Lipid Metabolism Practice Questions

Q: Bile acid has a detergent action due to?

Amphipathic nature of bile salts. ***Amphipathic nature of bile salts*** - Bile salts are **amphipathic molecules**, meaning they have both **hydrophilic** (water-loving) and **hydrophobic** (fat-loving) regions. - This dual nature allows them to emulsify fats, breaking large fat globules into smaller ones, thereby exhibiting a **detergent action**. *Formation of soap* - While soaps also have a detergent action due to their amphipathic nature, the primary mechanism of bile acid's detergent action in the body is not through the formation of soap as a product. - Soap formation involves a saponification reaction, which is not the main process explaining bile acid's emulsifying role in digestion. *Formation of zwitter ion* - A **zwitterion** is a molecule possessing both positive and negative charges, resulting in an overall neutral charge. - While bile acids can have ionizable groups, their detergent action is primarily attributed to the separation of hydrophilic and hydrophobic domains, not merely the presence of zwitterionic characteristics. *Formation of medium chain triglycerides* - **Medium-chain triglycerides** are a type of fat molecule; their formation is not responsible for the detergent action of bile acids. - Bile acids aid in the digestion and absorption of various dietary fats, including triglycerides, but they do not form them.

Q: Which of the following is not a glycerophospholipid?

Sphingomyelin. ***Sphingomyelin*** - Sphingomyelin is a **sphingolipid**, characterized by a **sphingosine backbone** rather than a glycerol backbone. - It contains a **phosphate group** and **choline head group** attached to the sphingosine. *Lecithin* - **Lecithin** is another name for **phosphatidylcholine**, which is a **glycerophospholipid**. - It has a **glycerol backbone** esterified to two fatty acids and a phosphate group linked to choline. *Cardiolipin* - **Cardiolipin** is a **glycerophospholipid** composed of two phosphatidic acid moieties linked by another glycerol molecule. - It is unique for having **four fatty acyl chains** and is primarily found in the **inner mitochondrial membrane**. *Plasmalogens* - **Plasmalogens** are a class of **glycerophospholipids** characterized by an **ether linkage** at the sn-1 position of the glycerol backbone, instead of an ester linkage. - They also contain an **ester-linked fatty acid** at the sn-2 position and a phosphate group with a head group.

Q: Which of the following is the rate limiting step in cholesterol synthesis?

HMG CoA reductase. ***HMG CoA reductase*** - **HMG-CoA reductase** catalyzes the conversion of **HMG-CoA** to **mevalonate**, which is the committed and rate-limiting step in cholesterol synthesis. - This enzyme is a major target for **statins**, a class of drugs used to lower cholesterol levels by inhibiting its activity. *Thiokinase* - **Thiokinase** (or fatty acyl-CoA synthetase) is involved in activating fatty acids for metabolism, not directly in cholesterol synthesis. - It catalyzes the formation of **fatty acyl-CoA** from fatty acids and CoA, a step in fatty acid metabolism. *Mevalonate kinase* - **Mevalonate kinase** catalyzes the phosphorylation of mevalonate to **5-phosphomevalonate**. - While essential for cholesterol synthesis, this step occurs after the rate-limiting step and is not the primary regulatory point. *HMG CoA synthase* - **HMG-CoA synthase** catalyzes the condensation of **acetoacetyl-CoA** with **acetyl-CoA** to form **HMG-CoA**. - This step occurs before the reduction of HMG-CoA by HMG-CoA reductase and is not the rate-limiting enzyme in the pathway.

Q: Which mineral is required for cholesterol biosynthesis?

Mg. ***Mg*** - **Magnesium (Mg)** is an essential cofactor for multiple enzymes in **cholesterol biosynthesis**, particularly the **ATP-dependent kinases** in the mevalonate pathway. - **Mevalonate kinase** and **phosphomevalonate kinase** require Mg²⁺ as a cofactor for their catalytic activity. - **Squalene synthase**, which catalyzes the formation of squalene from farnesyl pyrophosphate, also requires Mg²⁺. - Deficiency in magnesium can impair these critical steps in **cholesterol synthesis**. *Fe* - **Iron (Fe)** is vital for many enzymatic reactions, particularly in **oxygen transport** (hemoglobin), **electron transport** (cytochromes), and **energy metabolism**. - It does not function as a cofactor in the enzymatic steps of **cholesterol biosynthesis**. *Mn* - **Manganese (Mn)** serves as a cofactor for enzymes involved in **carbohydrate metabolism**, **bone formation**, and **antioxidant defense** (superoxide dismutase). - While important for various metabolic processes, it is not specifically required for **cholesterol synthesis**. *Cu* - **Copper (Cu)** is a component of several enzymes, including **cytochrome c oxidase** and **superoxide dismutase**, involved in electron transport and antioxidant defense. - It does not play a direct role as a cofactor in the key enzymatic steps of **cholesterol synthesis**.

Q: Which of the following is increased in lipoprotein lipase deficiency?

Chylomicrons. ***Chylomicrons*** - **Lipoprotein lipase (LPL)** is essential for hydrolyzing triglycerides within **chylomicrons** and VLDL, allowing fatty acids to be taken up by tissues. - Deficiency in LPL leads to a significant accumulation of **chylomicrons** in the plasma, as their degradation is impaired, resulting in **hypertriglyceridemia**. *VLDL* - While LPL also breaks down **VLDL**, the primary and most dramatic accumulation in LPL deficiency is seen with **chylomicrons** due to their larger triglyceride content and direct dependence on LPL for clearance after meals. - **VLDL** levels might also be elevated, but the hallmark is the very high **chylomicron** levels. *LDL* - **LDL** is formed from the catabolism of VLDL, and its levels are generally not directly increased due to a primary LPL deficiency. - LPL's main role is in triglyceride-rich lipoprotein metabolism, not directly in **LDL** catabolism. *HDL* - **HDL** plays a role in reverse cholesterol transport and is not directly metabolized by lipoprotein lipase. - In fact, in severe hypertriglyceridemia due to LPL deficiency, **HDL** levels may sometimes be low rather than increased.

Q: Aromatase produces estrogen from -

Androgen. ***Androgen*** - **Aromatase** is an enzyme complex that converts **androgens** (specifically androstenedione and testosterone) into **estrogens** (estrone and estradiol, respectively). - This conversion is a key step in **estrogen biosynthesis** and occurs in various tissues, including the ovaries, placenta, brain, and adipose tissue. *Progesterone* - **Progesterone** is a precursor to androgens, but it is not directly converted to estrogen by aromatase. - It plays a primary role in the **menstrual cycle** and **pregnancy**. *Cortisol* - **Cortisol** is a **glucocorticoid hormone** produced in the adrenal cortex and is not a substrate for aromatase. - Its primary functions relate to stress response, metabolism, and immune regulation. *Aldosterone* - **Aldosterone** is a **mineralocorticoid hormone** produced in the adrenal cortex and is not involved in estrogen synthesis. - It primarily regulates **blood pressure** and electrolyte balance.

Q: A newborn presented with chest retractions, dyspnea, and lethargy. The pediatrician diagnosed the baby with respiratory distress syndrome. This occurs due to the deficiency of:

Lecithin. ***Lecithin*** - **Respiratory distress syndrome (RDS)** in newborns is primarily caused by a deficiency of pulmonary **surfactant**. - **Lecithin (phosphatidylcholine)**, specifically in its dipalmitoyl form (**dipalmitoylphosphatidylcholine or DPPC**), is the main active component of surfactant, constituting ~40-50% of surfactant lipids. - DPPC is crucial for reducing surface tension in the alveoli and preventing their collapse during expiration. - This is the **primary biochemical deficiency** in neonatal RDS. *Dipalmitoyl inositol* - **Inositol** is a sugar alcohol involved in various cellular processes and is present in surfactant as phosphatidylinositol, but it is not a primary functional component. - Deficiency of this compound does not directly lead to **respiratory distress syndrome**. *Dipalmitoylphosphatidylethanolamine* - **Phosphatidylethanolamine (PE)** is a phospholipid found in cell membranes but is not the primary phospholipid responsible for surfactant function. - Note: This is PE, not PC (phosphatidylcholine). While PE is present in surfactant, its deficiency does not specifically cause **neonatal RDS**. *Sphingomyelin* - **Sphingomyelin** is a sphingolipid found in cell membranes and myelin sheaths, but it is not the critical component of pulmonary surfactant. - The **lecithin-to-sphingomyelin (L/S) ratio** is used to assess fetal lung maturity; an L/S ratio >2 indicates mature lungs capable of producing adequate surfactant.

Q: Lipoprotein involved in reverse cholesterol transport?

High-Density Lipoprotein (HDL). ***High-Density Lipoprotein (HDL)*** - **HDL** is often referred to as "good cholesterol" because its primary function is **reverse cholesterol transport**, which removes excess cholesterol from peripheral tissues and returns it to the liver for excretion. - It works by picking up **unesterified cholesterol** from cells and esterifying it via **lecithin-cholesterol acyltransferase (LCAT)**, increasing its lipid content. *Very Low-Density Lipoprotein (VLDL)* - **VLDL** is primarily involved in transporting **endogenous triglycerides** synthesized by the liver to peripheral tissues. - While it carries some cholesterol, its main role is not in reverse cholesterol transport but in delivering lipids. *Intermediate-Density Lipoprotein (IDL)* - **IDL** is a transient lipoprotein formed from **VLDL** after it has shed some triglycerides and apoC-II and apoE. - It can be further metabolized to **LDL** or taken up by the liver; it does not directly participate in reverse cholesterol transport. *Low-Density Lipoprotein (LDL)* - **LDL**, often called "bad cholesterol," is responsible for transporting cholesterol from the liver to peripheral tissues. - High levels of **LDL** are associated with increased risk of **atherosclerosis** due to its role in delivering cholesterol to arterial walls.

Q: In Retinitis pigmentosa, which fatty acid is found to be decreased in the retina?

Docosahexaenoic acid. ***Docosahexaenoic acid*** - **Docosahexaenoic acid (DHA)** is a crucial **omega-3 fatty acid** abundantly found in the **photoreceptor outer segments** of the retina. - Its reduced levels are linked to photoreceptor dysfunction and degeneration seen in conditions like **Retinitis Pigmentosa**, influencing membrane fluidity and visual function. - DHA comprises up to **50% of the fatty acids** in photoreceptor membranes and is essential for maintaining retinal structure and function. *Arachidonic acid* - **Arachidonic acid** is an **omega-6 fatty acid** primarily involved in **inflammatory pathways** and cellular signaling. - While present in the retina, its decrease is not typically associated with the pathogenesis of **Retinitis Pigmentosa**. *Linoleic acid* - **Linoleic acid** is an **omega-6 essential fatty acid** and a precursor to **arachidonic acid**, but it is not a direct structural component of photoreceptor membranes. - Its levels are not specifically decreased in **Retinitis Pigmentosa** as a primary factor. *Palmitic acid* - **Palmitic acid** is a **saturated fatty acid** present in retinal membranes but not specifically concentrated in photoreceptors. - Its levels are not characteristically decreased in **Retinitis Pigmentosa**, unlike the omega-3 fatty acid DHA.

Q: Which of the following helps in the transport of fatty acids across the inner mitochondrial membrane?

Carnitine. ***Carnitine*** - **Carnitine** plays a crucial role in transporting long-chain fatty acids from the **cytosol** into the **mitochondrial matrix** for beta-oxidation. - It acts as a shuttling molecule, forming **acylcarnitine** which can cross the inner mitochondrial membrane via the **carnitine-acylcarnitine translocase**. *Acyl carrier protein* - **Acyl carrier protein (ACP)** is primarily involved in **fatty acid synthesis** in the cytoplasm, not in the transport of fatty acids into mitochondria for degradation. - It carries acyl groups during the elongation reactions of fatty acid synthesis. *Lecithin-cholesterol acyltransferase* - **Lecithin-cholesterol acyltransferase (LCAT)** is an enzyme found in plasma that catalyzes the formation of **cholesterol esters**, which are then transported by lipoproteins. - It is involved in **cholesterol metabolism** and reverse cholesterol transport, not in the mitochondrial transport of fatty acids. *Carnitine and albumin* - While **carnitine** is essential for mitochondrial fatty acid transport, **albumin** transports fatty acids in the blood plasma, from adipose tissue to other tissues. - Albumin does not transport fatty acids across the inner mitochondrial membrane; its role is extra-mitochondrial and related to systemic transport.

Question 1

Bile acid has a detergent action due to?

Accepted Answer

Amphipathic nature of bile salts

Answer

Formation of medium chain triglycerides

Answer

Formation of soap

Answer

Formation of zwitter ion

Question 2

Which of the following is not a glycerophospholipid?

Accepted Answer

Sphingomyelin

Answer

Lecithin

Answer

Cardiolipin

Answer

Plasmalogens

Question 3

Which of the following is the rate limiting step in cholesterol synthesis?

Accepted Answer

HMG CoA reductase

Answer

Thiokinase

Answer

Mevalonate kinase

Answer

HMG CoA synthase

Question 4

Which mineral is required for cholesterol biosynthesis?

Accepted Answer

Mg

Answer

Fe

Answer

Mn

Answer

Cu

Question 5

Which of the following is increased in lipoprotein lipase deficiency?

Accepted Answer

Chylomicrons

Answer

VLDL

Answer

LDL

Answer

HDL

Question 6

Aromatase produces estrogen from -

Accepted Answer

Androgen

Answer

Progesterone

Answer

Cortisol

Answer

Aldosterone

Question 7

A newborn presented with chest retractions, dyspnea, and lethargy. The pediatrician diagnosed the baby with respiratory distress syndrome. This occurs due to the deficiency of:

Accepted Answer

Lecithin

Answer

Dipalmitoyl inositol

Answer

Dipalmitoylphosphatidylethanolamine

Answer

Sphingomyelin

Question 8

Lipoprotein involved in reverse cholesterol transport?

Accepted Answer

High-Density Lipoprotein (HDL)

Answer

Very Low-Density Lipoprotein (VLDL)

Answer

Intermediate-Density Lipoprotein (IDL)

Answer

Low-Density Lipoprotein (LDL)

Question 9

In Retinitis pigmentosa, which fatty acid is found to be decreased in the retina?

Accepted Answer

Docosahexaenoic acid

Answer

Arachidonic

Answer

Palmitic acid

Answer

Linoleic acid

Question 10

Which of the following helps in the transport of fatty acids across the inner mitochondrial membrane?

Accepted Answer

Carnitine

Answer

Acyl carrier protein

Answer

Lecithin-cholesterol acyltransferase

Answer

Carnitine and albumin

Lipid Metabolism — MCQs

Lipid Metabolism — MCQs

On this page

Practice by Chapter

Want unlimited practice?