Vitamins and Coenzymes Practice Questions

Q: Which vitamin deficiency causes glossitis and cheilosis?

Riboflavin. **Explanation:** **Riboflavin (Vitamin B2)** is the correct answer because its deficiency specifically manifests as **Ariboflavinosis**. This clinical syndrome is characterized by mucosal and epithelial changes, most notably **glossitis** (magenta-colored tongue), **cheilosis** (fissuring of the lips), and **angular stomatitis** (cracks at the corners of the mouth). Riboflavin is a precursor for FMN and FAD, which are essential for redox reactions in energy metabolism; tissues with high turnover rates, like the oral mucosa, are the first to show signs of deficiency. **Analysis of Incorrect Options:** * **Thiamin (B1):** Deficiency primarily leads to **Beriberi** (Dry: peripheral neuropathy; Wet: high-output heart failure) or **Wernicke-Korsakoff syndrome** in alcoholics. It does not typically present with isolated cheilosis. * **Folic Acid (B9):** While deficiency can cause glossitis, its hallmark is **megaloblastic anemia** and neural tube defects. It is not the classic cause of the "cheilosis-glossitis" dyad associated with B2. * **Vitamin A:** Deficiency is primarily associated with ocular symptoms such as **Nyctalopia** (night blindness), Xerophthalmia, and Bitot’s spots, or skin changes like follicular hyperkeratosis. **High-Yield Clinical Pearls for NEET-PG:** * **Magenta Tongue:** A classic buzzword for Riboflavin deficiency (distinguish from the "Beefy Red" tongue of B12/Niacin deficiency). * **Corneal Neovascularization:** Another specific sign of B2 deficiency often tested alongside oral symptoms. * **Enzyme Link:** Riboflavin is required by **Glutathione Reductase**; its activity in RBCs is used to biochemically diagnose B2 deficiency.

Q: What is the similarity between Vitamin C and Vitamin K?

Both are involved in post-translational modification.. **Explanation:** The correct answer is **B. Both are involved in post-translational modification.** Post-translational modification refers to the chemical modification of a protein after its synthesis on the ribosome. Both Vitamin C and Vitamin K act as essential cofactors for enzymes that modify specific amino acid residues: 1. **Vitamin C (Ascorbic Acid):** Acts as a coenzyme for **prolyl hydroxylase** and **lysyl hydroxylase**. It facilitates the hydroxylation of proline and lysine residues in procollagen. This is crucial for the cross-linking and structural stability of triple-helical collagen. 2. **Vitamin K:** Acts as a cofactor for **$\gamma$-glutamyl carboxylase**. It is essential for the carboxylation of glutamate residues to $\gamma$-carboxyglutamate (Gla) on proteins like Factors II, VII, IX, X, and Proteins C and S. This modification allows these proteins to bind calcium and anchor to phospholipid membranes. **Analysis of Incorrect Options:** * **Option A:** This describes the specific function of **Vitamin C** only. Vitamin K does not affect proline hydroxylation. * **Option C:** **Vitamin A** is traditionally known as the "anti-infective" vitamin due to its role in maintaining epithelial integrity and immune function. * **Option D:** This is the specific function of **Vitamin K**. Vitamin C deficiency leads to scurvy (bleeding gums/petechiae) due to capillary fragility, but it is not a part of the enzymatic coagulation cascade. **NEET-PG High-Yield Pearls:** * **Vitamin C:** Deficiency leads to **Scurvy** (corkscrew hair, easy bruising, poor wound healing). It also aids in **Iron absorption** (reduces $Fe^{3+}$ to $Fe^{2+}$). * **Vitamin K:** Antagonized by **Warfarin**. It is necessary for the synthesis of "1972" factors (10, 9, 7, 2). Newborns receive a prophylactic dose because breast milk is low in Vitamin K and their sterile guts cannot synthesize it.

Q: Keshan disease is seen in deficiency of which element?

Selenium. **Explanation:** **Keshan disease** is a congestive cardiomyopathy primarily caused by a deficiency of **Selenium**. It was first identified in the Keshan province of China, where the soil is notoriously low in this trace element. **Why Selenium is the correct answer:** Selenium is a vital component of the enzyme **Glutathione Peroxidase**, which protects cells from oxidative damage by neutralizing hydrogen peroxide. In selenium deficiency, the antioxidant defense system fails, leading to lipid peroxidation and subsequent myocardial necrosis and fibrosis. While selenium deficiency is the primary trigger, it often acts in synergy with a viral trigger (like the Coxsackievirus B) to manifest as cardiomyopathy. **Why other options are incorrect:** * **Chromium:** Deficiency is associated with **impaired glucose tolerance** and insulin resistance, as chromium is a component of the Glucose Tolerance Factor (GTF). * **Molybdenum:** It is a cofactor for enzymes like Xanthine Oxidase and Sulfite Oxidase. Deficiency is rare but can lead to neurological abnormalities and lens dislocation. * **Copper:** Deficiency leads to **Menkes Kinky Hair Syndrome**, microcytic anemia, and skeletal abnormalities. It is a cofactor for Lysyl Oxidase and Cytochrome c Oxidase. **High-Yield Clinical Pearls for NEET-PG:** * **Kashin-Beck Disease:** Another selenium deficiency disorder characterized by osteoarthropathy (cartilage degeneration). * **Selenocysteine:** Known as the **21st amino acid**, it is the form in which selenium is incorporated into proteins (Selenoproteins). * **Toxicity:** Excess selenium (Selenosis) causes garlic breath, hair loss (alopecia), and nail dystrophy.

Q: Avidin influences which of the following vitamins?

Biotin. **Explanation:** The correct answer is **A. Biotin (Vitamin B7)**. **Why Biotin is correct:** Avidin is a heat-labile glycoprotein found in **raw egg whites**. It has an extraordinarily high affinity for Biotin. When consumed, avidin binds tightly to biotin in the gastrointestinal tract, forming a non-absorbable complex that prevents the vitamin's absorption. This can lead to "egg white injury," characterized by dermatitis, alopecia, and neurological symptoms. Cooking denatures avidin, rendering it unable to bind biotin. **Why other options are incorrect:** * **Niacin (B3):** Its deficiency (Pellagra) is associated with maize-based diets (low tryptophan) or Hartnup disease, not avidin. * **Thiamine (B1):** Deficiency is typically linked to chronic alcoholism or polished rice diets, leading to Beriberi or Wernicke-Korsakoff syndrome. * **Phylloquinone (K1):** This is a fat-soluble vitamin involved in blood clotting. Its absorption is influenced by bile salts and fat intake, not egg white proteins. **High-Yield Clinical Pearls for NEET-PG:** 1. **Biochemical Role:** Biotin acts as a coenzyme for **carboxylation reactions** (e.g., Pyruvate carboxylase, Acetyl-CoA carboxylase, and Propionyl-CoA carboxylase). 2. **The "CO2 Carrier":** Biotin functions as a carrier of activated carbon dioxide. 3. **Clinical Presentation:** To develop a deficiency via diet, a patient must consume a massive amount of raw egg whites (e.g., 12–20 per day) over a prolonged period. 4. **Valproate Link:** Long-term use of the anticonvulsant Valproate can sometimes interfere with biotinidase activity, leading to functional biotin deficiency.

Q: Post-translational modification of lysine and proline is facilitated by which vitamin?

Vitamin C. **Explanation:** **Vitamin C (Ascorbic Acid)** is the correct answer because it acts 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 during **collagen synthesis**. The underlying biochemical mechanism involves the reduction of ferric iron ($Fe^{3+}$) back to the active ferrous state ($Fe^{2+}$) within the enzyme's active site. This hydroxylation is essential for the formation of stable triple-helical collagen fibers; without it, collagen fibers lack tensile strength and are easily degraded. **Why other options are incorrect:** * **Vitamin A:** Primarily involved in vision (retinal), gene transcription (retinoic acid), and epithelial cell differentiation, not collagen hydroxylation. * **Vitamin B1 (Thiamine):** Acts as a coenzyme (TPP) for oxidative decarboxylation reactions (e.g., Pyruvate Dehydrogenase) and the HMP shunt (Transketolase). * **Vitamin D:** Functions as a hormone regulating calcium and phosphate homeostasis and bone mineralization. **High-Yield Clinical Pearls for NEET-PG:** * **Scurvy:** Deficiency of Vitamin C leads to defective collagen synthesis, manifesting as "corkscrew hair," petechiae, splinter hemorrhages, and **swollen, bleeding gums**. * **Wound Healing:** Vitamin C is critical for the proliferative phase of wound healing due to its role in collagen cross-linking. * **Iron Absorption:** Vitamin C enhances the absorption of non-heme iron from the gut by maintaining it in the ferrous ($Fe^{2+}$) state. * **Antioxidant:** It is a potent water-soluble antioxidant that regenerates Vitamin E.

Q: What is the active form of vitamin D?

1, 25-dihydroxyvitamin D. **Explanation:** The active form of Vitamin D is **1, 25-dihydroxyvitamin D**, also known as **Calcitriol**. Vitamin D synthesis is a multi-step process. In the skin, 7-dehydrocholesterol is converted to Cholecalciferol (Vitamin D3) by UV light. This undergoes two essential hydroxylations: 1. **First Hydroxylation:** Occurs in the **Liver** by the enzyme 25-hydroxylase to form 25-hydroxyvitamin D [25(OH)D]. 2. **Second Hydroxylation:** Occurs in the **Kidney** (proximal convoluted tubule) by the enzyme **1α-hydroxylase** to form 1, 25-dihydroxyvitamin D. This is the biologically active hormone that binds to nuclear receptors to regulate calcium and phosphate homeostasis. **Analysis of Options:** * **Option A (Cholecalciferol):** This is the inactive precursor synthesized in the skin or ingested; it has no biological activity until hydroxylated. * **Option B (24, 25-dihydroxyvitamin D):** This is an **inactive metabolite** formed when 1α-hydroxylase is inhibited. It is the body's way of diverting Vitamin D away from the active form when calcium levels are sufficient. * **Option D (25-hydroxyvitamin D):** Known as **Calcidiol**, this is the major **circulating form** and the best indicator of a patient’s overall Vitamin D status (nutritional reserve), but it is not the active form. **High-Yield NEET-PG Pearls:** * **Rate-limiting step:** The 1α-hydroxylation in the kidney is the most tightly regulated step, stimulated by **PTH** and low serum phosphate. * **Storage:** Vitamin D is stored primarily in **adipose tissue**. * **Clinical Marker:** Always measure **25(OH)D** to diagnose deficiency, not Calcitriol, due to its longer half-life.

Q: Thiamine acts as a cofactor in which of the following reactions?

Conversion of pyruvate to acetyl-CoA. **Explanation:** **1. Why Option A is Correct:** Thiamine (Vitamin B1) is converted into its active form, **Thiamine Pyrophosphate (TPP)**. TPP acts as a crucial cofactor for enzymes involved in oxidative decarboxylation. The conversion of **Pyruvate to Acetyl-CoA** is catalyzed by the **Pyruvate Dehydrogenase (PDH) complex**, which requires TPP (along with FAD, NAD, CoA, and Lipoic acid). TPP is also a cofactor for: * $\alpha$-ketoglutarate dehydrogenase (TCA cycle) * Branched-chain $\alpha$-ketoacid dehydrogenase (BCAA metabolism) * Transketolase (HMP Shunt) **2. Why Other Options are Incorrect:** * **Option B:** Transamination reactions require **Pyridoxal Phosphate (PLP)**, the active form of Vitamin B6. * **Option C:** Oxidation in the respiratory chain (Electron Transport Chain) primarily utilizes **FAD/FMN** (derived from Vitamin B2/Riboflavin) and **NAD/NADP** (derived from Vitamin B3/Niacin) as electron carriers. * **Option D:** The conversion of pyridoxal to pyridoxal phosphate is a phosphorylation reaction catalyzed by pyridoxal kinase, requiring ATP, not thiamine. **3. High-Yield Clinical Pearls for NEET-PG:** * **Wernicke-Korsakoff Syndrome:** Characterized by the triad of ataxia, ophthalmoplegia, and confusion. It is common in chronic alcoholics due to thiamine deficiency. * **Beriberi:** "Dry" beriberi involves peripheral neuropathy; "Wet" beriberi involves high-output heart failure. * **Diagnostic Marker:** Erythrocyte **transketolase activity** is the most reliable biochemical test to assess thiamine status. * **Clinical Rule:** Always administer thiamine *before* glucose in malnourished patients to prevent precipitating Wernicke encephalopathy (as glucose oxidation consumes remaining thiamine).

Q: Zinc deficiency causes which of the following conditions?

Acrodermatitis enteropathica. **Explanation:** **1. Why Acrodermatitis Enteropathica is Correct:** Acrodermatitis enteropathica (AE) is the classic clinical manifestation of severe **Zinc deficiency**. It can be inherited (autosomal recessive mutation in the *SLC39A4* gene, which encodes a zinc transporter) or acquired (due to malnutrition or malabsorption). Zinc is a vital cofactor for over 300 enzymes, including Carbonic Anhydrase and Alkaline Phosphatase. Deficiency leads to the characteristic triad of **periorificial and acral dermatitis** (rash around the mouth, anus, and limbs), **alopecia**, and **diarrhea**. **2. Analysis of Incorrect Options:** * **B. Scaly dermatitis:** While zinc deficiency involves skin changes, "scaly dermatitis" is a non-specific term. However, it is specifically associated with **Vitamin B6 (Pyridoxine)** or **Biotin** deficiency. * **C. Follicular keratosis:** Also known as "Phrynoderma" (toad skin), this is a hallmark of **Vitamin A deficiency** (and sometimes Vitamin C or essential fatty acids). * **D. Skeletal fluorosis:** This is caused by **chronic fluoride toxicity** (excess), not a deficiency. It leads to increased bone density and calcification of ligaments. **3. High-Yield Clinical Pearls for NEET-PG:** * **Zinc & Wound Healing:** Zinc is essential for DNA synthesis and cell division; deficiency causes **delayed wound healing** and **hypogeusia** (decreased taste acuity). * **Immunity:** Zinc is crucial for T-lymphocyte function; deficiency leads to cell-mediated immune dysfunction. * **Growth:** In children, zinc deficiency is a major cause of **growth retardation** and hypogonadism. * **Enzyme Marker:** Serum **Alkaline Phosphatase** levels often decrease in zinc deficiency as it is a zinc-dependent enzyme.

Question 1

Which vitamin deficiency causes glossitis and cheilosis?

Accepted Answer

Riboflavin

Answer

Thiamin

Answer

Folic acid

Answer

Vitamin A

Question 2

What is the similarity between Vitamin C and Vitamin K?

Accepted Answer

Both are involved in post-translational modification.

Answer

Both aid in the conversion of proline to hydroxyproline.

Answer

Both possess anti-infective activity.

Answer

Both are involved in the coagulation cascade.

Question 3

Keshan disease is seen in deficiency of which element?

Accepted Answer

Selenium

Answer

Chromium

Answer

Molybdenum

Answer

Copper

Question 4

What is the primary function of cyanocobalamin?

Accepted Answer

A coenzyme for one-carbon transfer in nucleic acid metabolism

Answer

Post-translational carboxylation of proteins

Answer

Acts as coenzymes for methionine synthase and L-methylmalonyl-CoA synthase

Answer

A cofactor for decarboxylation of ketoacids

Question 5

Which of the following is the least useful anti-rachitic agent?

Accepted Answer

Cholecalciferol

Answer

1,25-dihydroxycholecalciferol (calcitriol)

Answer

25-hydroxycholecalciferol

Answer

Calcium

Question 6

Avidin influences which of the following vitamins?

Accepted Answer

Biotin

Answer

Niacin

Answer

Thiamine

Answer

Phylloquinone

Question 7

Post-translational modification of lysine and proline is facilitated by which vitamin?

Accepted Answer

Vitamin C

Answer

Vitamin A

Answer

Vitamin B1

Answer

Vitamin D

Question 8

What is the active form of vitamin D?

Accepted Answer

1, 25-dihydroxyvitamin D

Answer

Cholecalciferol

Answer

24, 25-dihydroxyvitamin D

Answer

25-hydroxyvitamin D

Question 9

Thiamine acts as a cofactor in which of the following reactions?

Accepted Answer

Conversion of pyruvate to acetyl-CoA

Answer

Transamination reactions

Answer

Oxidation in the respiratory chain

Answer

Conversion of pyridoxal to pyridoxal phosphate

Question 10

Zinc deficiency causes which of the following conditions?

Accepted Answer

Acrodermatitis enteropathica

Answer

Scaly dermatitis

Answer

Follicular keratosis

Answer

Skeletal fluorosis

Vitamins and Coenzymes — MCQs

Vitamins and Coenzymes — MCQs

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