Lipid Metabolism — MCQs

Lipid Metabolism Indian Medical PG Practice Questions and MCQs

Question 681: HDL is called good cholesterol because -

A. Removes cholesterol from peripheral tissues (Correct Answer)
B. Increases cholesterol delivery to peripheral tissues
C. Stimulates cholesterol synthesis in the liver
D. Activates enzymes that break down triglycerides

Explanation: ***Removes cholesterol from peripheral tissues*** - **High-density lipoprotein (HDL)** is known as "good cholesterol" due to its role in **reverse cholesterol transport**, a process where it collects excess cholesterol from peripheral cells and tissues. - This action helps to prevent the accumulation of cholesterol in arteries, thereby reducing the risk of **atherosclerosis** and cardiovascular disease. - HDL then transports this cholesterol to the liver for excretion via bile, completing the protective cycle. *Increases cholesterol delivery to peripheral tissues* - This is actually the opposite of HDL's function and describes the role of **LDL (low-density lipoprotein)**, which is considered "bad cholesterol." - LDL delivers cholesterol to peripheral tissues, and excess LDL can lead to **atherosclerotic plaque formation**. *Stimulates cholesterol synthesis in the liver* - HDL does not directly stimulate cholesterol synthesis in the liver; rather, its role is primarily in **cholesterol efflux** from cells and transport. - The liver's cholesterol synthesis is regulated by various factors, including dietary intake and cellular cholesterol levels via the **SREBP pathway**, but HDL does not upregulate hepatic cholesterol synthesis. *Activates enzymes that break down triglycerides* - While HDL does activate **LCAT (lecithin-cholesterol acyltransferase)** for cholesterol esterification, its primary "good" function is not the breakdown of triglycerides. - **Lipoprotein lipase (LPL)** is the primary enzyme responsible for triglyceride breakdown in lipoproteins like VLDL and chylomicrons.

Question 682: Cholesterol is not a precursor for the synthesis of which of the following?

A. Testosterone
B. Lipocortin (Correct Answer)
C. Cortisol
D. Aldosterone

Explanation: ***Lipocortin*** - **Lipocortin** (also known as annexin A1) is a **protein**, not a steroid compound - It is synthesized via **protein translation** from mRNA, not from cholesterol - Mediates anti-inflammatory effects of glucocorticoids and is involved in cell growth regulation - **Key point:** Only steroids and bile acids are derived from cholesterol, not proteins *Testosterone* - **Testosterone** is an androgen (male sex hormone) **synthesized from cholesterol** - Cholesterol → Pregnenolone → DHEA → Androstenedione → Testosterone - Produced in the gonads (Leydig cells) and adrenal glands *Cortisol* - **Cortisol** is a glucocorticoid hormone **derived from cholesterol** - Cholesterol → Pregnenolone → 17-hydroxypregnenolone → Cortisol - Synthesized in the zona fasciculata of the adrenal cortex *Aldosterone* - **Aldosterone** is a mineralocorticoid hormone **synthesized from cholesterol** - Cholesterol → Pregnenolone → Progesterone → Aldosterone - Produced in the zona glomerulosa of the adrenal cortex

Question 683: Apo B48 is synthesized in -

A. Liver
B. Kidney
C. Intestine (Correct Answer)
D. RBCs

Explanation: ***Intestine*** - **Apo B48** is a truncated form of apolipoprotein B-100, uniquely synthesized in the **intestine** through RNA editing. - It is a crucial structural component of **chylomicrons**, which are lipoprotein particles responsible for transporting exogenous dietary lipids from the intestine to other tissues. *Liver* - The liver primarily synthesizes **Apo B100**, which is a full-length apolipoprotein B and a major component of VLDL, IDL, and LDL. - It does not produce Apo B48. *Kidney* - The kidneys are involved in filtering waste products and regulating fluid balance, but they do not play a role in the synthesis of apolipoproteins like Apo B48. - Kidney cells are not equipped with the specific machinery for Apo B mRNA editing. *RBCs* - Red blood cells (RBCs) are primarily responsible for oxygen transport and lack a nucleus and most organelles, including those required for protein synthesis. - Therefore, RBCs cannot synthesize proteins such as Apo B48.

Question 684: Which of the following stimulates Acetyl CoA Carboxylase?

A. Starvation
B. Glucagon
C. Citrate (Correct Answer)
D. None of the options

Explanation: ***Citrate*** - **Citrate** is an allosteric activator of **Acetyl-CoA Carboxylase (ACC)**, indicating abundant energy and precursor availability for fatty acid synthesis. - This activation promotes the conversion of **Acetyl-CoA** to **Malonyl-CoA**, the committed step in **fatty acid synthesis**. *Starvation* - **Starvation** leads to energy deficit, which generally **inhibits** anabolic processes like fatty acid synthesis. - In this state, enzymes involved in anabolic pathways are often downregulated or inhibited to conserve energy. *Glucagon* - **Glucagon** is a hormone that signals low blood glucose and promotes catabolic processes such as **glycogenolysis** and **gluconeogenesis**. - It **inhibits** fatty acid synthesis by phosphorylating and inactivating **Acetyl-CoA Carboxylase**, thus opposing citrate's activating effect. *None of the options* - **Citrate** is a known stimulator of Acetyl CoA Carboxylase. - This option is incorrect because there is a correct answer among the choices.

Question 685: Which of the following statements about adiponectin is incorrect?

A. Secreted by adipose tissue
B. Increases FFA oxidation
C. Lowers glucose
D. Positive Correlation with BMI (Correct Answer)

Explanation: ***Positive Correlation with BMI (INCORRECT STATEMENT)*** - Adiponectin levels are **inversely correlated with BMI**, NOT positively correlated; as BMI increases, adiponectin levels generally decrease. - This inverse relationship is significant because lower adiponectin levels are associated with increased insulin resistance and **metabolic syndrome**. - This statement is **false**, making it the correct answer to this question. *Secreted by adipose tissue (Correct statement)* - Adiponectin is a **hormone primarily secreted by adipocytes** (fat cells). - It plays a crucial role in regulating glucose and lipid metabolism, and its secretion is altered in conditions like obesity. - This statement is **true**. *Lowers glucose (Correct statement)* - Adiponectin **enhances insulin sensitivity** in peripheral tissues like skeletal muscle and liver, leading to increased glucose uptake and utilization. - This action helps to **lower blood glucose levels** and improve glycemic control. - This statement is **true**. *Increases FFA oxidation (Correct statement)* - Adiponectin **promotes fatty acid oxidation** in muscle and liver, reducing intracellular lipid accumulation. - By increasing fatty acid burning, it helps to **decrease circulating free fatty acid (FFA) levels**, which can contribute to insulin resistance if elevated. - This statement is **true**.

Question 686: What is the effect of moderate alcohol consumption on lipid profiles in dyslipidemia?

A. Decreased HDL levels
B. Increased HDL levels (Correct Answer)
C. Increased triglyceride levels
D. Decreased LDL levels

Explanation: ***Increased HDL levels*** - Moderate alcohol consumption is known to **increase high-density lipoprotein (HDL) cholesterol levels**, which is often considered beneficial for cardiovascular health. - This effect is thought to be mediated by alcohol's influence on **hepatic lipoprotein metabolism**, leading to enhanced HDL production and reduced catabolism. *Decreased HDL levels* - This is incorrect, as multiple studies have consistently shown that **moderate alcohol consumption** tends to elevate, rather than decrease, HDL cholesterol. - Low HDL levels are associated with increased cardiovascular risk, making this effect an undesirable outcome that is not typical of moderate drinking. *Increased triglyceride levels* - While heavy or chronic alcohol consumption can lead to **increased triglyceride levels**, moderate intake typically has a neutral or only slightly elevated effect, if any, often overshadowed by the HDL increase. - Significant hypertriglyceridemia is a concern with **excessive alcohol use**, not usually with moderate consumption in healthy individuals. *Decreased LDL levels* - Moderate alcohol consumption generally has **little to no significant effect** on **low-density lipoprotein (LDL) cholesterol levels**, often referred to as "bad" cholesterol. - While HDL increases are observed, alcohol does not effectively lower LDL, which is a primary target in the management of dyslipidemia.

Question 687: What is the primary effect of moderate alcohol consumption on cholesterol levels?

A. Total cholesterol
B. Low-Density Lipoprotein (LDL)
C. Very Low-Density Lipoprotein (VLDL)
D. High-Density Lipoprotein (HDL) (Correct Answer)

Explanation: ***High-Density Lipoprotein (HDL)*** - Moderate alcohol consumption is known to **increase HDL cholesterol** levels. - HDL cholesterol helps in the **reverse cholesterol transport**, removing excess cholesterol from tissues and transporting it back to the liver for excretion. *Total cholesterol* - The effect of moderate alcohol on **total cholesterol** is less consistent and may vary, as it is a sum of HDL, LDL, and 20% of VLDL. - While HDL increases, other components might remain unchanged or show minimal variation, thus not making it the primary and direct effect. *Low-Density Lipoprotein (LDL)* - Moderate alcohol consumption generally has **little to no significant effect** on **LDL cholesterol** levels. - Some studies suggest a slight decrease or no change, but it is not the primary lipid affected. *Very Low-Density Lipoprotein (VLDL)* - There is generally **no significant direct effect** of moderate alcohol consumption on **VLDL cholesterol** levels. - Excessive alcohol intake, however, can elevate triglycerides, which are the main component of VLDL particles.

Question 688: Which of the following is not a phospholipid ?

A. Lecithin
B. Plasmalogen
C. Cardiolipin
D. Ganglioside (Correct Answer)

Explanation: ***Ganglioside*** - Gangliosides are a type of **glycosphingolipid** because their structure includes a ceramide (a sphingoid base linked to a fatty acid) and a carbohydrate portion with one or more **sialic acid** residues, but no phosphate group. - They are primarily found in **nerve cell membranes** and are crucial for cell-cell recognition and signaling, differentiating them from phospholipids which contain a phosphate group. *Lecithin* - Lecithin, specifically **phosphatidylcholine**, is a common phospholipid characterized by a **phosphate group** and a **choline head group** attached to a diacylglycerol backbone. - It plays vital roles in cell membrane structure and function and is an important emulsifier. *Plasmalogen* - Plasmalogens are a class of phospholipids characterized by a **vinyl ether linkage** at the *sn*-1 position of the glycerol backbone, instead of the typical ester linkage found in other phospholipids. - They retain the defining **phosphate group** that classifies them as phospholipids. *Cardiolipin* - Cardiolipin is a unique phospholipid composed of **two phosphatidic acid moieties** connected by a glycerol molecule, resulting in four fatty acid chains and two phosphate groups. - It is predominantly found in the **inner mitochondrial membrane**, essential for mitochondrial function.

Question 689: Which of the following is not an androgen?

A. 17α-hydroxyprogesterone (Correct Answer)
B. Testosterone
C. Dihydrotestosterone
D. Androstenedione

Explanation: ***17α-hydroxyprogesterone*** - This is a **progesterone derivative** and an intermediate in the synthesis of androgens and corticosteroids, but it does **not possess significant androgenic activity** itself. - Its primary role is as a precursor, rather than a direct androgen. *Testosterone* - **Testosterone** is the **primary male sex hormone** and a potent androgen, responsible for the development of male secondary sexual characteristics. - It plays crucial roles in muscle mass, bone density, libido, and erythropoiesis. *Dihydrotestosterone* - **Dihydrotestosterone (DHT)** is a potent androgen, formed from testosterone by the enzyme 5α-reductase. - DHT is responsible for the development of external male genitalia during fetal development and contributes to prostate growth and male pattern baldness in adults. *Androstenedione* - **Androstenedione** is a **weak androgen** and an important **precursor hormone** in the biosynthesis of testosterone and estrogens. - It is produced in the adrenal glands and gonads, serving as an intermediate step in steroidogenesis.

Question 690: Concentration of which is inversely related to the risk of coronary heart disease?

A. VLDL
B. LDL
C. HDL (Correct Answer)
D. None of the options

Explanation: ***HDL*** - **High-density lipoprotein (HDL)** is known as "good cholesterol" because it helps remove excess cholesterol from the arteries and transport it back to the liver for excretion. - Higher levels of HDL are generally associated with a **lower risk of coronary heart disease (CHD)**, hence the inverse relationship. *VLDL* - **Very low-density lipoprotein (VLDL)** carries triglycerides and cholesterol and is considered an independent risk factor for CHD when present in high concentrations. - High VLDL levels are associated with an **increased risk of CHD**, not an inverse relationship. *LDL* - **Low-density lipoprotein (LDL)** is often referred to as "bad cholesterol" because it contributes to plaque buildup in arteries (**atherosclerosis**). - High levels of LDL are strongly associated with an **increased risk of CHD**, indicating a direct, not inverse, relationship. *None of the options* - This option is incorrect because HDL clearly demonstrates an **inverse relationship** with the risk of coronary heart disease.

Practice by Chapter

Lipid Classification and Chemistry

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Fatty Acid Oxidation

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Ketone Body Metabolism

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Fatty Acid Synthesis

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Metabolism of Triacylglycerols

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Phospholipid Metabolism

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Cholesterol Metabolism and Biosynthesis

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Bile Acids and Bile Salts

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Lipoprotein Metabolism and Transport

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Dyslipidemias and Atherosclerosis

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Prostaglandins and Eicosanoids

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Fatty Liver and Lipotropic Factors

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