Vitamins and Coenzymes Practice Questions

Q: Which vitamin deficiency is commonly seen in alcoholic patients presenting with dementia?

Thiamine. **Explanation:** **Thiamine (Vitamin B1) deficiency** is the hallmark of chronic alcoholism. Alcohol interferes with thiamine absorption from the gut and impairs its conversion into its active form, **Thiamine Pyrophosphate (TPP)**. TPP is a critical coenzyme for enzymes like pyruvate dehydrogenase and α-ketoglutarate dehydrogenase. Deficiency leads to **Wernicke-Korsakoff Syndrome**. While Wernicke’s encephalopathy presents with the triad of ataxia, ophthalmoplegia, and confusion, **Korsakoff psychosis** is characterized by permanent cognitive impairment (dementia), profound anterograde amnesia, and **confabulation** (making up stories to fill memory gaps). **Why other options are incorrect:** * **Vitamin B12 (Cobalamin):** Deficiency causes Subacute Combined Degeneration of the spinal cord and megaloblastic anemia. While it can cause "megaloblastic madness" or dementia, it is less specifically associated with the acute/subacute presentation in alcoholics compared to Thiamine. * **Riboflavin (B2):** Deficiency typically presents with cheilosis, glossitis, and corneal vascularization, not dementia. * **Pyridoxine (B6):** Deficiency is often associated with Isoniazid (INH) therapy and presents with peripheral neuropathy or sideroblastic anemia. **NEET-PG High-Yield Pearls:** * **Enzyme Marker:** Erythrocyte **transketolase** activity is the most reliable biochemical test to diagnose thiamine deficiency. * **Clinical Rule:** Always administer Thiamine **before** Glucose in an alcoholic patient to prevent precipitating acute Wernicke’s encephalopathy. * **Brain Pathology:** Look for atrophy or hemorrhage in the **mammillary bodies** on MRI.

Q: Which vitamin is required for the carboxylation of clotting factors?

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 modification of specific glutamic acid residues into **gamma-carboxyglutamic acid (Gla)**. This carboxylation is vital for the activation of clotting factors **II, VII, IX, and X**, as well as anticoagulant proteins **C and S**. The addition of the carboxyl group allows these proteins to bind calcium ions ($Ca^{2+}$), which facilitates their binding to phospholipid membranes—a critical step in the coagulation cascade. **Why other options are incorrect:** * **Vitamin A:** Primarily involved in vision (rhodopsin formation), epithelial integrity, and gene transcription. * **Vitamin D:** Regulates calcium and phosphate homeostasis and bone mineralization. * **Vitamin E:** Acts as a potent lipid-soluble antioxidant, protecting cell membranes from oxidative damage; it does not participate in carboxylation. **High-Yield Clinical Pearls for NEET-PG:** * **Warfarin Mechanism:** Warfarin acts as a Vitamin K antagonist by inhibiting **Vitamin K Epoxide Reductase (VKOR)**, preventing the regeneration of active Vitamin K (hydroquinone). * **Newborn Prophylaxis:** Neonates are born with sterile guts and low Vitamin K stores; hence, a prophylactic IM injection of Vitamin K is given at birth to prevent **Hemorrhagic Disease of the Newborn**. * **Lab Findings:** Vitamin K deficiency leads to an increased **Prothrombin Time (PT)** and International Normalized Ratio (INR). * **Other Gla Proteins:** Osteocalcin (in bone) also requires Vitamin K for carboxylation.

Q: Thiamine is NOT used in which of the following biochemical reactions?

Lactate to pyruvate. **Explanation:** Thiamine (Vitamin B1), in its active form **Thiamine Pyrophosphate (TPP)**, acts as a critical coenzyme for enzymes involved in oxidative decarboxylation and the pentose phosphate pathway. **1. Why Option A is correct:** The conversion of **Lactate to Pyruvate** is catalyzed by the enzyme **Lactate Dehydrogenase (LDH)**. This is a redox reaction that requires **NAD+** as a coenzyme, not TPP. Thiamine is not involved in this step. In fact, in thiamine deficiency, pyruvate cannot enter the TCA cycle and is instead shunted toward lactate production, leading to lactic acidosis. **2. Analysis of Incorrect Options:** * **Option B:** The conversion of **Alpha-ketoglutarate to Succinyl CoA** is catalyzed by the *α-ketoglutarate dehydrogenase complex*, which requires TPP (along with FAD, NAD, CoA, and Lipoate). * **Option C:** The conversion of **Glucose to Pentose** (Pentose Phosphate Pathway) requires the enzyme *Transketolase*, which is strictly TPP-dependent. Measuring erythrocyte transketolase activity is a functional test for thiamine status. * **Option D:** **Oxidative decarboxylation of branched-chain α-keto acids** (derived from Valine, Leucine, and Isoleucine) is catalyzed by the *Branched-chain α-keto acid dehydrogenase complex*, which also requires TPP. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for TPP-dependent enzymes:** "**A**TP" (**A**lpha-ketoglutarate dehydrogenase, **T**ransketolase, **P**yruvate dehydrogenase). * **Clinical Deficiency:** Wernicke-Korsakoff syndrome (triad of ataxia, ophthalmoplegia, and confusion) and Beriberi (Dry = polyneuritis; Wet = high-output heart failure). * **Biochemical Marker:** In thiamine deficiency, blood lactate and pyruvate levels are elevated.

Q: A 30-year-old female patient complains of weakness and fatigue. The patient has a history of consuming antiepileptic drugs and is also a lactating mother. Laboratory investigations reveal Hb of 8 gm% and the presence of macrocytic RBCs on peripheral blood smear. This patient may be suffering from a deficiency of?

Vitamin B9 (Folate). ### Explanation The correct answer is **Vitamin B9 (Folate)**. **1. Why Vitamin B9 (Folate) is correct:** The patient presents with **Macrocytic Anemia** (Hb 8 gm%, macrocytic RBCs). Folate (Vitamin B9) is essential for one-carbon metabolism and DNA synthesis. Its deficiency impairs erythropoiesis, leading to the production of large, immature RBCs (megaloblasts). * **Antiepileptic Drugs (AEDs):** Drugs like Phenytoin, Phenobarbital, and Primidone interfere with folate absorption or metabolism, making users highly susceptible to deficiency. * **Lactation:** This is a high-demand physiological state where folate requirements increase significantly to support the infant and the mother's metabolic needs. The combination of AEDs and lactation creates a "perfect storm" for folate depletion. **2. Why other options are incorrect:** * **Vitamin C:** Deficiency leads to Scurvy (bleeding gums, petechiae). While it aids iron absorption, its deficiency typically causes microcytic or normocytic anemia, not macrocytic. * **Vitamin B1 (Thiamine):** Deficiency causes Beriberi (Wet/Dry) or Wernicke-Korsakoff syndrome. It does not cause macrocytic anemia. * **Vitamin B2 (Riboflavin):** Deficiency presents with cheilosis, glossitis, and seborrheic dermatitis, but not macrocytic anemia. **3. NEET-PG High-Yield Pearls:** * **Drug-Induced Folate Deficiency:** Always look for **Phenytoin, Methotrexate, or Trimethoprim** in the history. * **Folate vs. B12:** Both cause macrocytic anemia. However, Folate deficiency **does not** present with neurological symptoms (subacute combined degeneration), whereas B12 deficiency does. * **Storage:** Folate stores in the liver last only **3–4 months**, whereas Vitamin B12 stores last **3–5 years**. * **FIGLU Test:** Histidine load test (FIGLU excretion in urine) is a specific biochemical marker for Folate deficiency.

Q: Peripheral neuropathy is seen with the deficiency of which vitamin?

Pyridoxine. **Explanation:** **Pyridoxine (Vitamin B6)** is the correct answer because it is essential for the synthesis of neurotransmitters (such as GABA, dopamine, and serotonin) and the formation of sphingolipids required for myelin sheath integrity. Its deficiency leads to axonal degeneration, manifesting as **peripheral neuropathy**. A high-yield clinical association for NEET-PG is **Isoniazid (INH)** therapy for Tuberculosis. INH inhibits the enzyme pyridoxine phosphokinase and increases the renal excretion of B6, leading to induced deficiency. Therefore, B6 is always co-prescribed with INH to prevent neuropathy. **Analysis of Incorrect Options:** * **Vitamin E:** While deficiency can cause neurological symptoms (ataxia, loss of proprioception, and hemolytic anemia), it primarily presents as a **spinocerebellar degeneration** rather than isolated peripheral neuropathy. * **Vitamin A:** Deficiency primarily affects vision (**Nyctalopia**, Xerophthalmia) and epithelial integrity (Bitot’s spots, follicular hyperkeratosis), not the peripheral nerves. * **Pantothenic acid (B5):** Deficiency is extremely rare but is classically associated with **"Burning Foot Syndrome"** (Gopalan’s syndrome). While this involves the feet, Pyridoxine is the more standard answer for generalized peripheral neuropathy in a clinical/biochemical context. **Clinical Pearls for NEET-PG:** 1. **Sideroblastic Anemia:** B6 deficiency also causes microcytic anemia because it is a cofactor for **ALA synthase**, the rate-limiting step in heme synthesis. 2. **Homocysteinemia:** B6 is a cofactor for **Cystathionine beta-synthase**; deficiency leads to elevated homocysteine levels (a risk factor for thrombosis). 3. **Dependency States:** Infantile convulsions can occur in B6 dependency states due to decreased GABA levels.

Q: Which of the following forms of Vitamin A has maximum effects on DNA?

Isotretinoin. **Explanation:** The biological effects of Vitamin A on gene expression are mediated primarily by its acidic forms, known as **Retinoic Acids**. **1. Why Isotretinoin is correct:** Vitamin A acts as a hormone-like signal. Retinol is oxidized into Retinaldehyde and then into Retinoic Acid (RA). **Isotretinoin (13-cis-retinoic acid)** and its isomer, Tretinoin (all-trans-retinoic acid), are the active metabolites that enter the nucleus. They bind to specific nuclear receptors: **RAR (Retinoic Acid Receptor)** and **RXR (Retinoid X Receptor)**. These receptors act as ligand-activated transcription factors that bind to **RARE (Retinoic Acid Response Elements)** on the DNA, directly regulating the transcription of genes responsible for cell growth and differentiation. **2. Why the other options are incorrect:** * **Retinol:** This is the transport form of Vitamin A (bound to Retinol Binding Protein). It must be converted into retinoic acid to exert genomic effects. * **Retinaldehyde (Retinal):** This is the aldehyde form essential for the **visual cycle** (forming Rhodopsin). While vital for vision, it does not directly modulate DNA transcription. * **Isoretinal:** This is not a standard physiological form involved in gene regulation; it is likely a distractor term. **High-Yield Clinical Pearls for NEET-PG:** * **Teratogenicity:** Because retinoic acid (Isotretinoin) directly alters DNA expression, it is highly teratogenic. A negative pregnancy test and contraception are mandatory before prescribing it for acne. * **Therapeutic Use:** All-trans-retinoic acid (ATRA) is the first-line treatment for **Acute Promyelocytic Leukemia (M3)** as it induces differentiation of leukemic cells. * **Storage:** Vitamin A is stored in the liver in **Ito cells** (Stellate cells) as Retinyl palmitate.

Q: Which of the following can cause dysphonia and hoarseness of voice?

Thiamine. **Explanation:** **Thiamine (Vitamin B1) Deficiency** is the correct answer because it can lead to **Infantile Beriberi**, specifically the **aphonic form**. In infants (usually 2–6 months old) born to thiamine-deficient mothers, the deficiency manifests as a characteristic "silent cry." This occurs due to **laryngeal nerve paralysis** or edema of the larynx, resulting in dysphonia, hoarseness, or a complete loss of voice (aphonia). In adults, severe chronic deficiency (Dry Beriberi) can also cause peripheral neuropathy involving cranial nerves, potentially affecting vocal cord function. **Incorrect Options:** * **Pyridoxine (B6):** Deficiency typically presents with microcytic anemia, seborrheic dermatitis, and neurological symptoms like convulsions (due to decreased GABA) or peripheral neuropathy, but not specific laryngeal nerve involvement. * **Vitamin B12 (Cobalamin):** Deficiency leads to Megaloblastic anemia and Subacute Combined Degeneration of the Spinal Cord (SCDSC). While it causes neurological deficits, it primarily affects the posterior and lateral columns, not the recurrent laryngeal nerve. * **Folic Acid (B9):** Deficiency causes Megaloblastic anemia and neural tube defects in fetuses. It does not have a direct association with vocal cord paralysis or dysphonia. **High-Yield Clinical Pearls for NEET-PG:** * **Wet Beriberi:** High-output cardiac failure + Edema. * **Dry Beriberi:** Symmetrical peripheral neuropathy (wasting and weakness). * **Wernicke-Korsakoff Syndrome:** Triad of Confusion, Ataxia, and Ophthalmoplegia (often seen in alcoholics). * **Key Enzyme:** Thiamine pyrophosphate (TPP) is a cofactor for **Pyruvate Dehydrogenase** and **Alpha-ketoglutarate dehydrogenase**. Its activity is measured via the **Erythrocyte Transketolase** assay.

Q: What is the richest source of Vitamin A?

Halibut liver oil. **Explanation:** Vitamin A (Retinol) is a fat-soluble vitamin essential for vision, epithelial integrity, and immune function. The correct answer is **Halibut liver oil** because it contains the highest concentration of preformed Vitamin A (Retinol). **1. Why Halibut liver oil is correct:** Animal-derived sources provide Vitamin A in the form of **Retinyl esters**. Among these, fish liver oils are the most concentrated sources. While Cod liver oil is a well-known source, **Halibut liver oil** and **Shark liver oil** contain significantly higher concentrations of the vitamin per unit weight, making Halibut the "richest" source among the options provided. **2. Analysis of Incorrect Options:** * **Carrot:** This is a rich source of **Beta-carotene** (a provitamin). However, the conversion of beta-carotene to active retinol in the human body is inefficient (6:1 ratio). Therefore, plant sources are never "richer" than concentrated animal oils. * **Butter:** While butter is a good source of Vitamin A, its concentration is much lower compared to fish liver oils. * **Margarine:** This is a vegetable oil-based product. It does not naturally contain Vitamin A and is usually **fortified** with it to match the nutritional profile of butter. **Clinical Pearls for NEET-PG:** * **Storage:** Vitamin A is stored in the **Ito cells** (Stellate cells) of the liver. * **Deficiency:** The earliest clinical sign is **Nyctalopia** (Night blindness). The earliest objective sign is **Conjunctival Xerosis**. * **Bitot’s Spots:** Triangular, pearly-white foamy plaques on the bulbar conjunctiva, pathognomonic for Vitamin A deficiency. * **Toxicity:** Hypervitaminosis A can lead to **Pseudotumor cerebri** (idiopathic intracranial hypertension). * **Golden Rice:** A genetically modified variety of rice produced to biosynthesize beta-carotene to prevent deficiency in developing countries.

Q: Korsakoff psychosis is typically seen in which of the following conditions?

Thiamine deficiency. **Explanation:** **Korsakoff psychosis** is a late-stage manifestation of **Thiamine (Vitamin B1)** deficiency, often occurring as a sequel to Wernicke encephalopathy (together known as Wernicke-Korsakoff Syndrome). Thiamine, in its active form **Thiamine Pyrophosphate (TPP)**, is a crucial coenzyme for key enzymes in carbohydrate metabolism: Pyruvate Dehydrogenase, $\alpha$-ketoglutarate dehydrogenase, and Transketolase. In chronic deficiency (commonly due to alcoholism), the brain's inability to utilize glucose leads to neuronal damage, specifically in the **mammillary bodies** and dorsomedial nucleus of the thalamus. Korsakoff psychosis is characterized by anterograde amnesia and **confabulation** (filling memory gaps with fabricated stories). **Analysis of Incorrect Options:** * **Riboflavin (B2) deficiency:** Presents as "Ariboflavinosis," characterized by cheilosis, glossitis, corneal vascularization, and seborrheic dermatitis. * **Niacin (B3) deficiency:** Causes **Pellagra**, characterized by the "3 Ds": Dermatitis (Casal’s necklace), Diarrhea, and Dementia. While it involves cognitive decline, it does not present with the specific confabulatory amnesia of Korsakoff. * **Cyanocobalamin (B12) deficiency:** Leads to Megaloblastic anemia and **Subacute Combined Degeneration (SCD)** of the spinal cord, affecting the posterior and lateral columns. **High-Yield Clinical Pearls for NEET-PG:** * **Wernicke’s Encephalopathy Triad:** Confusion, Ataxia, and Ophthalmoplegia (reversible with Thiamine). * **Korsakoff Psychosis:** Irreversible memory loss and confabulation. * **Diagnostic Test:** Measurement of **Erythrocyte Transketolase activity** (increases after adding TPP). * **Management Rule:** Always administer Thiamine *before* Glucose in a malnourished patient to prevent precipitating Wernicke’s.

Question 1

Which vitamin deficiency is commonly seen in alcoholic patients presenting with dementia?

Accepted Answer

Thiamine

Answer

Vitamin B12

Answer

Riboflavin

Answer

Pyridoxine

Question 2

Which vitamin is required for the carboxylation of clotting factors?

Accepted Answer

Vitamin K

Answer

Vitamin A

Answer

Vitamin D

Answer

Vitamin E

Question 3

Thiamine is NOT used in which of the following biochemical reactions?

Accepted Answer

Lactate to pyruvate

Answer

Alpha-ketoglutarate to succinyl CoA

Answer

Glucose to pentose

Answer

Oxidative decarboxylation of alpha-keto amino acids

Question 4

A 30-year-old female patient complains of weakness and fatigue. The patient has a history of consuming antiepileptic drugs and is also a lactating mother. Laboratory investigations reveal Hb of 8 gm% and the presence of macrocytic RBCs on peripheral blood smear. This patient may be suffering from a deficiency of?

Accepted Answer

Vitamin B9 (Folate)

Answer

Vitamin C

Answer

Vitamin B1 (Thiamine)

Answer

Vitamin B2 (Riboflavin)

Question 5

Peripheral neuropathy is seen with the deficiency of which vitamin?

Accepted Answer

Pyridoxine

Answer

Vitamin E

Answer

Vitamin A

Answer

Pantothenic acid

Question 6

Which of the following forms of Vitamin A has maximum effects on DNA?

Accepted Answer

Isotretinoin

Answer

Isoretinal

Answer

Retinaldehyde

Answer

Retinol

Question 7

Which of the following can cause dysphonia and hoarseness of voice?

Accepted Answer

Thiamine

Answer

Pyridoxine

Answer

Vitamin B12

Answer

Folic Acid

Question 8

Niacin deficiency in a maize-eating population is due to which of the following factors?

Accepted Answer

High Leucine

Answer

High Tryptophan

Answer

High Isoleucine

Answer

High Phenylalanine

Question 9

What is the richest source of Vitamin A?

Accepted Answer

Halibut liver oil

Answer

Carrot

Answer

Butter

Answer

Margarine

Question 10

Korsakoff psychosis is typically seen in which of the following conditions?

Accepted Answer

Thiamine deficiency

Answer

Riboflavin deficiency

Answer

Niacin deficiency

Answer

Cyanocobalamin deficiency

Vitamins and Coenzymes — MCQs

Vitamins and Coenzymes — MCQs

On this page

Practice by Chapter

Want unlimited practice?