl CoA** **Reasoning:** Thiamine (Vitamin B1) is the precursor for its active form, **Thiamine Pyrophosphate (TPP)**. TPP acts as a vital coenzyme for several multi-enzyme complexes involved in oxidative decarboxylation. One such complex is the **Pyruvate Dehydrogenase (PDH) Complex**, which converts Pyruvate to Acetyl CoA (the link reaction between glycolysis and the TCA cycle). In thiamine deficiency, PDH activity is severely impaired, leading to a buildup of pyruvate, which is then shunted to form lactic acid. **Analysis of Incorrect Options:** * **Option B (Citrate to alpha-ketoglutarate):** This step is catalyzed by *Aconitase* and *Isocitrate Dehydrogenase*. Neither requires TPP. However, the *next* step (alpha-ketoglutarate to succinyl CoA) **does** require TPP. * **Option C (Succinyl CoA to fumarate):** This involves two steps catalyzed by *Succinate Thiokinase* and *Succinate Dehydrogenase*. These enzymes require CoA, GDP, and FAD, but not thiamine. **High-Yield NEET-PG Pearls:** * **Four Key TPP-Dependent Enzymes:** 1. **P**yruvate Dehydrogenase (PDH) 2. **A**lpha-ketoglutarate Dehydrogenase ($\alpha$-KGDH) 3. **B**ranched-chain $\alpha$-ketoacid Dehydrogenase (BCKDH) — deficient in Maple Syrup Urine Disease. 4. **T**ransketolase (HMP Shunt) — used to clinically diagnose thiamine deficiency by measuring erythrocyte transketolase activity. * **Clinical Correlation:** Thiamine deficiency leads to **Beriberi** (Dry: neurological; Wet: cardiac) and **Wernicke-Korsakoff Syndrome** (common in alcoholics). * **Warning:** Always administer thiamine *before* glucose in malnourished patients to prevent precipitating acute Wernicke encephalopathy, as glucose oxidation consumes the remaining thiamine stores.

Question 1

Which of the following is NOT seen in vitamin A deficiency?

Accepted Answer

Polyneuritis

Answer

Night blindness

Answer

Follicular hyperkeratosis

Answer

Growth retardation

Question 2

Generalised edema can be produced by deficiency of which vitamin?

Accepted Answer

Thiamine

Answer

Vitamin A

Answer

Vitamin D

Answer

Folic acid

Question 3

Which of the following is NOT classified under energy-releasing B-complex vitamins?

Accepted Answer

Vitamin B12 (Cobalamin)

Answer

Vitamin B1 (Thiamine)

Answer

Vitamin B2 (Riboflavin)

Answer

Vitamin B6 (Pyridoxine)

Question 4

Bald tongue is seen in deficiency of which vitamin?

Accepted Answer

Niacin

Answer

Riboflavin

Answer

Vitamin B12

Answer

None of the above

Question 5

Which of the following combinations of biologically active molecules does vitamin A consist of?

Accepted Answer

Retinol, retinal, and retinoic acid

Answer

Retinol, retinal, and tetrahydrofolate

Answer

Retinol, iconjugase, and retinoic acid

Answer

PABA, retinal, and retinaldehyde

Question 6

Pyridoxine is essential for the generation of which coenzyme?

Accepted Answer

NAD (Nicotinamide Adenine Dinucleotide)

Answer

FAD (Flavin Adenine Dinucleotide)

Answer

ATP (Adenosine Triphosphate)

Answer

None of the above

Question 7

Activated pantothenic acid is a component of which of the following?

Accepted Answer

Coenzyme-A

Answer

Guanosine monophosphate (GMP)

Answer

Glucose-6-phosphate dehydrogenase (G-6-P-D)

Answer

Carboxylation reactions

Question 8

Which vitamin is essential for both bone formation and the coagulation cascade?

Accepted Answer

Vitamin K

Answer

Vitamin A

Answer

Vitamin D

Answer

Vitamin E

Question 9

Which of the following trace element deficiencies leads to abnormal collagen cross-linking?

Accepted Answer

Copper

Answer

Zinc

Answer

Fluoride

Answer

Selenium

Question 10

Which reaction is inhibited in thiamine deficiency?

Accepted Answer

Pyruvate to acetyl CoA

Answer

Citrate to alpha-ketoglutarate

Answer

Succinyl CoA to fumarate

Answer

None of the above

Vitamins and Coenzymes — MCQs

Vitamins and Coenzymes — MCQs

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