Lipid Metabolism Practice Questions

Q: In Familial hypercholesterolemia, there is a deficiency of which of the following?

LDL receptor. **Explanation:** **Familial Hypercholesterolemia (FH)** is an autosomal dominant disorder characterized by a defect in the **LDL receptor (LDLR)**. Under normal physiological conditions, the LDL receptor on the liver and peripheral tissues recognizes **Apo B-100** to internalize LDL particles via receptor-mediated endocytosis. A deficiency or mutation in these receptors leads to decreased clearance of LDL from the plasma, resulting in severe hypercholesterolemia and premature atherosclerosis. **Analysis of Options:** * **Option A (Correct):** LDL receptor deficiency is the primary cause of Type IIa Hyperlipoproteinemia (FH). * **Option B (Incorrect):** **Apoprotein A-I** is the major structural protein of HDL and activates LCAT. Its deficiency is associated with Tangier disease, not FH. * **Option C (Incorrect):** **Apoprotein C-II** is a cofactor for Lipoprotein Lipase (LPL). Deficiency leads to Type I Hyperlipoproteinemia (Hyperchylomicronemia). * **Option D (Incorrect):** **Lipoprotein Lipase (LPL)** deficiency prevents the hydrolysis of triglycerides in chylomicrons and VLDL, leading to Type I Hyperlipoproteinemia, characterized by eruptive xanthomas and pancreatitis. **High-Yield Clinical Pearls for NEET-PG:** * **Genetics:** FH is most commonly due to mutations in the *LDLR* gene, but can also be caused by mutations in **Apo B-100** (ligand defect) or **PCSK9** (increased receptor degradation). * **Clinical Features:** Look for **Tendon Xanthomas** (pathognomonic, especially Achilles tendon), Xanthelasma, and Corneal Arcus at a young age. * **Classification:** It is classified as **Type IIa** (elevated LDL only) or **Type IIb** (elevated LDL and VLDL) in the Fredrickson classification. * **Treatment:** Statins are the first-line therapy as they upregulate the expression of remaining functional LDL receptors.

Q: A 6-month-old infant is brought to the emergency department with lethargy, vomiting, and poor feeding. The episode occurred after prolonged fasting. Laboratory results reveal hypoglycemia, low ketone levels (hypoketosis), and mild hepatomegaly. These findings suggest a defect in fat metabolism. Which of the following is the most likely underlying disorder?

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency. ***Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency*** - This disorder is the most common defect of **fatty acid oxidation** and is characterized by the inability to break down medium-chain fatty acids during fasting, leading to severe **hypoglycemia**. - The hallmark finding is **hypoketosis** (low ketones), as the inability to generate acetyl-CoA from fatty acid breakdown means the substrate required for **ketogenesis** is unavailable. *Hers disease* - This is **Glycogen Storage Disease type VI**, involving a deficiency in **liver glycogen phosphorylase**, leading to impaired glycogenolysis and fasting hypoglycemia. - However, GSD type VI does not impair **beta-oxidation**; hence, patients usually maintain the ability to produce adequate **ketone bodies** during periods of fasting. *Hereditary fructose intolerance* - This disorder is a defect of **aldolase B** and causes symptoms (vomiting, lethargy, hypoglycemia) only after the introduction of **dietary fructose** or sucrose. - The acute symptoms are due to **phosphate trapping** and subsequent inhibition of gluconeogenesis, which is dependent on dietary exposure rather than prolonged fasting alone. *Glycogen storage disease type I (Von Gierke disease)* - This condition, caused by a deficiency of **glucose-6-phosphatase**, leads to profound fasting hypoglycemia, significant hepatomegaly, and **lactic acidosis**. - Unlike MCAD deficiency, Von Gierke disease primarily causes defects in glucose release but generally maintains or even increases **ketone body production** (hyperketosis) because fat breakdown is often accelerated.

Q: Which source and cell produce testosterone?

Cholesterol and Leydig cells. ***Cholesterol and Leydig cells***- **Testosterone** is a steroid hormone, and like all steroid hormones (glucocorticoids, mineralocorticoids, estrogen), it is derived from the precursor molecule, **cholesterol**.- The primary source of testosterone production in the male testes is the **Leydig cells** (interstitial cells), stimulated by **Luteinizing Hormone (LH)**.*Cholesterol and Sertoli cells*- While **cholesterol** is the accurate precursor (source), **Sertoli cells** are mainly responsible for supporting **spermatogenesis** and producing **androgen-binding protein (ABP)** and **inhibin**.- Sertoli cells regulate the testicular microenvironment and are primarily stimulated by **FSH**, not for testosterone synthesis.*Dihydrotestosterone and Leydig cells*- **Dihydrotestosterone (DHT)** is a potent *metabolite* formed from testosterone via the enzyme **5-alpha reductase**, not the precursor for testosterone synthesis itself.- Although **Leydig cells** are the site of testosterone production, the initial source must be **cholesterol**, making DHT incorrect.*FSH and Leydig cells*- **FSH** (Follicle-Stimulating Hormone) primarily targets the **Sertoli cells** to promote sperm development and inhibin production.- The pituitary hormone that stimulates **Leydig cells** to synthesize testosterone from cholesterol is **Luteinizing Hormone (LH)**.

Q: A 90 kg obese man is taking a carbohydrate-rich diet. Which of the following enzymes/intermediates will be elevated in him? 1. Malonyl CoA 2. Acetyl CoA Carboxylase 3. PDH 4. Citrate Lyase

$1,2,3,4$. ***Correct Answer: 1,2,3,4 (All of them)*** In an obese person consuming a carbohydrate-rich diet, **high insulin levels** drive maximum flux through **lipogenesis (fatty acid synthesis)**. This results in elevation of ALL enzymes and intermediates in the pathway: - **PDH (Pyruvate Dehydrogenase)**: Activated by insulin to convert pyruvate → Acetyl CoA in mitochondria - **Citrate Lyase**: Elevated to cleave citrate → cytosolic Acetyl CoA (substrate for fatty acid synthesis) - **Acetyl CoA Carboxylase (ACC)**: The **rate-limiting enzyme** of fatty acid synthesis, activated by insulin (dephosphorylation) and citrate - **Malonyl CoA**: The **first committed intermediate** in fatty acid synthesis, product of ACC action on Acetyl CoA All four components work sequentially in the pathway from glucose → fatty acids, and all are upregulated in this metabolic state. *Incorrect Option: 1,2,3* This incorrectly excludes **Citrate Lyase**, which is essential for providing cytosolic Acetyl CoA from mitochondrial citrate. Without elevated Citrate Lyase activity, fatty acid synthesis cannot proceed efficiently despite high carbohydrate intake. *Incorrect Option: 2,3,4* This incorrectly excludes **Malonyl CoA**, the direct product of Acetyl CoA Carboxylase and the committed intermediate for fatty acid synthesis. When ACC is highly active (as it would be with high insulin), Malonyl CoA concentration must be elevated. *Incorrect Option: 1,3,4* This incorrectly excludes **Acetyl CoA Carboxylase (ACC)**, the **rate-limiting enzyme** of the entire fatty acid synthesis pathway. In a high carbohydrate/high insulin state, ACC is maximally activated by dephosphorylation and allosteric activation by citrate, making this a critical error.

Q: Consider the following statements with reference to 'trans fatty acids' : 1. They are geometrical isomers of cis-unsaturated fatty acids. 2. Though atherogenic, being unsaturated they are less so than saturated fatty acids. 3. It takes years for trans fatty acids to be flushed from the body. 4. They lower both LDL cholesterol and HDL cholesterol in the body. Which of the statements given above are correct ?

1 only. ***1 only*** - **Statement 1 is CORRECT**: Trans fatty acids are **geometrical isomers of cis-unsaturated fatty acids**, differing in the spatial arrangement of hydrogen atoms around the carbon-carbon double bond. This structural difference gives them physical and biological properties more similar to saturated fats. - **Statement 2 is INCORRECT**: Trans fatty acids are **MORE atherogenic** than saturated fatty acids, not less. They raise LDL cholesterol and lower HDL cholesterol more significantly than saturated fats. - **Statement 3 is INCORRECT**: Trans fatty acids are metabolized and eliminated from the body within **days to weeks**, not years. Long-term cardiovascular damage results from chronic dietary exposure, not slow elimination kinetics. - **Statement 4 is INCORRECT**: Trans fatty acids **raise LDL cholesterol** ("bad" cholesterol) and **lower HDL cholesterol** ("good" cholesterol). They do not lower both as stated. *1 and 3 only* - Statement 1 is correct, but statement 3 is **incorrect**. The body processes and eliminates trans fatty acids relatively quickly (days to weeks), not years. The detrimental cardiovascular effects accumulate due to chronic dietary exposure, not slow metabolism of individual molecules. *2, 3 and 4* - All three statements are **incorrect**. Statement 2 is wrong because trans fats are **more atherogenic** than saturated fats. Statement 3 is wrong because trans fats are metabolized within weeks, not years. Statement 4 is wrong because trans fats **raise LDL** (not lower it) while lowering HDL. *1, 3 and 4* - Only statement 1 is correct. Statement 3 is **incorrect** as trans fatty acids are metabolized within weeks, not years. Statement 4 is **incorrect** because trans fatty acids **increase LDL cholesterol** and **decrease HDL cholesterol** - they do not lower both.

Q: Which of the following are unsaturated fatty acids? 1. Lauric acid 2. Linoleic acid 3. Oleic acid 4. Palmitic acid Select the correct answer using the code given below.

2 and 3. ***2 and 3*** - **Linoleic acid** is an **omega-6 fatty acid** with two double bonds, making it polyunsaturated. - **Oleic acid** is an **omega-9 fatty acid** with one double bond, making it monounsaturated. *1 and 4* - **Lauric acid** is a **saturated fatty acid** with no double bonds. - **Palmitic acid** is also a **saturated fatty acid** with no double bonds. *1 and 2* - While **linoleic acid** (2) is unsaturated, **lauric acid** (1) is a saturated fatty acid. - This option incorrectly includes a saturated fatty acid. *3 and 4* - While **oleic acid** (3) is unsaturated, **palmitic acid** (4) is a saturated fatty acid. - This option incorrectly includes a saturated fatty acid.

Q: Which of the following fats has the highest concentration of saturated fatty acids ?

Coconut oil. ***Coconut oil*** - **Coconut oil** has the **highest concentration of saturated fatty acids** among common dietary fats, with approximately **82-92% of its total fatty acids being saturated**. - The predominant saturated fatty acid is **lauric acid (C12:0)**, which comprises roughly **45-50%** of its fatty acid profile. - This exceptionally high saturation contributes to its **solid consistency** at room temperature and its stability during cooking. *Butter* - **Butter** is a dairy product containing approximately **50-65% saturated fatty acids**, which is significantly less than coconut oil. - It contains a mix of short-chain, medium-chain, and long-chain saturated fats, along with **monounsaturated** and **polyunsaturated** fats, and **cholesterol**. *Margarine* - **Margarine** was traditionally made from **partially hydrogenated vegetable oils**, leading to high **trans fat** content and variable saturated fat levels. - Modern formulations use **non-hydrogenated or interesterified oils** to reduce trans fats, with saturated fat content varying widely (10-80%) depending on the source oils and processing methods. *Palm oil* - **Palm oil** contains approximately **49-52% saturated fatty acids**, primarily **palmitic acid (C16:0)**, which makes up about 44% of its total fat content. - While high in saturated fat compared to most vegetable oils, it contains substantially less saturated fat than **coconut oil**.

Q: Which of the following dietary sources contains the lowest percent of linoleic acid?

Coconut oil. ***Coconut oil*** - Coconut oil is primarily composed of **saturated fats**, particularly **lauric acid**, and has a very low percentage of linoleic acid. - Its high saturated fat content distinguishes it from most other vegetable oils, which are generally rich in unsaturated fats. *Corn oil* - Corn oil is a **polyunsaturated fatty acid (PUFA)**-rich oil, with a significant proportion of **linoleic acid** (an omega-6 fatty acid). - It is often used in cooking for its neutral flavor and high smoke point. *Mustard oil* - Mustard oil contains a substantial amount of **monounsaturated fatty acids (MUFA)**, like **erucic acid**, and also a notable percentage of **linoleic acid**. - Its distinct pungent flavor is popular in certain cuisines. *Groundnut oil* - Groundnut oil, also known as peanut oil, is rich in both **monounsaturated** and **polyunsaturated fatty acids**, including a good percentage of **linoleic acid**. - It is commonly used for frying due to its high smoke point and mild flavor.

Q: Which one of the following is a polyunsaturated fatty acid ?

Linoleic acid. ***Linoleic acid*** - **Linoleic acid** contains **two double bonds** in its carbon chain making it a **polyunsaturated fatty acid (PUFA)**. - It is an **omega-6 fatty acid**, and an essential fatty acid, meaning it cannot be synthesized by the human body and must be obtained from the diet. *Stearic acid* - **Stearic acid** is a **saturated fatty acid** with no double bonds in its hydrocarbon chain. - Saturated fatty acids are typically solid at room temperature and primarily found in animal fats. *Oleic acid* - **Oleic acid** is a **monounsaturated fatty acid (MUFA)**, meaning it contains only **one double bond** in its carbon chain. - It is an **omega-9 fatty acid**, commonly found in olive oil. *Palmitic acid* - **Palmitic acid** is also a **saturated fatty acid**, similar to stearic acid, with no double bonds. - It is one of the most common saturated fatty acids in animals and plants and is a major component of palm oil.

Q: Consider the following: 1. Coconut oil 2. Groundnut oil 3. Mustard oil Which of the above is/are dietary sources of linoleic acid?

2 and 3 only. ***2 and 3 only*** - **Groundnut oil** (peanut oil) is a good source of **linoleic acid** (omega-6 fatty acid), containing around 20-40% of this polyunsaturated fat. - **Mustard oil** also contains a significant amount of **linoleic acid**, typically ranging from 9% to 21% of its total fatty acid content. *1, 2 and 3* - **Coconut oil** is primarily composed of **saturated fats**, particularly **lauric acid**, and contains very little linoleic acid. - While groundnut and mustard oil are sources, coconut oil is not. *1 and 2 only* - This option incorrectly includes **coconut oil** as a source of linoleic acid, which it is not. - It also excludes **mustard oil**, which is a dietary source of linoleic acid. *3 only* - This option is incomplete as it correctly identifies **mustard oil** but fails to include **groundnut oil**, which is also a significant source of linoleic acid. - Many common vegetable oils are rich in linoleic acid, not just mustard oil.

Question 1

In Familial hypercholesterolemia, there is a deficiency of which of the following?

Accepted Answer

LDL receptor

Answer

Apoprotein A

Answer

Apoprotein C

Answer

Lipoprotein lipase

Question 2

A 6-month-old infant is brought to the emergency department with lethargy, vomiting, and poor feeding. The episode occurred after prolonged fasting. Laboratory results reveal hypoglycemia, low ketone levels (hypoketosis), and mild hepatomegaly. These findings suggest a defect in fat metabolism. Which of the following is the most likely underlying disorder?

Accepted Answer

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency

Answer

Glycogen storage disease type I (Von Gierke disease)

Answer

Hers disease

Answer

Hereditary fructose intolerance

Question 3

Which source and cell produce testosterone?

Accepted Answer

Cholesterol and Leydig cells

Answer

Dihydrotestosterone and Leydig cells

Answer

FSH and Leydig cells

Answer

Cholesterol and Sertoli cells

Question 4

A 90 kg obese man is taking a carbohydrate-rich diet. Which of the following enzymes/intermediates will be elevated in him? 1. Malonyl CoA 2. Acetyl CoA Carboxylase 3. PDH 4. Citrate Lyase

Accepted Answer

$1,2,3,4$

Answer

$1,2,3$

Answer

$1,3,4$

Answer

$2,3,4$

Question 5

Consider the following statements with reference to 'trans fatty acids' :

1. They are geometrical isomers of cis-unsaturated fatty acids.

2. Though atherogenic, being unsaturated they are less so than saturated fatty acids.

3. It takes years for trans fatty acids to be flushed from the body.

4. They lower both LDL cholesterol and HDL cholesterol in the body. Which of the statements given above are correct ?

Accepted Answer

1 only

Answer

1 and 3 only

Answer

2, 3 and 4

Answer

1, 3 and 4

Question 6

Which of the following are unsaturated fatty acids?

1. Lauric acid
2. Linoleic acid
3. Oleic acid
4. Palmitic acid
Select the correct answer using the code given below.

Accepted Answer

2 and 3

Answer

1 and 4

Answer

1 and 2

Answer

3 and 4

Question 7

Which of the following fats has the highest concentration of saturated fatty acids ?

Accepted Answer

Coconut oil

Answer

Butter

Answer

Margarine

Answer

Palm oil

Question 8

Which of the following dietary sources contains the lowest percent of linoleic acid?

Accepted Answer

Coconut oil

Answer

Corn oil

Answer

Mustard oil

Answer

Groundnut oil

Question 9

Which one of the following is a polyunsaturated fatty acid ?

Accepted Answer

Linoleic acid

Answer

Stearic acid

Answer

Oleic acid

Answer

Palmitic acid

Question 10

Consider the following:

1. Coconut oil
2. Groundnut oil
3. Mustard oil

Which of the above is/are dietary sources of linoleic acid?

Accepted Answer

2 and 3 only

Answer

1, 2 and 3

Answer

1 and 2 only

Answer

3 only

Lipid Metabolism — MCQs

Lipid Metabolism — MCQs

On this page

Practice by Chapter

Want unlimited practice?