Vitamins and Coenzymes — MCQs

Vitamins and Coenzymes Indian Medical PG Practice Questions and MCQs

Question 761: Which of the following is not a good source of vitamin C?

A. Amla
B. Lime
C. Guava
D. Egg (Correct Answer)

Explanation: ***Egg*** - Eggs are a good source of **protein**, **choline**, **vitamins B12 and D**, but contain **negligible amounts of vitamin C**. - Vitamin C is primarily found in **fruits and vegetables**. *Amla* - **Amla** (Indian gooseberry) is an exceptionally rich source of **vitamin C**, often used in traditional medicine for its high content. - It contains significantly more vitamin C than many other fruits, making it a powerful antioxidant. *Lime* - **Lime**, like other citrus fruits, is an excellent source of **vitamin C**, contributing to immune function and collagen synthesis. - A single lime can provide a substantial portion of the recommended daily intake of vitamin C. *Guava* - **Guava** is remarkably rich in **vitamin C**, often containing several times the amount found in oranges. - It also provides fiber and other antioxidants, making it a highly nutritious fruit.

Question 762: 1,25-dihydroxyvitamin D3 (calcitriol) acts on?

A. Cytosolic receptors
B. Surface receptors
C. Nuclear receptors (Correct Answer)
D. None of the above

Explanation: ***Nuclear receptors*** - **Calcitriol** (1,25-dihydroxyvitamin D3), being a steroid hormone derivative, is **lipid-soluble** and readily crosses the cell membrane. - It binds to specific **Vitamin D Receptors (VDRs)**, which belong to the **nuclear receptor superfamily**. - VDRs may initially be located in the cytoplasm, but upon ligand binding, they translocate to the nucleus where they bind to DNA and regulate gene transcription. - The classification as "nuclear receptors" refers to their **functional site of action** (the nucleus), not necessarily their initial cellular location. *Cytosolic receptors* - While VDRs can be found in the cytoplasm before activation, they are **not classified as "cytosolic receptors"** in standard biochemistry terminology. - The correct classification is **nuclear receptors**, which distinguishes them from membrane receptors and reflects their primary mechanism of gene regulation in the nucleus. *Surface receptors* - **Surface (membrane) receptors** mediate the effects of **water-soluble hormones** like peptide hormones and catecholamines that cannot cross the lipid bilayer. - Calcitriol's **lipid-soluble nature** allows it to enter cells directly and act through intracellular nuclear receptors, not membrane-bound receptors. *None of the above* - This option is incorrect because calcitriol definitively acts through **nuclear receptors** (VDRs) to exert its physiological effects on calcium homeostasis and gene expression. - This mechanism is well-established in biochemistry and endocrinology.

Question 763: Which vitamin is most directly involved in promoting wound healing?

A. Vitamin C (Correct Answer)
B. Vitamin D
C. Vitamin A
D. Niacin

Explanation: ***Vitamin C*** - Vitamin C is essential for **collagen synthesis**, a crucial protein for the structural integrity of new tissue in wound healing. - It acts as a cofactor for **prolyl and lysyl hydroxylase enzymes**, which are required for the hydroxylation of proline and lysine residues in collagen—this is the most direct biochemical mechanism in wound healing. - It also acts as an important **antioxidant** that protects cells from damage during the inflammatory phase of wound repair. *Vitamin D* - Vitamin D is primarily involved in **calcium and phosphate homeostasis** and bone health. - While it has immunomodulatory roles and can influence wound healing indirectly, its direct involvement in the **collagen synthesis pathway** specific to wound healing is not as prominent as Vitamin C. *Vitamin A* - Vitamin A is important for **epithelial cell differentiation**, collagen synthesis, and immune function in wound healing. - It plays a significant role in **epithelialization** and can reverse steroid-induced healing defects. - However, its mechanism is broader and less direct than Vitamin C's specific role as a **cofactor in collagen hydroxylation**, which is why Vitamin C is considered most directly involved. *Niacin* - Niacin (Vitamin B3) is involved in **metabolic processes** as a component of coenzymes NAD and NADP. - It plays a role in cellular energy production but does not have a direct, primary role in promoting wound healing through collagen synthesis like Vitamin C.

Question 764: What is the primary function of Vitamin C in the human body?

A. Synthesis of neurotransmitters
B. Antioxidant function
C. Collagen synthesis (Correct Answer)
D. All of the options

Explanation: ***Collagen synthesis*** - Vitamin C is an essential cofactor for **prolyl hydroxylase** and **lysyl hydroxylase**, enzymes critical for the **hydroxylation of proline and lysine residues** in procollagen - This hydroxylation is vital for the proper **cross-linking and stability of collagen fibers**, which are crucial for connective tissues, skin, bones, and blood vessels - **Deficiency causes scurvy**, directly demonstrating its critical importance in maintaining structural integrity *Synthesis of neurotransmitters* - Vitamin C is involved in neurotransmitter synthesis, particularly as a cofactor for **dopamine β-hydroxylase**, which converts dopamine to norepinephrine - While important, this is not considered its *primary* function given the widespread impact of collagen throughout the body *Antioxidant function* - Vitamin C is a potent **water-soluble antioxidant** that protects cells from damage by free radicals and reactive oxygen species - This is a significant secondary role, but structural integrity and healing processes rely more fundamentally on collagen synthesis *All of the options* - Although Vitamin C performs all the listed functions, the question specifically asks for the *primary* function - **Collagen synthesis** is universally recognized as its most vital role, as evidenced by the severe consequences of deficiency (scurvy with bleeding gums, poor wound healing, and connective tissue breakdown) - The other functions, while physiologically important, are secondary compared to maintaining **connective tissue integrity**

Question 765: A young patient started to take a weight loss medication that acts by inhibiting fat absorption from food. After a few weeks, she developed easy bruising and increased menstrual bleeding. Deficiency of which of the following vitamins is responsible for her condition?

A. Vitamin E
B. Vitamin K (Correct Answer)
C. Vitamin B6
D. Vitamin D

Explanation: ***Vitamin K*** - The patient is taking a **weight-loss medication** that **inhibits fat absorption**, leading to a deficiency in **fat-soluble vitamins**, including vitamin K. - **Vitamin K** is crucial for the synthesis of **coagulation factors** (II, VII, IX, X), and its deficiency leads to impaired clotting, manifesting as **easy bruising** and **increased menstrual bleeding**. *Vitamin E* - While vitamin E is a fat-soluble vitamin, its deficiency typically causes **neurological dysfunction** and **hemolytic anemia**, not bleeding diathesis. - Although malabsorption of vitamin E can occur with fat malabsorption, it does not directly explain the bleeding symptoms observed. *Vitamin B6* - Vitamin B6 is a **water-soluble vitamin**, so its absorption would not be directly affected by a medication inhibiting fat absorption. - Its deficiency can cause **neuropathy**, **dermatitis**, and **anemia**, but not increased bleeding. *Vitamin D* - Vitamin D is a **fat-soluble vitamin** whose deficiency is associated with **bone disorders** like **osteomalacia** and **rickets**, not bleeding. - While its absorption would be impacted by the medication, its deficiency would not cause easy bruising or increased menstrual bleeding.

Question 766: A family consumes only polished rice. Which of the following combinations of vitamin deficiency and enzymatic defect will be present in this family?

A. Thiamine-transketolase (Correct Answer)
B. Riboflavin-glutathione reductase
C. Thiamine-transaminase
D. Riboflavin-transketolase

Explanation: ***Thiamine-transketolase*** - Consumption of **polished rice** is a classic cause of **thiamine (vitamin B1) deficiency** because the polishing process removes the outer layers of the grain where thiamine is abundant. - **Transketolase** is a key enzyme in the **pentose phosphate pathway** that requires thiamine pyrophosphate (TPP) as a cofactor, making its activity a reliable indicator of thiamine status. *Riboflavin-glutathione reductase* - **Glutathione reductase** activity is indeed used to assess **riboflavin (vitamin B2) status**, as it requires FAD (a derivative of riboflavin) as a cofactor. - However, **riboflavin deficiency** is not characteristically associated with consumption of polished rice. *Thiamine-transaminase* - While this option correctly identifies **thiamine**, the associated enzyme, **transaminase**, is incorrect in this context. - **Transaminases** are primarily dependent on **pyridoxal phosphate (vitamin B6)** as a cofactor, not thiamine. *Riboflavin-transketolase* - This option incorrectly combines **riboflavin deficiency** with the enzyme **transketolase**. - As mentioned, **transketolase** activity is specifically used to assess **thiamine status**, not riboflavin status.

Question 767: A patient presenting with bleeding gums and easy bruisability was diagnosed with scurvy. This condition results from a deficiency of which of the following?

A. Inhibition of vitamin K
B. Increased collagen breakdown
C. Defective collagen synthesis
D. Low vitamin C (Correct Answer)

Explanation: ***Low vitamin C*** - **Scurvy** is directly caused by a severe deficiency of **vitamin C (ascorbic acid)**. - Vitamin C is a cofactor for **prolyl hydroxylase** and **lysyl hydroxylase**, enzymes essential for **collagen synthesis**. - Its deficiency leads to defective collagen formation, resulting in weakened connective tissues and fragile capillaries, explaining the bleeding gums and easy bruising. *Inhibition of vitamin K* - **Vitamin K** is crucial for the synthesis of **blood clotting factors** (II, VII, IX, X). - Its inhibition (e.g., by warfarin) would lead to bleeding disorders but does not explain the characteristic connective tissue problems (poor wound healing, perifollicular hemorrhages) seen in scurvy. *Increased collagen breakdown* - Conditions like **Ehlers-Danlos syndrome** involve abnormal collagen structure leading to tissue fragility. - Scurvy is characterized by a problem in the *synthesis* rather than the increased *breakdown* of collagen. *Defective collagen synthesis* - While this describes the **pathophysiological mechanism** of scurvy, it is not the answer to what the patient is *deficient in*. - The question asks for the underlying **nutritional deficiency**, which is **vitamin C**—the root cause that leads to defective collagen synthesis.

Question 768: Which of the following is the richest source of vitamin B12?

A. Meat (Correct Answer)
B. Green leafy vegetables
C. Corn oil
D. Sunflower oil

Explanation: ***Meat*** - **Meat** and other animal products are the primary natural dietary sources of **vitamin B12** (cobalamin). - This is because vitamin B12 is synthesized by bacteria and accumulates in animal tissues. *Green leafy vegetables* - **Green leafy vegetables** are excellent sources of many vitamins and minerals, such as **folate** and **vitamin K**, but they do not contain vitamin B12. - Vitamin B12 is essentially absent in plant-based foods unless they are fortified or contaminated. *Corn oil* - **Corn oil** is a vegetable oil primarily composed of fats and is a source of **vitamin E** and fatty acids, but it does not contain vitamin B12. - Oils derived from plants lack intrinsic vitamin B12 content. *Sunflower oil* - Similar to corn oil, **sunflower oil** is a plant-based oil rich in **vitamin E** and unsaturated fatty acids, but it contains **no vitamin B12**. - Plant oils are not a source of vitamin B12, which is almost exclusively found in animal products.

Question 769: Which vitamin deficiency is associated with night blindness?

A. Biotin
B. Vit. A (Correct Answer)
C. Thiamine
D. Riboflavin

Explanation: ***Vitamin A*** - **Vitamin A deficiency is THE classic cause of night blindness (nyctalopia)**, one of the earliest signs of deficiency - Vitamin A is essential for synthesis of **rhodopsin**, the photopigment in retinal rod cells responsible for vision in dim light - Deficiency leads to impaired dark adaptation and progressive loss of night vision - Other manifestations include **xerophthalmia, Bitot's spots, and keratomalacia** - This is a high-yield fact for NEET-PG examinations *Riboflavin (Vitamin B2)* - Riboflavin deficiency causes **oral-ocular-genital syndrome** - Clinical features include **angular stomatitis, cheilosis, glossitis, seborrheic dermatitis** - Eye manifestations include **corneal vascularization and photophobia**, NOT night blindness - Does NOT cause night blindness as a primary symptom *Thiamine (Vitamin B1)* - Thiamine deficiency causes **Beriberi** (wet and dry forms) and **Wernicke-Korsakoff syndrome** - Characterized by peripheral neuropathy, cardiac dysfunction, and CNS manifestations - Does NOT cause night blindness *Biotin (Vitamin B7)* - Biotin deficiency is rare and causes **dermatitis, alopecia, conjunctivitis** - Also causes neurological symptoms in severe deficiency - Does NOT cause night blindness

Question 770: Which of the following is NOT a manifestation of vitamin E deficiency?

A. Posterior column abnormalities
B. Cerebellar ataxia
C. Hemolytic anemia
D. Autonomic dysfunction (Correct Answer)

Explanation: ***Autonomic dysfunction*** - **Autonomic dysfunction** is not typically associated with vitamin E deficiency. Instead, it is commonly seen in conditions like **diabetes mellitus**, Parkinson's disease, or certain inherited neuropathies. - Vitamin E primarily acts as an **antioxidant** and is crucial for neurological and red blood cell health. *Hemolytic anemia* - Vitamin E is an **antioxidant** that protects red blood cell membranes from **oxidative damage**. - Its deficiency can lead to increased fragility and **hemolysis** of red blood cells, resulting in hemolytic anemia, particularly in premature infants. *Posterior column abnormalities* - Vitamin E deficiency can cause **neurological dysfunction** due to oxidative damage to neuronal membranes. - This often manifests as degeneration of the **posterior columns** of the spinal cord, leading to impaired proprioception and vibratory sensation. *Cerebellar ataxia* - The **cerebellum** is highly susceptible to oxidative stress, and vitamin E deficiency can lead to damage in this area. - This damage results in **ataxia**, characterized by impaired coordination, balance, and gait disturbances.

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

Practice Questions

Vitamin B6 and Transamination

Practice Questions

Folate and Vitamin B12 in One-Carbon Metabolism

Practice Questions

Vitamin C and Collagen Synthesis

Practice Questions

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