Vitamins and Coenzymes Practice Questions

Q: All of the following are water-soluble antioxidants except?

Carotenes. ***Carotenes*** - **Carotenes** are **lipid-soluble** antioxidants that are typically found in cell membranes and lipid components of the body. - They protect against **lipid peroxidation**, which is damage to cellular membranes caused by free radicals. *Ascorbate* - **Ascorbate** (Vitamin C) is a well-known **water-soluble** antioxidant that readily donates electrons to neutralize free radicals in aqueous environments. - It plays a crucial role in regenerating other antioxidants, such as **alpha-tocopherol (Vitamin E)**. *Uric acid* - **Uric acid** is a potent **water-soluble** antioxidant present in high concentrations in the plasma. - It scavenges various reactive oxygen species and reactive nitrogen species, especially in the **extracellular fluid**. *Polyphenols* - **Polyphenols** are a large group of **water-soluble** compounds found in plants that act as antioxidants. - They reduce oxidative stress by **scavenging free radicals**, chelating metal ions, and inhibiting enzymes involved in radical generation.

Q: A common finding in osteomalacia is

Low serum calcium. ***Low serum calcium*** - **Osteomalacia** is characterized by defective **bone mineralization**, often due to vitamin D deficiency, which leads to impaired calcium absorption and subsequent **hypocalcemia** [1]. - To compensate for low serum calcium, **parathyroid hormone (PTH)** levels increase, further contributing to altered bone metabolism [1]. *Low serum phosphate* - While osteomalacia often features **hypophosphatemia**, it is not always the primary or most consistent finding, as **calcium** dysregulation is central to the disease [1]. - **Secondary hyperparathyroidism** in some cases of osteomalacia can lead to increased phosphate excretion, causing low phosphate, but **hypocalcemia** is more directly related to the mineralization defect [1]. *Normal level of 1, 25 di-hydroxy vit D3* - **1,25-dihydroxyvitami n D3** (calcitriol) levels are typically **low** in nutritional osteomalacia, as this is the active form crucial for calcium absorption and bone mineralization [1]. - Normal levels would contradict the underlying pathology of vitamin D deficiency that causes the condition. *Normal hydroxy proline levels in urine* - **Hydroxyproline** is an amino acid found in collagen, and its urinary excretion reflects **bone turnover**; in osteomalacia, due to defective mineralization and sometimes increased bone resorption, hydroxyproline levels can be elevated or altered. - Normal levels would not be expected given the significant bone metabolic disturbances in osteomalacia.

Q: A boy who refuses to eat fruit presents with knee swelling and hematoma. Which vitamin deficiency is most likely suspected?

Vitamin C. ***Vitamin C*** - A refusal to eat fruit, a primary source of **vitamin C**, is a significant risk factor for deficiency. - **Vitamin C** deficiency (scurvy) impairs **collagen synthesis**, leading to fragile capillaries, easy bruising (**hematoma**), and poor wound healing, which can manifest as **joint swelling**. *Vitamin D* - Deficiency typically causes **rickets** in children, characterized by **bone deformities**, bowing of the legs, and impaired growth. - It does not directly cause **hematomas** or acute **joint swelling** from capillary fragility. *Vitamin E* - Deficiency is rare and usually associated with **fat malabsorption disorders**. - It can lead to **neurological symptoms** like ataxia and peripheral neuropathy, not typically **hematomas** or **joint swelling**. *Vitamin B1* - Deficiency (beriberi) affects the **cardiovascular** and **nervous systems**, causing symptoms like heart failure, peripheral neuropathy, and muscle weakness. - It does not cause **hematomas** or **joint swelling** as primary manifestations.

Q: Which vitamin is required for transfer of 1-carbon unit?

Folic acid. ***Folic acid*** - **Folic acid** (vitamin B9) is essential for the transfer of **one-carbon units**, particularly as **tetrahydrofolate (THF)**. - These one-carbon units are critical in metabolic processes such as **DNA synthesis**, **amino acid metabolism**, and **neurotransmitter synthesis**. *Vitamin A* - **Vitamin A** (retinol) is primarily involved in **vision**, **immune function**, and **cell differentiation**. - It does not play a direct role in the transfer of one-carbon units. *Vitamin B12* - **Vitamin B12** (cobalamin) is involved in two main reactions: the conversion of **methylmalonyl-CoA to succinyl-CoA** and the transfer of a **methyl group from N5-methyl THF to homocysteine** to form methionine. - While it works with folate, it does not directly transfer one-carbon units in the same way as folic acid. *Niacin* - **Niacin** (vitamin B3) is a precursor to **NAD+ and NADP+**, which are crucial coenzymes in **redox reactions** and energy metabolism. - It is not involved in the transfer of one-carbon units.

Q: Macrocytic anaemia is due to a deficiency of:

Vitamin B12. ***Vitamin B12*** - A deficiency in **Vitamin B12** (cobalamin) impairs DNA synthesis, leading to **megaloblastic erythropoiesis** where red blood cells are larger than normal [1]. - This results in **macrocytic anemia**, characterized by an elevated **mean corpuscular volume (MCV)** [1]. *Vitamin B1* - A deficiency in **Vitamin B1** (thiamine) primarily causes **Beriberi**, affecting the nervous and cardiovascular systems. - It is not directly associated with the development of **macrocytic anemia**. *Vitamin B2* - A deficiency in **Vitamin B2** (riboflavin) can cause **normocytic, normochromic anemia**, but not typically macrocytic anemia. - It also presents with symptoms like **cheilosis**, **glossitis**, and **seborrheic dermatitis**. *Vitamin B6* - A deficiency in **Vitamin B6** (pyridoxine) can lead to **sideroblastic anemia**, which is typically **microcytic** and **hypochromic**, not macrocytic [2]. - It impairs heme synthesis, causing iron accumulation in red blood cell precursors.

Q: Anti-infective vitamin is

Vitamin A. ***Vitamin A*** - Vitamin A is known as the **anti-infective vitamin** because it plays a crucial role in maintaining the integrity of **epithelial tissues**, which serve as the body's first line of defense against pathogens. - It also supports the proper functioning of the **immune system**, including the development and differentiation of lymphocytes and other immune cells. *Vitamin B6* - Vitamin B6 (pyridoxine) is essential for numerous **metabolic functions**, including amino acid, carbohydrate, and fat metabolism. - While it contributes to overall health, it is not primarily known as an anti-infective vitamin in the same way as Vitamin A. *Vitamin D* - Vitamin D is primarily associated with **bone health** due to its role in calcium and phosphate regulation. - It also has immunomodulatory effects, but its primary function is not anti-infective protection of epithelial barriers. *Vitamin C* - Vitamin C (ascorbic acid) is a powerful **antioxidant** and plays a vital role in **collagen synthesis** and immune function. - While important for immunity, its primary role is not maintaining epithelial integrity against infection to the extent of Vitamin A.

Q: Which dietary deficiency of a vitamin can cause pellagra?

Niacin. ***Niacin*** - **Pellagra** is classically described by the "4 D's": **dermatitis**, **diarrhea**, **dementia**, and eventually **death**, all of which are caused by a deficiency in **niacin (Vitamin B3)**. - Niacin is crucial for energy metabolism and DNA repair, and its deficiency affects rapidly dividing cells, especially in the skin, gastrointestinal tract, and nervous system. *Vitamin A* - Deficiency in **Vitamin A** primarily leads to **vision problems**, including **night blindness** and, in severe cases, **xerophthalmia** and irreversible blindness. - While it can impact immune function and epithelial integrity, it does not cause the characteristic triad of pellagra. *Folate* - A deficiency in **folate (Vitamin B9)** is primarily associated with **megaloblastic anemia**, which involves enlarged, immature red blood cells. - It does not cause the dermatological, gastrointestinal, or neurological symptoms seen in pellagra. *Vitamin B12* - **Vitamin B12 (cobalamin) deficiency** also causes **megaloblastic anemia**, but it is uniquely associated with **neurological symptoms** such as peripheral neuropathy, cognitive impairment, and subacute combined degeneration of the spinal cord. - While there is some neurological overlap, its clinical presentation is distinct from pellagra and does not involve the characteristic dermatitis or severe diarrhea.

Q: A 5-year-old female patient complains of a deformed shape of her legs. The patient is a strict vegetarian, and laboratory investigations reveal elevated levels of alkaline phosphatase. This patient may be suffering from a deficiency of:

Vitamin D. ***Vitamin D*** - **Vitamin D deficiency** in children leads to **rickets**, characterized by defective bone mineralization causing softened and weakened bones, resulting in **deformed legs** (e.g., bowed legs). - **Elevated alkaline phosphatase** is a common laboratory finding in rickets and osteomalacia, reflecting increased osteoblast activity attempting to mineralize uncalcified bone matrix. *Vitamin A* - **Vitamin A deficiency** can lead to **night blindness**, xerophthalmia, and impaired immune function, but not directly to bone deformities. - It plays a crucial role in vision, immune system function, and cell growth, not bone calcification. *Vitamin B1* - **Vitamin B1 (thiamine) deficiency** causes **beriberi**, affecting the cardiovascular (wet beriberi) and nervous systems (dry beriberi). - Symptoms include heart failure, peripheral neuropathy, and Wernicke-Korsakoff syndrome, which are unrelated to bone deformities. *Vitamin C* - **Vitamin C (ascorbic acid) deficiency** results in **scurvy**, characterized by impaired collagen synthesis. - Clinical signs include bleeding gums, petechiae, poor wound healing, and joint pain, but not primary bone deformities like bowed legs.

Q: Gamma-glutamyl carboxypeptidase is linked with the absorption of which vitamin?

Folic acid. ***Folic acid*** - **Gamma-glutamyl carboxypeptidase**, also known as **folylpolyglutamate hydrolase** or **conjugase**, is an enzyme crucial for the absorption of dietary folic acid. - It hydrolyzes the polyglutamyl forms of folate found in food into **monoglutamyl folate**, which can then be absorbed in the small intestine. *Riboflavin* - **Riboflavin (vitamin B2)** absorption does not directly involve gamma-glutamyl carboxypeptidase. - Its absorption primarily relies on **active transport mechanisms** and facilitated diffusion in the small intestine. *Niacin* - **Niacin (vitamin B3)** absorption is mainly through **passive diffusion** and, at lower concentrations, by carrier-mediated transport. - It is not dependent on the enzymatic activity of gamma-glutamyl carboxypeptidase. *Pyridoxine* - **Pyridoxine (vitamin B6)** is absorbed mainly by **passive diffusion** in the jejunum. - Its absorption does not involve gamma-glutamyl carboxypeptidase.

Q: What is the form of folate that accumulates in vitamin B12 deficiency due to the inhibition of methionine synthase?

Methyl-THFA. ***Methyl-THFA*** - In **vitamin B12 deficiency**, the enzyme **methionine synthase** is inhibited, as it requires B12 as a cofactor. - This leads to the accumulation of **methyl-THFA (5-methyltetrahydrofolate)** because it cannot be converted back to tetrahydrofolate (THF), trapping it in this form—known as the "**methyl-trap hypothesis**." *Formyl THFA* - **Formyl THFA (10-formyltetrahydrofolate)** is a folate derivative involved in purine synthesis, not directly accumulated due to B12 deficiency. - Its levels are not specifically noted to increase in the context of methionine synthase inhibition. *Methylene-THFA* - **Methylene-THFA (5,10-methylenetetrahydrofolate)** is an important substrate for **thymidylate synthase** in DNA synthesis. - While its metabolism is linked to folate, it does not accumulate as the primary "methyl-trap" form in B12 deficiency. *Methenyl THFA* - **Methenyl THFA (5,10-methenyltetrahydrofolate)** is an intermediate in folate metabolism, interconverting with methylene-THFA and formyl-THFA. - Like other folate derivatives not directly involved in the inhibited methionine synthase step, it doesn't accumulate specifically in B12 deficiency.

Question 1

All of the following are water-soluble antioxidants except?

Accepted Answer

Carotenes

Answer

uric acid

Answer

Polyphenols

Answer

Ascorbate

Question 2

A common finding in osteomalacia is

Accepted Answer

Low serum calcium

Answer

Low serum phosphate

Answer

Normal hydroxy proline levels in urine

Answer

Normal level of 1, 25 di-hydroxy vit D3

Question 3

A boy who refuses to eat fruit presents with knee swelling and hematoma. Which vitamin deficiency is most likely suspected?

Accepted Answer

Vitamin C

Answer

Vitamin D

Answer

Vitamin E

Answer

Vitamin B1

Question 4

Which vitamin is required for transfer of 1-carbon unit?

Accepted Answer

Folic acid

Answer

Niacin

Answer

Vitamin B12

Answer

Vitamin A

Question 5

Macrocytic anaemia is due to a deficiency of:

Accepted Answer

Vitamin B12

Answer

Vitamin B1

Answer

Vitamin B2

Answer

Vitamin B6

Question 6

Anti-infective vitamin is

Accepted Answer

Vitamin A

Answer

Vitamin D

Answer

Vitamin C

Answer

Vitamin B6

Question 7

Which dietary deficiency of a vitamin can cause pellagra?

Accepted Answer

Niacin

Answer

Vitamin A

Answer

Folate

Answer

Vitamin B12

Question 8

A 5-year-old female patient complains of a deformed shape of her legs. The patient is a strict vegetarian, and laboratory investigations reveal elevated levels of alkaline phosphatase. This patient may be suffering from a deficiency of:

Accepted Answer

Vitamin D

Answer

Vitamin A

Answer

Vitamin B1

Answer

Vitamin C

Question 9

Gamma-glutamyl carboxypeptidase is linked with the absorption of which vitamin?

Accepted Answer

Folic acid

Answer

Riboflavin

Answer

Niacin

Answer

Pyridoxine

Question 10

What is the form of folate that accumulates in vitamin B12 deficiency due to the inhibition of methionine synthase?

Accepted Answer

Methyl-THFA

Answer

Formyl THFA

Answer

Methylene-THFA

Answer

Methenyl THFA

Vitamins and Coenzymes — MCQs

Vitamins and Coenzymes — MCQs

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