Lipid Metabolism — MCQs

Lipid Metabolism Indian Medical PG Practice Questions and MCQs

Question 701: Which oil has the highest concentration of linolenic acid?

A. Safflower oil
B. Coconut oil
C. Groundnut oil
D. Soyabean oil (Correct Answer)

Explanation: ***Soyabean oil*** - **Soyabean oil** contains approximately **7-10% linolenic acid (C18:3)**, an omega-3 fatty acid. - Among the given options, it has the **highest concentration** of this essential fatty acid. - **Linolenic acid** is crucial for **heart health** and **reducing inflammation**. *Coconut oil* - **Coconut oil** is primarily composed of **saturated fatty acids**, notably **lauric acid (C12:0)**. - It contains **negligible amounts** of **linolenic acid** (<0.5%). *Groundnut oil* - **Groundnut oil** (peanut oil) is rich in **oleic acid (C18:1)** and **linoleic acid (C18:2)**. - Its concentration of **linolenic acid** is very low (**~0.5-1%**), much lower than soyabean oil. *Safflower oil* - **Safflower oil** is known for its high content of **linoleic acid (C18:2)**, an omega-6 fatty acid. - It contains **minimal amounts** of **linolenic acid** (<1%).

Question 702: At which positions does pancreatic lipase hydrolyze the ester linkages of triacylglycerides?

A. 1 and 2
B. 2 and 3
C. Only 3
D. 1 and 3 (Correct Answer)

Explanation: **Correct: 1 and 3** - Pancreatic lipase specifically targets the **ester bonds at the sn-1 and sn-3 positions** (primary alcohol positions) on the glycerol backbone of triacylglycerides. - This positional specificity results in the formation of **2-monoacylglycerol (2-MAG)** and **two free fatty acids**. - This is the characteristic action of pancreatic triacylglycerol lipase during fat digestion in the intestinal lumen. *Incorrect: 1 and 2* - Hydrolysis at positions 1 and 2 would produce a 3-monoacylglycerol and free fatty acids, which is not the physiological product of pancreatic lipase. - The enzyme's positional specificity favors the outer sn-1 and sn-3 positions, not the middle sn-2 position. *Incorrect: 2 and 3* - Hydrolysis at positions 2 and 3 would yield a 1-monoacylglycerol and free fatty acids, which does not reflect pancreatic lipase activity. - The enzyme specifically spares the sn-2 position due to its structural specificity. *Incorrect: Only 3* - If only position 3 were hydrolyzed, the product would be a 1,2-diacylglycerol and one free fatty acid. - This represents incomplete hydrolysis; pancreatic lipase typically hydrolyzes **both outer positions (sn-1 and sn-3)** due to its regiospecificity.

Question 703: Which enzyme is primarily responsible for the fat metabolism in adipose tissue?

A. Lipoprotein lipase
B. Hormone-sensitive lipase (Correct Answer)
C. Acid lipase
D. Acid maltase

Explanation: ***Hormone-sensitive lipase*** - This enzyme is crucial for the **mobilization of stored triglycerides** in adipose tissue by hydrolyzing them into fatty acids and glycerol. - Its activity is stimulated by hormones like **epinephrine** and **norepinephrine** and inhibited by insulin, reflecting its role in regulating fat release during energy demand. *Lipoprotein lipase* - This enzyme is primarily located on the **endothelial surface of capillaries** in various tissues, including adipose tissue, muscle, and heart. - Its main role is to clear **triglyceride-rich lipoproteins** like chylomicrons and VLDL from the bloodstream, facilitating the uptake of fatty acids into cells for storage or energy, rather than direct fat metabolism within the adipose cell. *Acid lipase* - **Lysosomal acid lipase** functions within lysosomes to break down cholesterol esters and triglycerides that are taken up by cells. - Its primary role is in the degradation of lipids within the **lysosomal compartments**, not in the primary process of fat mobilization from adipose tissue stores. *Acid maltase* - Also known as **alpha-glucosidase**, this enzyme is a lysosomal enzyme responsible for breaking down glycogen into glucose. - Its function is related to **glycogen metabolism** and has no direct role in fat metabolism in adipose tissue.

Question 704: The primary site of lipogenesis is:

A. Liver (Correct Answer)
B. Skeletal muscles
C. Myocardium
D. Lungs

Explanation: ***Liver*** - The **liver** is the principal organ for **de novo lipogenesis**, converting excess carbohydrates into fatty acids and triglycerides. - This process is highly active in response to a high-carbohydrate diet, with the synthesized lipids packaged into **VLDL** for transport. *Skeletal muscles* - **Skeletal muscles** primarily utilize fatty acids for **energy production** rather than synthesizing large amounts of new lipids. - While they can store some triglycerides, their capacity for de novo lipogenesis is significantly lower compared to the liver. *Myocardium* - The **myocardium** (heart muscle) primarily relies on fatty acids for its continuous **energy demands** and has limited capacity for de novo lipogenesis. - Its metabolic focus is on efficient **ATP generation** to maintain cardiac function. *Lungs* - The **lungs** are not a primary site for general lipogenesis, though they are involved in the synthesis of specific lipids like **surfactant**. - Surfactant synthesis is a specialized process crucial for lung function, distinct from general energy storage lipogenesis.

Question 705: Which of the following is required for fatty acid synthesis ?

A. NADPH (Correct Answer)
B. NADH
C. FADH₂
D. None of the options

Explanation: ***NADPH*** - **NADPH** is crucial for fatty acid synthesis, providing the **reducing power** needed for the successive reduction steps. - The enzymes involved, such as **fatty acid synthase**, utilize **NADPH** for the conversion of keto groups to hydroxyl groups and then to saturated methylene groups. *NADH* - **NADH** plays a primary role in **oxidative phosphorylation** and the electron transport chain to generate ATP. - It is generally produced during **catabolic reactions** and is not primarily used as a reducing agent in anabolic processes like fatty acid synthesis. *FADH* - **FADH2** (reduced form of FAD, not FADH) is a coenzyme involved in redox reactions, particularly in the **Krebs cycle** and beta-oxidation of fatty acids. - Like NADH, it is mostly involved in **catabolic processes** that generate energy, rather than anabolic processes requiring reducing equivalents for synthesis. *None of the options* - This option is incorrect because **NADPH** is indeed required for fatty acid synthesis, serving as the essential reducing agent. - The other coenzymes mentioned (NADH, FADH) have different metabolic roles, primarily in energy production rather than biosynthesis.

Question 706: Which of the following is a type of 17 OH steroid?

A. Progesterone
B. None of the options
C. Testosterone
D. Cortisol (Correct Answer)

Explanation: ***Cortisol*** - Cortisol is a **glucocorticoid** and is characterized by a **hydroxyl group (-OH)** at the 17th carbon position of its steroid nucleus. - This 17-OH group is crucial for its classification and biological activity as a **17-hydroxycorticosteroid** (17-OH steroid). *Testosterone* - Testosterone is an **androgen** and while it does have a hydroxyl group at the 17β position (making it a 17β-hydroxysteroid), it is NOT classified as a **17-OH steroid (17-hydroxycorticosteroid)**. - The term **"17-OH steroid"** specifically refers to **corticosteroids** with both a hydroxyl at C-17 and a dihydroxyacetone side chain, which testosterone lacks. - Testosterone has a simple hydroxyl at C-17β and lacks the characteristic corticosteroid side chain structure. *Progesterone* - Progesterone is a **progestogen** and lacks a hydroxyl group at the 17th carbon position. - It plays a role in the **menstrual cycle** and **pregnancy** and is primarily characterized by a keto group at C-3 and a two-carbon side chain with a carbonyl group at C-20. *None of the options* - This option is incorrect because **cortisol** is indeed a type of 17-OH steroid (17-hydroxycorticosteroid). - The presence of the 17-hydroxyl group along with the corticosteroid side chain is a defining characteristic of this classification.

Question 707: Which of the following is not affected in Abetalipoproteinemia ?

A. LDL
B. HDL (Correct Answer)
C. IDL
D. VLDL

Explanation: ***HDL*** - **Abetalipoproteinemia** is caused by a defect in the **microsomal triglyceride transfer protein (MTP)**, which is essential for the assembly and secretion of **chylomicrons**, **VLDL**, and subsequently **LDL** and **IDL**. - **HDL synthesis** and secretion occur independently of MTP, as nascent HDL particles are formed in the plasma from lipids and apolipoproteins (primarily apoA-I) released from other lipoproteins and cells. *LDL* - **LDL** is critically affected in abetalipoproteinemia because it is a metabolic product of **VLDL**. - Since **VLDL** production is severely impaired due to the MTP defect, there is a profound deficiency of **LDL** in the plasma. *VLDL* - **VLDL** production is severely impaired in abetalipoproteinemia because **microsomal triglyceride transfer protein (MTP)** is required for its assembly and secretion from the liver. - The inability to load triglycerides onto apoB leads to very low or absent plasma **VLDL** levels. *IDL* - **IDL** is an intermediate lipoprotein in the metabolism of **VLDL** to **LDL**. - Given that both **VLDL** and **LDL** are severely deficient in abetalipoproteinemia, **IDL** levels are also consequently very low or absent.

Question 708: Which of the following statements is true regarding medium chain fatty acids?

A. All of the options are true (Correct Answer)
B. Do not require pancreatic lipase for digestion
C. Absorb directly into portal circulation
D. Are less likely to be deposited in adipose tissue compared to long-chain fatty acids

Explanation: ***All of the options are true*** - This option is correct because medium-chain fatty acids (MCFAs) possess unique metabolic properties that differentiate them from long-chain fatty acids (LCFAs), making all listed statements accurate. - Their shorter chain length allows for distinct digestion, absorption, and metabolic fates, which are beneficial in various clinical contexts. *Do not require pancreatic lipase for digestion* - MCFAs have **shorter carbon chains** (typically 6-12 carbons) and are more hydrophilic than LCFAs. - This property allows them to be digested by **lingual and gastric lipases** to a greater extent, reducing the reliance on pancreatic lipase. *Absorb directly into portal circulation* - Unlike LCFAs, which are re-esterified into triglycerides, packaged into **chylomicrons**, and absorbed into the lymphatic system, MCFAs are absorbed directly into the **portal vein**. - This bypasses the lymphatic system and directly transports them to the liver, making them a rapid energy source. *Are less likely to be deposited in adipose tissue compared to long-chain fatty acids* - MCFAs are **rapidly oxidized** in the liver for energy via beta-oxidation and are less likely to be stored as triglycerides in adipose tissue. - They are also not efficiently utilized for the synthesis of complex lipids or stored fat due to their unique metabolic pathway and preference for oxidation.

Question 709: Which of the following statements about chylomicrons is true?

A. Chylomicrons are unrelated to triglyceride transport.
B. Chylomicrons primarily contain cholesterol.
C. Chylomicrons primarily contain triglycerides (TGs). (Correct Answer)
D. Chylomicrons do not primarily contain triglycerides.

Explanation: ***Chylomicrons primarily contain triglycerides (TGs)*** - **Chylomicrons** are the largest and least dense lipoproteins, primarily responsible for transporting **dietary triglycerides** absorbed from the intestine to peripheral tissues. - They are synthesized in the **enterocytes** of the small intestine and released into the lymphatic system. - Approximately **85-90%** of a chylomicron's mass is composed of **triglycerides**, making them the primary carriers of exogenous fats. *Chylomicrons primarily contain cholesterol* - While chylomicrons do contain some **cholesterol**, it is a minor component (~3-5%) compared to their predominant content, which is **triglycerides**. - Lipoproteins like **LDL** and **HDL** are primarily responsible for cholesterol transport. *Chylomicrons are unrelated to triglyceride transport* - This statement is incorrect; chylomicrons are fundamentally involved in the **transport of dietary triglycerides** from the intestines to various tissues in the body. - After lipoprotein lipase acts on chylomicrons in peripheral tissues, triglycerides are hydrolyzed and fatty acids are taken up by tissues. *Chylomicrons do not primarily contain triglycerides* - This statement directly contradicts the main function and composition of chylomicrons, which are **rich in triglycerides**. - Without triglycerides as their primary content, chylomicrons would not be able to fulfill their physiological role in lipid transport.

Question 710: In which condition does serum appear milky white?

A. Increased LDL
B. Increased HDL
C. Increased VLDL
D. Increased Chylomicrons (Correct Answer)

Explanation: ***Increased Chylomicrons*** - **Chylomicrons** are the largest lipoprotein particles (75-1200 nm) with the highest **triglyceride content (85-95%)**, giving serum a characteristic **milky white** or "creamy" appearance - This intense milky appearance occurs after **fatty meals** (postprandial lipemia) or in **Type I and V hyperlipidemias** (familial chylomicronemia syndrome) - The **light scattering** by these large particles makes the serum completely opaque, distinguishing it from other lipid abnormalities - Classic clinical finding: **"cream layer" forms on top** when lipemic serum stands overnight in refrigerator *Increased LDL* - Elevated **Low-Density Lipoprotein (LDL)** produces **clear to slightly hazy** serum, never milky white - LDL particles are much smaller (18-25 nm) than chylomicrons and contain primarily **cholesterol**, not triglycerides - High LDL is a cardiovascular risk factor but does not cause visible lipemia *Increased HDL* - **High-Density Lipoprotein (HDL)** elevation results in **clear serum** - HDL particles are the smallest (5-12 nm) and densest lipoproteins - High HDL is protective and causes no turbidity *Increased VLDL* - **Very Low-Density Lipoprotein (VLDL)** elevation can cause **turbid or hazy** serum in severe hypertriglyceridemia, but typically less intensely milky than chylomicrons - VLDL particles are smaller (30-80 nm) than chylomicrons with lower triglyceride content (50-65%) - In Type IV hyperlipidemia (isolated VLDL elevation), serum appears uniformly turbid without cream layer formation - The most dramatic "milky white" appearance is specifically associated with **chylomicronemia**

Practice by Chapter

Lipid Classification and Chemistry

Practice Questions

Fatty Acid Oxidation

Practice Questions

Ketone Body Metabolism

Practice Questions

Fatty Acid Synthesis

Practice Questions

Metabolism of Triacylglycerols

Practice Questions

Phospholipid Metabolism

Practice Questions

Cholesterol Metabolism and Biosynthesis

Practice Questions

Bile Acids and Bile Salts

Practice Questions

Lipoprotein Metabolism and Transport

Practice Questions

Dyslipidemias and Atherosclerosis

Practice Questions

Prostaglandins and Eicosanoids

Practice Questions

Fatty Liver and Lipotropic Factors

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free