Vitamins and Coenzymes — MCQs
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Consider the following statements: 1. Diets high in vitamin C have been claimed to lower the incidence of certain cancers, particularly oesophageal and gastric cancers. 2. Vitamin C can prevent the conversion of nitrites and secondary amines to carcinogenic nitrosamines. Which of the statements given above is/are correct?
Consider the following statements regarding folic acid: 1. It is needed for normal development of blood cells in the marrow 2. It has a role in synthesis of nucleic acids 3. It is resistant to boiling Which of the above statements is/are correct?
Major source of vitamin K1 is:
Xanthurenic aciduria is seen in which vitamin deficiency?
Methyl-tetrahydrofolate (5-methyl-THF) gets accumulated in deficiency of which of the following?
Most potent lipid phase antioxidant:
Which enzyme level is tested in thiamine deficiency?
Wernicke's encephalopathy is due to deficiency of:
Wernicke-Korsakoff's syndrome is due to the deficiency of:
Vitamin K leads to?
Vitamins and Coenzymes Indian Medical PG Practice Questions and MCQs
Question 701: Consider the following statements: 1. Diets high in vitamin C have been claimed to lower the incidence of certain cancers, particularly oesophageal and gastric cancers. 2. Vitamin C can prevent the conversion of nitrites and secondary amines to carcinogenic nitrosamines. Which of the statements given above is/are correct?
- A. 1 only
- B. 2 only
- C. Both 1 and 2 (Correct Answer)
- D. Neither 1 nor 2
Explanation: ***Both 1 and 2*** - **Statement 1 is correct:** Epidemiological studies have consistently shown that diets high in vitamin C are associated with a **lower incidence of oesophageal and gastric cancers**, attributed to its antioxidant properties and protective mechanisms. - **Statement 2 is correct:** Vitamin C acts as a **reducing agent that blocks nitrosamine formation** by preventing nitrites and secondary amines from reacting to form these carcinogenic compounds in the acidic gastric environment. - Both statements are **independently true and complementary** - statement 2 explains one of the key mechanisms by which statement 1's observation occurs. *1 only* - This option is incorrect because it ignores statement 2, which describes a **well-established biochemical mechanism** of vitamin C's cancer-protective effect. - The ability of vitamin C to prevent nitrosamine formation is a **proven protective mechanism**, not just a claim. *2 only* - This option is incorrect because it ignores statement 1, which accurately reflects **epidemiological evidence** linking high vitamin C intake with reduced cancer risk. - The association between dietary vitamin C and lower cancer incidence is **well-documented in observational studies**. *Neither 1 nor 2* - This option is completely incorrect as **both statements are scientifically accurate** and supported by substantial evidence. - Vitamin C's role in **cancer prevention through antioxidant activity and nitrosamine inhibition** is well-established in biochemistry and nutrition science.
Question 702: Consider the following statements regarding folic acid: 1. It is needed for normal development of blood cells in the marrow 2. It has a role in synthesis of nucleic acids 3. It is resistant to boiling Which of the above statements is/are correct?
- A. 1 and 2 (Correct Answer)
- B. 1 and 3
- C. 1 only
- D. 2 and 3
Explanation: ***1 and 2*** - **Folic acid** is a crucial coenzyme required for the synthesis of **purines** and **pyrimidines**, which are essential components of **DNA** and **RNA**. - This role in nucleic acid synthesis is vital for cell division and growth, explaining its necessity for the normal development of **blood cells** in the **bone marrow**. *1 and 3* - While folic acid is needed for normal blood cell development, it is generally **not resistant to boiling**. - Folic acid is quite **heat-sensitive** and its content can significantly decrease with cooking, especially prolonged boiling. *1 only* - Folic acid's role extends beyond just blood cell development; its involvement in nucleic acid synthesis is a fundamental biochemical function. - The synthesis of **DNA** and **RNA** is a primary reason why it's essential for rapidly dividing cells, like those in the bone marrow. *2 and 3* - Although folic acid plays a critical role in the synthesis of nucleic acids, it is **not resistant to boiling**. - Its heat-sensitive nature means that cooking methods can significantly impact the availability of **folic acid** in foods.
Question 703: Major source of vitamin K1 is:
- A. Fresh dark green vegetables (Correct Answer)
- B. Citrus fruits
- C. Exposure of body to sunlight
- D. Foods rich in polyunsaturated fatty acids
Explanation: ***Fresh dark green vegetables*** - **Phylloquinone (Vitamin K1)** is predominantly found in plants, particularly in **green leafy vegetables** such as kale, spinach, collard greens, and broccoli. - These vegetables are essential for providing the dietary form of vitamin K, which plays a crucial role in **blood clotting** and **bone metabolism**. *Citrus fruits* - Citrus fruits are well-known for being rich in **Vitamin C**, an essential antioxidant. - They are not a significant source of **Vitamin K1**. *Exposure of body to sunlight* - Exposure to sunlight is the primary natural mechanism for the body to synthesize **Vitamin D**. - Sunlight exposure does not contribute to the production or absorption of **Vitamin K**. *Foods rich in polyunsaturated fatty acids* - Foods rich in polyunsaturated fatty acids (PUFAs) include various vegetable oils, nuts, and fatty fish. - While important for overall health, PUFAs are not primary sources of **Vitamin K1**, although some oils may contain small amounts.
Question 704: Xanthurenic aciduria is seen in which vitamin deficiency?
- A. Vitamin B5
- B. Vitamin B12
- C. Vitamin B6 (Correct Answer)
- D. Vitamin B7
Explanation: ***Vitamin B6*** - **Xanthurenic aciduria** is a classic sign of **Vitamin B6 (pyridoxine) deficiency** because B6 is a crucial coenzyme for **kynureninase**, an enzyme in the **tryptophan metabolic pathway**. - Without sufficient B6, tryptophan cannot be properly metabolized, leading to the accumulation and excretion of xanthurenic acid. *Vitamin B5* - **Vitamin B5 (pantothenic acid)** is a precursor to **coenzyme A (CoA)**, essential for fatty acid metabolism and the **Krebs cycle**. - Its deficiency is associated with symptoms like paresthesia and fatigue, not xanthurenic aciduria. *Vitamin B12* - **Vitamin B12 (cobalamin)** is critical for DNA synthesis and the formation of **red blood cells**, and its deficiency causes **megaloblastic anemia** and neurological symptoms. - It plays no direct role in the tryptophan-kynurenine pathway, so its deficiency does not lead to xanthurenic aciduria. *Vitamin B7* - **Vitamin B7 (biotin)** acts as a coenzyme in **carboxylase reactions**, involved in fatty acid synthesis, gluconeogenesis, and amino acid metabolism. - Deficiency can cause dermatitis, hair loss, and neurological issues, but it is not linked to xanthurenic acid accumulation.
Question 705: Methyl-tetrahydrofolate (5-methyl-THF) gets accumulated in deficiency of which of the following?
- A. Vitamin B12 (Cobalamin) (Correct Answer)
- B. Vitamin B2 (Riboflavin)
- C. Vitamin B1 (Thiamine)
- D. Vitamin B6 (Pyridoxine)
Explanation: ***Vitamin B12 (Cobalamin)*** - A deficiency in **Vitamin B12** (cobalamin) leads to the accumulation of **5-methyl-tetrahydrofolate (5-methyl-THF)** due to the **"folate trap"** hypothesis. - This occurs because B12 is a cofactor for **methionine synthase**, which converts 5-methyl-THF back to tetrahydrofolate (THF), a necessary step for DNA synthesis and other one-carbon metabolism reactions. - Without B12, folate remains trapped in the methyl form and cannot be utilized for other essential reactions. *Vitamin B2 (Riboflavin)* - **Vitamin B2** (riboflavin) is a precursor for **FAD** and **FMN**, essential coenzymes in various redox reactions in the electron transport chain and other metabolic pathways. - Its deficiency typically presents as **cheilosis**, glossitis, and angular stomatitis, but does not cause methyl-THF accumulation. *Vitamin B1 (Thiamine)* - **Vitamin B1** (thiamine) is a cofactor for enzymes like **pyruvate dehydrogenase** and **alpha-ketoglutarate dehydrogenase** in carbohydrate metabolism. - Its deficiency causes **Beriberi** (wet, dry, or Wernicke-Korsakoff syndrome), affecting the cardiovascular and nervous systems, but does not affect folate metabolism. *Vitamin B6 (Pyridoxine)* - **Vitamin B6** (pyridoxine) is a coenzyme for many metabolic reactions, particularly in amino acid metabolism and neurotransmitter synthesis. - Deficiency can lead to **sideroblastic anemia**, neurological symptoms, and dermatitis, but does not cause methyl-THF accumulation.
Question 706: Most potent lipid phase antioxidant:
- A. Vitamin A
- B. Vitamin E (Correct Answer)
- C. Vitamin C
- D. Vitamin K
Explanation: ***Vitamin E*** - **Vitamin E** (primarily alpha-tocopherol) is a **fat-soluble antioxidant** that is highly effective at neutralizing **lipid peroxyl radicals** within cell membranes and lipoproteins, making it the most potent lipid-phase antioxidant. - It protects against **oxidative damage** to **polyunsaturated fatty acids** in lipid bilayers, which is crucial for maintaining cell membrane integrity. *Vitamin A* - **Vitamin A** (retinol and its derivatives) has antioxidant properties, particularly **beta-carotene**, which can scavenge **single oxygen radicals**. - However, its primary role is not as potent a lipid-phase chain-breaking antioxidant compared to vitamin E. *Vitamin C* - **Vitamin C** (ascorbic acid) is a **water-soluble antioxidant** that works primarily in aqueous environments, such as the cytosol and plasma. - It regenerates expended vitamin E by reducing the **tocopheroxyl radical**, but it doesn't directly act in the lipid phase. *Vitamin K* - **Vitamin K** is essential for **blood coagulation** and **bone metabolism**, serving as a cofactor for gamma-glutamyl carboxylase. - While it has some very limited antioxidant activity in specific contexts, it is not considered a significant or potent antioxidant, especially in the lipid phase.
Question 707: Which enzyme level is tested in thiamine deficiency?
- A. Transketolase (Correct Answer)
- B. PDH
- C. Kinase
- D. Pyruvate kinase
Explanation: ***Transketolase*** - The activity of **transketolase** in red blood cells is a reliable biochemical indicator of **thiamine deficiency (vitamin B1)**. - Thiamine pyrophosphate (TPP), the active form of thiamine, is a critical coenzyme for transketolase in the **pentose phosphate pathway**. *PDH* - **Pyruvate dehydrogenase (PDH)** is an enzyme complex that uses thiamine pyrophosphate as a cofactor, but its activity is not typically measured directly for diagnosing thiamine deficiency. - While PDH function is impaired in thiamine deficiency, direct assessment of transketolase activity is the standard diagnostic test. *Kinase* - **Kinase** is a general term for an enzyme that catalyzes the transfer of a phosphate group from a high-energy phosphate-donating molecule (like ATP) to a specific substrate. - This general class of enzymes is not specifically tested for thiamine deficiency. *Pyruvate kinase* - **Pyruvate kinase** is a key enzyme in **glycolysis** that catalyzes the final step of the pathway, converting phosphoenolpyruvate to pyruvate. - Its activity is not directly related to thiamine metabolism or deficiency.
Question 708: Wernicke's encephalopathy is due to deficiency of:
- A. B6
- B. Thiamine (Correct Answer)
- C. B12
- D. Niacin
Explanation: ***Thiamine*** - **Wernicke's encephalopathy** is a serious neurological disorder directly caused by a severe deficiency of **thiamine (vitamin B1)**. - Thiamine is crucial for **glucose metabolism** in the brain; its deficiency impairs energy production, leading to neuronal damage and the characteristic symptoms of confusion, ataxia, and ophthalmoplegia. *B6* - Deficiency of **vitamin B6 (pyridoxine)** can cause peripheral neuropathy, seizures, and microcytic anemia. - It is not the primary cause of the acute neurological syndrome seen in Wernicke's encephalopathy. *B12* - Deficiency of **vitamin B12 (cobalamin)** is associated with megaloblastic anemia and subacute combined degeneration of the spinal cord. - While it can cause neurological symptoms, they differ from the specific triad of Wernicke's encephalopathy. *Niacin* - Deficiency of **niacin (vitamin B3)** causes **pellagra**, characterized by dermatitis, diarrhea, and dementia. - Although it involves neurological symptoms (dementia), the presentation is distinct from Wernicke's encephalopathy.
Question 709: Wernicke-Korsakoff's syndrome is due to the deficiency of:
- A. Pyridoxine
- B. Riboflavin
- C. Thiamine (Correct Answer)
- D. Vitamin B12
Explanation: ***Correct: Thiamine*** - **Wernicke-Korsakoff syndrome** is a severe neurological disorder caused by a profound deficiency of **thiamine (vitamin B1)**, most commonly seen in chronic alcoholics - **Thiamine** is crucial for **glucose metabolism** in the brain, and its deficiency leads to impaired neuronal function and brain damage - **Wernicke encephalopathy** presents acutely with confusion, ataxia, and ophthalmoplegia - **Korsakoff psychosis** represents the chronic phase with profound memory impairment and confabulation *Incorrect: Pyridoxine* - Deficiency of **pyridoxine (vitamin B6)** can cause peripheral neuropathy, seizures, and sideroblastic anemia, but is not the cause of Wernicke-Korsakoff syndrome - **Isoniazid** treatment is a common cause of pyridoxine deficiency *Incorrect: Riboflavin* - **Riboflavin (vitamin B2)** deficiency leads to cheilosis, angular stomatitis, glossitis, and seborrheic dermatitis, but is not associated with Wernicke-Korsakoff syndrome - It plays a vital role as a coenzyme (FAD, FMN) in various **redox reactions** *Incorrect: Vitamin B12* - Deficiency of **vitamin B12 (cobalamin)** causes megaloblastic anemia and subacute combined degeneration of the spinal cord, with distinct neurological symptoms different from Wernicke-Korsakoff syndrome - **Intrinsic factor** is necessary for its absorption in the terminal ileum
Question 710: Vitamin K leads to?
- A. β-carboxylation of glutamic acid residues in clotting factors II, VII, IX, and X
- B. α-carboxylation of aspartic acid residues in clotting factors II, VII, IX, and X
- C. γ-carboxylation of aspartic acid residues in clotting factors II, VII, IX, and X
- D. γ-carboxylation of glutamic acid residues in clotting factors II, VII, IX, and X (Correct Answer)
Explanation: ***γ-carboxylation of glutamic acid residues in clotting factors II, VII, IX, and X*** - Vitamin K acts as a **cofactor** for the enzyme **γ-glutamyl carboxylase**, which is essential for the post-translational modification of specific clotting factors. - This modification involves adding a **carboxyl group** to the **gamma-carbon** of certain **glutamic acid residues** within coagulation factors II (prothrombin), VII, IX, and X, converting them to **γ-carboxyglutamic acid (Gla) residues**. - These Gla residues enable the clotting factors to bind **calcium ions**, which is critical for their activation and proper function in the coagulation cascade. *β-carboxylation of glutamic acid residues in clotting factors II, VII, IX, and X* - This option incorrectly states **beta-carboxylation**, whereas the correct process is **gamma-carboxylation**. - The specific carbon atom modified (gamma position) is crucial for the proper function of the clotting factors. *γ-carboxylation of aspartic acid residues in clotting factors II, VII, IX, and X* - This option incorrectly identifies the amino acid residue involved as **aspartic acid**. - Vitamin K-dependent carboxylation specifically modifies **glutamic acid residues**, not aspartic acid. *α-carboxylation of aspartic acid residues in clotting factors II, VII, IX, and X* - This option incorrectly specifies both the carbon position involved (**alpha-carboxylation**) and the amino acid residue (**aspartic acid**). - The correct process is **gamma-carboxylation** of **glutamic acid residues**.
Practice by Chapter
Fat-Soluble Vitamins: A, D, E, K
Practice Questions
Vitamin A and Vision
Practice Questions
Vitamin D and Calcium Metabolism
Practice Questions
Vitamin E and Antioxidant Functions
Practice Questions
Vitamin K and Blood Coagulation
Practice Questions
Water-Soluble Vitamins: B Complex and C
Practice Questions
Thiamine (B1) and Pyruvate Dehydrogenase
Practice Questions
Riboflavin (B2) and Flavin Coenzymes
Practice Questions
Niacin and NAD/NADP
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Vitamin B6 and Transamination
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Folate and Vitamin B12 in One-Carbon Metabolism
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Vitamin C and Collagen Synthesis
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