Vitamins and Coenzymes Practice Questions

Q: Active form of Vitamin D is:

Calcitriol. ***Calcitriol*** - **Calcitriol** (1,25-dihydroxycholecalciferol) is the **biologically active form of vitamin D**. - It is produced primarily in the kidneys from calcifediol and is responsible for regulating **calcium and phosphate levels** in the body. *Calcifediol* - **Calcifediol** (25-hydroxyvitamin D) is the main circulating form of vitamin D, produced in the liver from cholecalciferol. - It is **not the active form**; rather, it is a precursor that needs further hydroxylation in the kidneys to become calcitriol. *Paricalcitol* - **Paricalcitol** is a **synthetic vitamin D analog** used therapeutically to prevent and treat secondary hyperparathyroidism. - It is not the naturally occurring active form of vitamin D in the body. *Cholecalciferol* - **Cholecalciferol** (vitamin D3) is the form of vitamin D synthesized in the skin upon exposure to sunlight or obtained from the diet. - It is a **precursor** to the active form and requires two hydroxylation steps (in the liver and kidneys) to become calcitriol.

Q: Glutathione reductase assay is helpful in assessing the deficiency of

Riboflavin. ***Riboflavin*** - The **glutathione reductase assay** measures the activity of the enzyme glutathione reductase, which uses **FAD** (derived from riboflavin) as a coenzyme. - A significant increase in enzyme activity upon addition of FAD indicates **riboflavin deficiency**, as the enzyme was previously operating at suboptimal levels due to insufficient FAD. *Niacin* - Niacin is a precursor for **NAD+** and **NADP+**, which are involved in many redox reactions, but not directly as a coenzyme for glutathione reductase. - Deficiency leads to **pellagra**, characterized by dermatitis, diarrhea, and dementia. *Pyridoxine* - Pyridoxine (vitamin B6) is a precursor for **pyridoxal phosphate (PLP)**, a coenzyme involved in amino acid metabolism. - It is not directly linked to the function of glutathione reductase. *Vit B5* - Vitamin B5 (pantothenic acid) is a component of **coenzyme A (CoA)**, crucial for fatty acid synthesis and degradation, and the citric acid cycle. - It does not directly affect the activity of glutathione reductase.

Q: All are true regarding vitamin D, except ?

1-hydroxylation in liver. ***1-hydroxylation in liver*** - The **1-alpha-hydroxylation** of 25-hydroxyvitamin D (calcidiol) primarily occurs in the **kidneys** to form the active form, **calcitriol (1,25-dihydroxyvitamin D)**. - The liver is responsible for the **25-hydroxylation** of vitamin D to calcidiol, not the 1-hydroxylation step. *Sunlight is important* - Exposure to **ultraviolet B (UVB) rays** from sunlight is crucial for the endogenous synthesis of **vitamin D3 (cholecalciferol)** in the skin from 7-dehydrocholesterol. - Insufficient sun exposure can lead to **vitamin D deficiency**, especially in individuals with darker skin or those living at higher latitudes. *Active form is calcitriol* - **Calcitriol (1,25-dihydroxyvitamin D)** is the hormonally active form of vitamin D, playing a key role in **calcium and phosphate homeostasis**. - It acts on target tissues like the intestine, bone, and kidney to regulate mineral metabolism. *RDA for children is 400 IU* - The recommended dietary allowance (RDA) for **infants and children** is typically **400 International Units (IU)** of vitamin D per day. - This recommendation helps prevent **rickets** in children and supports healthy bone development.

Q: During the dark phase of visual cycle, which form of vitamin A combines with opsin to make Rhodopsin:

11-cis-Retinaldehyde. ***11-cis-Retinaldehyde*** - In the **dark phase** of the visual cycle, **11-cis-retinaldehyde** (retinal) is regenerated and combines with **opsin** to form **rhodopsin**. - This molecule is crucial for initiating the visual transduction pathway in **rod cells** when light is detected. *11-cis-Retinol* - **11-cis-Retinol** is an intermediate in the regeneration of 11-cis-retinaldehyde from all-trans-retinol, but it does not directly bind to opsin to form rhodopsin. - It is converted to 11-cis-retinaldehyde by the enzyme **11-cis-retinol dehydrogenase**. *all trans-Retinol* - **All-trans-retinol** is the form of vitamin A transported to the eye and is also an intermediate in the visual cycle, but it does not combine directly with opsin. - It is converted to all-trans-retinaldehyde after the absorption of light and then subsequently isomerized to 11-cis-retinol. *All trans-Retinaldehyde* - **All-trans-retinaldehyde** is formed when **rhodopsin** absorbs light, causing the isomerization of 11-cis-retinaldehyde. - This molecule is then released from opsin and subsequently reduced to all-trans-retinol before being recycled back to 11-cis-retinaldehyde in the pigment epithelium.

Q: All of the following statements are true except:

25(OH)D3 is the most active form of vitamin D. ***25(OH)D3 is the most active form of vitamin D*** - This statement is incorrect. While **25(OH)D3 (calcifediol)** is the major circulating form of vitamin D, it is not the most active form. - The most active form of vitamin D is **1,25(OH)2D3 (calcitriol)**, which is formed by the 1-alpha hydroxylation of calcifediol in the kidneys. *25–α hydroxylation takes place in liver* - This statement is true. The initial hydroxylation of **vitamin D3 (cholecalciferol)** at the 25-position occurs in the liver, forming 25(OH)D3 (calcifediol). - This step is catalyzed by the enzyme **25-hydroxylase**. *1–α hydroxylation takes place in kidney* - This statement is true. The 25(OH)D3 produced in the liver is then transported to the kidneys, where it undergoes a second hydroxylation at the 1-alpha position. - This step, catalyzed by **1-alpha-hydroxylase**, forms the biologically active hormone 1,25(OH)2D3 (calcitriol). *Daily requirement in the absence of sun–light is 450-600 IU/day* - This statement is generally true. The recommended daily allowance (RDA) for vitamin D in adults, especially in the absence of sufficient sun exposure, typically ranges from **400 to 800 IU (international units)**, with 600 IU/day being a common guideline. - This requirement can vary based on age, geographical location, and other individual factors.

Q: Which of the following cause low serum calcium?

Vit D deficiency. ***Vit D deficiency*** - **Vitamin D** is crucial for **intestinal absorption of calcium**; its deficiency leads to reduced calcium uptake from the diet. - Low vitamin D levels stimulate **parathyroid hormone (PTH) release**, which initially maintains serum calcium by bone resorption, but chronic deficiency eventually results in **hypocalcemia**. - In the context of nutritional causes of hypocalcemia, **Vitamin D deficiency** is the **most common dietary/nutritional cause** tested in biochemistry. *GH* - **Growth hormone (GH)** primarily influences **bone growth** and protein synthesis, but is not directly responsible for regulating serum calcium levels. - While GH can indirectly affect calcium metabolism through IGF-1, it does **not cause hypocalcemia**. *Hypoparathyroidism* - **Hypoparathyroidism** is characterized by **insufficient parathyroid hormone (PTH)** production, leading to **low serum calcium**. - Without adequate PTH, **calcium reabsorption** from bones and kidneys is impaired, and **vitamin D activation** is reduced, resulting in hypocalcemia. - **Note**: While hypoparathyroidism does cause hypocalcemia, in a **biochemistry/nutrition context**, Vitamin D deficiency is the focus as a nutritional/metabolic cause, whereas hypoparathyroidism is more of an endocrine disorder. *Glucocorticoids* - **Glucocorticoids**, particularly at high doses and with long-term use, **reduce intestinal calcium absorption** and increase **bone resorption**. - Despite their impact on bone, they typically cause **hypercalciuria** (increased urinary calcium excretion) and can lead to **osteoporosis**, but do not directly cause **hypocalcemia** due to compensatory mechanisms.

Q: Osteomalacia is due to -

Vitamin D deficiency. ***Vitamin D deficiency*** - **Osteomalacia** is characterized by defective **bone mineralization** in adults, primarily due to insufficient **calcium** and **phosphate** availability for deposition into the bone matrix [1]. - The most common cause of impaired mineralization is severe and prolonged **vitamin D deficiency**, which leads to reduced absorption of calcium and phosphate from the gut [1]. [2]. *Vitamin E deficiency* - **Vitamin E** is an important **antioxidant** that protects cells from damage, but its deficiency is not directly linked to osteomalacia. - Deficiency can lead to **neurological symptoms** like ataxia, peripheral neuropathy, and muscle weakness. *Vitamin C deficiency* - **Vitamin C** is crucial for **collagen synthesis**, and its deficiency causes **scurvy**, characterized by weakened blood vessels, bleeding gums, and impaired wound healing. - It does not directly affect the mineralization of bone, which is the hallmark of osteomalacia. *None of the options* - This option is incorrect because **Vitamin D deficiency** is a well-established cause of osteomalacia [2].

Q: Which of the following deficiencies is most directly associated with the development of Wernicke's encephalopathy?

Thiamine deficiency. ***Thiamine deficiency*** - **Wernicke's encephalopathy** is a neurological emergency caused by a severe deficiency of **thiamine (vitamin B1)**. - Thiamine is crucial for **glucose metabolism** in the brain, and its deficiency leads to damage in specific brain regions, including the **mammillary bodies** and **thalamus**. *Niacin deficiency* - **Niacin (vitamin B3)** deficiency leads to **pellagra**, characterized by the "3 Ds": **dermatitis**, **diarrhea**, and **dementia**. - While it can cause neurological symptoms, they are distinct from the acute presentation of Wernicke's encephalopathy. *Cobalamin deficiency* - **Cobalamin (vitamin B12)** deficiency can cause **megaloblastic anemia** and neurological symptoms such as **peripheral neuropathy**, **ataxia**, and **cognitive impairment**. - However, it does not directly cause Wernicke's encephalopathy, which has a more acute and characteristic triad of symptoms. *Folate deficiency* - **Folate (vitamin B9)** deficiency primarily causes **megaloblastic anemia** and can be associated with **neural tube defects** in newborns. - While it can contribute to neurological issues, it is not the direct cause of Wernicke's encephalopathy.

Q: Which of the following is most essential for wound healing?

Ascorbic acid. ***Ascorbic acid*** - **Ascorbic acid** (Vitamin C) is crucial for **collagen synthesis** and cross-linking, which are fundamental processes in wound healing. - It acts as a **cofactor** for enzymes like **prolyl hydroxylase**, essential for stabilizing collagen structure, and is a potent **antioxidant** reducing oxidative stress. *Zinc* - While important for cell proliferation and immune function, **zinc** deficiency primarily leads to delayed healing and impaired immune response, not the primary facilitator. - Zinc is a component of many enzymes involved in wound healing, but its role is secondary to the direct collagen synthesis facilitated by Vitamin C. *Vitamin A* - **Vitamin A** supports epithelial cell differentiation and immune response, which are beneficial for wound healing. - However, its primary role is not directly in collagen production or fibroblast function in the same way as ascorbic acid. *Selenium* - **Selenium** is a trace element with antioxidant properties, important for protecting cells from damage. - Its direct involvement in the fundamental processes of collagen synthesis and wound closure is less pronounced compared to ascorbic acid.

Q: Which of the following is absolutely essential for wound healing?

Vitamin C. ***Vit C*** - **Vitamin C** is absolutely essential for wound healing because it is a crucial cofactor for **collagen synthesis**, specifically for the hydroxylation of proline and lysine residues. - Without adequate vitamin C, strong, stable **collagen fibers** cannot be formed, leading to impaired wound tensile strength and delayed healing. *Balanced diet* - While a **balanced diet** provides overall nutritional support for wound healing, it is a general principle, not a single, absolutely essential nutrient in the same way **Vitamin C** is for a specific biochemical process. - A balanced diet incorporates many components, but specifically points to **Vitamin C's** role makes it more specific and thereby the correct answer. *Vit D* - **Vitamin D** plays a role in bone health and immune function but is not directly involved in the **collagen synthesis** or immediate structural integrity of new tissue formation in wound healing to the same critical extent as Vitamin C. - Its effects on wound healing are more indirect, through modulation of inflammation and cell proliferation, rather than being an "absolutely essential" direct component of the healing process. *Carbohydrates* - **Carbohydrates** are important for providing energy for cellular activities during wound healing. - However, they are not directly involved in the **structural integrity** or **collagen formation** of the healing tissue itself, unlike Vitamin C.

Question 1

Active form of Vitamin D is:

Accepted Answer

Calcitriol

Answer

Calcifediol

Answer

Paricalcitol

Answer

Cholecalciferol

Question 2

Glutathione reductase assay is helpful in assessing the deficiency of

Accepted Answer

Riboflavin

Answer

Niacin

Answer

Pyridoxine

Answer

Vit B5

Question 3

All are true regarding vitamin D, except ?

Accepted Answer

1-hydroxylation in liver

Answer

Sunlight is important

Answer

Active form is calcitriol

Answer

RDA for children is 400 IU

Question 4

During the dark phase of visual cycle, which form of vitamin A combines with opsin to make Rhodopsin:

Accepted Answer

11-cis-Retinaldehyde

Answer

11-cis-Retinol

Answer

All trans-Retinol

Answer

All trans-Retinaldehyde

Question 5

All of the following statements are true except:

Accepted Answer

25(OH)D3 is the most active form of vitamin D

Answer

25–α hydroxylation takes place in liver

Answer

1–α hydroxylation takes place in kidney

Answer

Daily requirement in the absence of sun–light is 450-600 IU/day

Question 6

Which of the following cause low serum calcium?

Accepted Answer

Vit D deficiency

Answer

GH

Answer

Hypoparathyroidism

Answer

Glucocorticoids

Question 7

Osteomalacia is due to -

Accepted Answer

Vitamin D deficiency

Answer

Vitamin E deficiency

Answer

Vitamin C deficiency

Answer

None of the options

Question 8

Which of the following deficiencies is most directly associated with the development of Wernicke's encephalopathy?

Accepted Answer

Thiamine deficiency

Answer

Niacin deficiency

Answer

Cobalamin deficiency

Answer

Folate deficiency

Question 9

Which of the following is most essential for wound healing?

Accepted Answer

Ascorbic acid

Answer

Zinc

Answer

Vitamin A

Answer

Selenium

Question 10

Which of the following is absolutely essential for wound healing?

Accepted Answer

Vitamin C

Answer

Balanced diet

Answer

Vitamin D

Answer

Carbohydrates

Vitamins and Coenzymes — MCQs

Vitamins and Coenzymes — MCQs

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