Vitamin E and Antioxidant Functions — MCQs
Most potent lipid phase antioxidant:
At concentrations present in the diet, which vitamin is absorbed primarily by diffusion?
All are sources of free radicals except -
The major carrier of cholesterol in plasma is:
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 person switches from a high-fat diet to a low-fat diet with a compensatory increase in carbohydrates to maintain the same caloric intake. Which lipoprotein is likely to increase?
Which vitamin is considered the most potent antioxidant?
Which mineral is known for its antioxidant properties similar to those of vitamin E?
Vitamin B12 is found maximum in:
Which of the following is the richest source of vitamin B12?
Vitamin E and Antioxidant Functions Indian Medical PG Practice Questions and MCQs
Question 1: 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 2: At concentrations present in the diet, which vitamin is absorbed primarily by diffusion?
- A. Vitamin D (Correct Answer)
- B. Folate
- C. Niacin
- D. Vitamin C
Explanation: ***Vitamin D*** - **Fat-soluble vitamins** (A, D, E, K) like Vitamin D are absorbed from the intestine primarily through **passive diffusion** at **dietary/physiological concentrations**. - They are incorporated into **mixed micelles** in the intestinal lumen, which facilitate their transport to the enterocyte membrane. - The **lipophilic nature** of these vitamins allows them to passively diffuse across the lipid bilayer of the enterocyte membrane **without requiring specific transporters**. - Once inside enterocytes, they are packaged into **chylomicrons** for lymphatic transport. *Vitamin C* - **Water-soluble vitamin C** is absorbed via **sodium-dependent vitamin C transporters (SVCTs)** - specifically SVCT1 in the small intestine. - At high (pharmacological) concentrations, passive diffusion can contribute to its absorption, but at dietary concentrations, active transport predominates. *Folate* - Folate, a **water-soluble B vitamin**, is absorbed primarily through **active transport mechanisms**, specifically via the **reduced folate carrier (RFC)** and **proton-coupled folate transporter (PCFT)**. - These transporters are essential for efficient folate uptake even at low concentrations. *Niacin* - Niacin (**Vitamin B3**) is absorbed through **carrier-mediated transport** at physiological (dietary) concentrations. - At pharmacological doses, simple passive diffusion can dominate, but this is not the primary mechanism at normal dietary levels.
Question 3: All are sources of free radicals except -
- A. Glutathione (Correct Answer)
- B. Nitric oxide
- C. Myeloperoxidase
- D. Fenton's reaction
Explanation: ***Glutathione*** - **Glutathione** is a powerful **antioxidant** that helps to neutralize free radicals, not produce them. - It plays a crucial role in protecting cells from **oxidative damage**. *Nitric oxide* - **Nitric oxide (NO)** is a free radical itself, containing an unpaired electron. - It can lead to the formation of other reactive nitrogen species, contributing to **oxidative stress**. *Myeloperoxidase* - **Myeloperoxidase (MPO)** is an enzyme primarily found in neutrophils that produces powerful free radicals like **hypochlorous acid (HOCl)**, a highly reactive oxidant. - This process is essential for the immune system's ability to kill invading pathogens. *Fenton's reaction* - **Fenton's reaction** is a key chemical process that generates highly reactive **hydroxyl radicals (•OH)** from hydrogen peroxide in the presence of ferrous iron (Fe2+). - This reaction is a significant source of oxidative damage in biological systems.
Question 4: The major carrier of cholesterol in plasma is:
- A. Very-Low-Density Lipoprotein (VLDL)
- B. Low-Density Lipoprotein (LDL) (Correct Answer)
- C. Chylomicrons
- D. High-Density Lipoprotein (HDL)
Explanation: ***Low-Density Lipoprotein (LDL)*** - **LDL** is the **major carrier of cholesterol in plasma**, transporting approximately **60-70% of total plasma cholesterol**. - It is primarily responsible for delivering **cholesterol** from the liver to peripheral tissues for **membrane synthesis**, **steroid hormone production**, and other cellular functions. - LDL cholesterol levels are the primary target for cardiovascular risk assessment and management. *Very-Low-Density Lipoprotein (VLDL)* - **VLDL** primarily transports **triglycerides** (55-65% of its content) synthesized in the liver to peripheral tissues. - While it contains some cholesterol (~10-15%), its main function is **triglyceride delivery**, and it serves as a precursor to LDL in the circulation. *Chylomicrons* - **Chylomicrons** are responsible for transporting **dietary triglycerides** and **cholesterol** from the intestines to tissues. - They are the largest lipoproteins and primarily transport **exogenous (dietary) lipids**. - Cholesterol represents only 3-5% of chylomicron content. *High-Density Lipoprotein (HDL)* - **HDL** carries approximately **20-30% of plasma cholesterol** and plays a crucial role in **reverse cholesterol transport**. - It collects excess cholesterol from peripheral tissues and returns it to the liver for excretion. - While functionally important for cholesterol homeostasis (protective against atherosclerosis), it carries significantly less cholesterol than LDL.
Question 5: 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 6: A person switches from a high-fat diet to a low-fat diet with a compensatory increase in carbohydrates to maintain the same caloric intake. Which lipoprotein is likely to increase?
- A. Chylomicron
- B. IDL
- C. HDL
- D. VLDL (Correct Answer)
Explanation: ***VLDL*** - A low-fat diet with increased **carbohydrates** can lead to increased hepatic synthesis of triglycerides, which are then packaged into **VLDL** particles for transport from the liver. This is because excess carbohydrates can be converted to fatty acids and then to triglycerides in the liver. - The liver's increased triglyceride production, driven by abundant **glucose** from carbohydrates, directly corresponds to a rise in **VLDL** secretion to export these lipids. *Chylomicron* - **Chylomicrons** primarily transport **dietary fats** (exogenous triglycerides) absorbed from the intestine. - Switching to a low-fat diet would typically lead to a *decrease* in chylomicron production, as less dietary fat is available for absorption. *IDL* - **IDL** (Intermediate-Density Lipoprotein) is a remnant of **VLDL** metabolism, formed after VLDL loses some triglycerides. - While VLDL may increase, leading to *more* IDL formation, IDL itself is not the primary component that *increases* directly due to high carbohydrate intake; rather, the precursor **VLDL** is directly affected. *HDL* - **HDL** (High-Density Lipoprotein) is involved in **reverse cholesterol transport**, picking up excess cholesterol from peripheral tissues and returning it to the liver. - High carbohydrate intake, especially refined carbohydrates, can sometimes lead to a *decrease* in HDL levels, not an increase.
Question 7: Which vitamin is considered the most potent antioxidant?
- A. Vit A
- B. Vit K
- C. Vit E (Correct Answer)
- D. Vit C
Explanation: ***Vit E*** - **Vitamin E** is a **lipid-soluble antioxidant** that primarily protects cell membranes from **oxidative damage** by scavenging free radicals. - Its ability to interrupt **lipid peroxidation** makes it highly effective in protecting tissues rich in polyunsaturated fatty acids, such as cell membranes. *Vit A* - **Vitamin A**, particularly in its carotenoid forms like **beta-carotene**, is an antioxidant, but its primary role is in **vision** and **immune function**. - While it can quench **singlet oxygen** and trap free radicals, it is generally considered less potent than vitamin E in protecting against lipid peroxidation. *Vit K* - **Vitamin K** is crucial for **blood coagulation** and **bone metabolism**, but it does not have significant antioxidant properties. - Its primary biological functions are unrelated to scavenging **free radicals** or preventing oxidative stress. *Vit C* - **Vitamin C** is a potent **water-soluble antioxidant** that works in aqueous environments, such as the cytoplasm and extracellular fluid. - While it can neutralize **reactive oxygen species** and regenerate other antioxidants like vitamin E, its solubility limits its direct activity in protecting lipid membranes, making vitamin E more potent in that specific context.
Question 8: Which mineral is known for its antioxidant properties similar to those of vitamin E?
- A. Calcium
- B. Iron
- C. Selenium (Correct Answer)
- D. Magnesium
Explanation: ***Selenium*** - Selenium is a crucial component of **glutathione peroxidase**, an enzyme with significant **antioxidant properties** that protects cells from oxidative damage. - Its antioxidant function is often compared to that of **vitamin E**, as both work to neutralize **free radicals** in the body. *Calcium* - Calcium is primarily known for its role in **bone health**, muscle contraction, and **nerve transmission**, not for its antioxidant properties. - It does not directly participate in neutralizing free radicals like selenium or vitamin E. *Iron* - Iron is essential for **oxygen transport** in red blood cells and various metabolic processes. - While crucial, excessive free iron can actually promote the formation of **free radicals** (Fenton reaction), making it pro-oxidant rather than antioxidant. *Magnesium* - Magnesium is involved in over 300 enzymatic reactions, including **energy metabolism** and muscle and nerve function. - It does not share direct antioxidant properties similar to vitamin E or selenium.
Question 9: Vitamin B12 is found maximum in:
- A. Sunlight
- B. Green leafy vegetables
- C. Animal products (Correct Answer)
- D. Roots and tubers
Explanation: ***Animal products*** - **Vitamin B12**, or cobalamin, is primarily synthesized by bacteria and accumulates in animal tissues, making **meat, fish, poultry, eggs, and dairy** the richest dietary sources. - Humans generally cannot synthesize vitamin B12 and must obtain it from dietary sources, with **animal-derived foods** being the most concentrated and bioavailable forms. *Sunlight* - **Sunlight** is primarily critical for the synthesis of **Vitamin D** in the skin, not Vitamin B12. - Exposure to sunlight has no direct role in the production or absorption of **Vitamin B12**. *Green leafy vegetables* - **Green leafy vegetables** are excellent sources of nutrients like **folate, Vitamin K, and iron**, but they are generally devoid of naturally occurring **Vitamin B12**. - While some fortified plant-based foods may contain Vitamin B12, naturally, these vegetables do not provide it. *Roots and tubers* - **Roots and tubers** like potatoes, carrots, and sweet potatoes are good sources of carbohydrates, fiber, and various vitamins and minerals such as **Vitamin C and potassium**. - They do not contain significant amounts of **Vitamin B12**, as they are plant-based foods.
Question 10: 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.
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