Lipid Metabolism — MCQs

Lipid Metabolism Indian Medical PG Practice Questions and MCQs

Question 591: Which one of the following oil/fat contains high mono-unsaturated fatty acid and moderate linoleic acid?

A. Flax seed oil
B. Palm kernel oil
C. Groundnut oil (Correct Answer)
D. Safflower oil

Explanation: ***Groundnut oil*** - Groundnut oil, also known as peanut oil, is rich in **monounsaturated fatty acids (MUFAs)**, particularly **oleic acid**, which can constitute 40-60% of its fat content. - It also contains a moderate amount of **linoleic acid (LA)**, an omega-6 polyunsaturated fatty acid, typically around 20-30%. *Flax seed oil* - Flax seed oil is known for its exceptionally high content of **alpha-linolenic acid (ALA)**, an omega-3 fatty acid, making it predominantly polyunsaturated. - While it contains some MUFAs and LA, their proportions are significantly lower than in groundnut oil. *Palm kernel oil* - Palm kernel oil is characterized by a very high content of **saturated fatty acids**, especially **lauric acid**, making it solid at room temperature. - It contains very low levels of both monounsaturated and polyunsaturated fatty acids like linoleic acid. *Safflower oil* - Safflower oil is available in two main types: high-linoleic and high-oleic. Traditional safflower oil is extremely high in **linoleic acid** (up to 75%), while high-oleic varieties are very high in **oleic acid** (up to 80%). - It does not contain a moderate amount of linoleic acid alongside high MUFAs in the specific balance described for groundnut oil, as the high-linoleic type has very low MUFAs, and the high-oleic type has low linoleic acid.

Question 592: Cyclooxygenase plays a role in which pathway?

A. Leukotriene
B. Vitamin K
C. Krebs cycle
D. Prostaglandin (Correct Answer)

Explanation: ***Prostaglandin*** - **Cyclooxygenase (COX)** enzymes specifically catalyze the conversion of **arachidonic acid** into **prostaglandins**, **prostacyclins**, and **thromboxanes**. - This pathway is crucial for mediating **inflammation**, **fever**, and **pain** responses in the body. *Leukotriene* - **Leukotrienes** are synthesized via the **lipoxygenase** pathway, not the cyclooxygenase pathway. - They are primarily involved in **allergic reactions** and **asthma**, causing bronchoconstriction and increased vascular permeability. *Vitamin K* - **Vitamin K** is a fat-soluble vitamin essential for the synthesis of **blood clotting factors** and does not involve cyclooxygenase enzymes. - It acts as a cofactor for the enzyme **gamma-glutamyl carboxylase**. *Krebs cycle* - The **Krebs cycle (citric acid cycle)** is a central metabolic pathway for **cellular respiration**, producing ATP, NADH, and FADH2. - It takes place in the **mitochondria** and is involved in the breakdown of carbohydrates, fats, and proteins for energy, unrelated to cyclooxygenase.

Question 593: Liver produces ketones but cannot use it due to the deficiency of which of the following enzyme?

A. Alkaline phosphatase
B. Alanine transaminase
C. Thiophorase (Correct Answer)
D. Thiolase

Explanation: ***Thiophorase*** - The liver lacks **thiophorase (succinyl-CoA:3-ketoacid CoA transferase)**, which is crucial for converting **acetoacetate** to **acetoacetyl-CoA**. - This enzyme deficiency prevents the liver from utilizing ketones as an energy source, even though it is a primary site for their production. *Alkaline phosphatase* - **Alkaline phosphatase** is a non-specific enzyme found in various tissues, including bone, liver, and intestine. - Its primary role is to **hydrolyze phosphate esters**, and it is not directly involved in ketone metabolism. *Alanine transaminase* - **Alanine transaminase (ALT)** is a liver enzyme primarily involved in **amino acid metabolism**, specifically in the transfer of an amino group from alanine to α-ketoglutarate. - It plays no direct role in the synthesis or utilization of ketone bodies. *Thiolase* - **Thiolase** is an enzyme involved in both the synthesis and breakdown of ketone bodies. - It converts **two acetyl-CoA molecules into acetoacetyl-CoA** during ketogenesis and also cleaves acetoacetyl-CoA into two acetyl-CoA molecules during ketolysis in extrahepatic tissues.

Question 594: BARTH syndrome is caused by deficiency of?

A. Glycolipids
B. Sphingomyelin
C. Cardiolipin (Correct Answer)
D. Cerebroside

Explanation: ***Cardiolipin*** - **BARTH syndrome** is a rare, X-linked genetic disorder caused by mutations in the **TAZ gene**, which encodes for the enzyme **tafazzin**. - **Tafazzin** is crucial for the remodeling of **cardiolipin**, a phospholipid essential for mitochondrial membrane integrity and function. Deficiency of properly remodeled (mature) cardiolipin leads to the characteristic cardiomyopathy, skeletal myopathy, neutropenia, and growth delay seen in BARTH syndrome. *Glycolipids* - **Glycolipids** are lipids with a carbohydrate attached, important for cell recognition and signaling. - Their deficiency or abnormal metabolism is associated with conditions like **glycosphingolipidoses** (e.g., Gaucher disease, Fabry disease), not BARTH syndrome. *Sphingomyelin* - **Sphingomyelin** is a type of sphingolipid found in animal cell membranes, particularly in the myelin sheath. - Its deficiency or accumulation is linked to **Niemann-Pick disease**, which presents with hepatosplenomegaly and neurodegeneration, distinct from BARTH syndrome. *Cerebroside* - **Cerebrosides** are a type of glycosphingolipid found in the myelin sheath and nerve cell membranes. - Disorders involving cerebroside metabolism include **Krabbe disease** (globoid cell leukodystrophy) and **Gaucher disease**, which are pathologically distinct from BARTH syndrome.

Question 595: Energy reserve of the body is:

A. Fibres
B. Triglyceride (Correct Answer)
C. Carbohydrate
D. Proteins

Explanation: ***Triglyceride*** - **Triglycerides** are the primary form of **energy storage** in the body, stored predominantly in **adipose tissue**. - They provide a highly concentrated and long-term energy reserve, crucial for periods of fasting or increased energy demand. *Fibres* - **Dietary fibers** are indigestible plant-derived carbohydrates that contribute to digestive health but do not serve as a direct energy reserve for the body. - They are important for maintaining gut motility and regulating blood sugar, but are not metabolized for energy. *Carbohydrate* - **Carbohydrates** (primarily **glycogen**) serve as the **body's most immediate energy source**, stored in the liver and muscles. - However, glycogen stores are limited and are depleted much faster than triglyceride stores during prolonged energy needs. *Proteins* - **Proteins** have numerous structural and functional roles in the body, but are typically used for energy only in cases of **prolonged starvation** when carbohydrate and fat reserves are severely depleted. - Their primary function is not energy storage, and their breakdown for energy can lead to **muscle wasting** and compromise essential body functions.

Question 596: Which of the following is cardio protective?

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

Explanation: ***HDL*** - **High-density lipoprotein (HDL)** is known as "good cholesterol" because it helps remove **excess cholesterol** from the body and transport it back to the liver for excretion. - This process, called **reverse cholesterol transport**, helps prevent the buildup of plaque in arteries, thereby reducing the risk of **atherosclerosis** and cardiovascular disease. *CHYLOMICRON* - **Chylomicrons** are responsible for transporting **dietary triglycerides** from the intestines to various tissues. - While essential for nutrient absorption, elevated chylomicron levels can contribute to **hypertriglyceridemia**, which is a risk factor for cardiovascular disease and pancreatitis. *VLDL* - **Very low-density lipoprotein (VLDL)** primarily transports **endogenously synthesized triglycerides** from the liver to peripheral tissues. - High levels of VLDL are considered a **risk factor for atherosclerosis** as they can be metabolized into LDL, contributing to plaque formation. *LDL* - **Low-density lipoprotein (LDL)** is often referred to as "bad cholesterol" because it deposits cholesterol in the walls of arteries. - This deposition leads to the formation of **atherosclerotic plaque**, which can narrow arteries and increase the risk of heart attacks and strokes.

Question 597: Essential fatty acid:

A. Citric acid
B. Palmitic acid
C. Linoleic acid (Correct Answer)
D. Stearic acid

Explanation: ***Linoleic acid*** - **Linoleic acid** is an **omega-6 fatty acid** that is considered essential because the human body cannot synthesize it and must obtain it through diet. - It is a precursor for other important fatty acids like **arachidonic acid**, which are involved in inflammation and blood clotting. *Citric acid* - **Citric acid** is an organic acid found in citrus fruits and is a key intermediate in the **Krebs cycle** (citric acid cycle), a central metabolic pathway, but it is not a fatty acid. - It is readily synthesized by the body and is therefore not considered an essential nutrient. *Palmitic acid* - **Palmitic acid** is a **saturated fatty acid** with 16 carbon atoms, which is the most common fatty acid in animals and plants. - It can be synthesized by the human body from excess carbohydrates and proteins, hence it is not an essential fatty acid. *Stearic acid* - **Stearic acid** is another common **saturated fatty acid** with 18 carbon atoms, found in various animal and plant fats. - Like palmitic acid, it can be endogenously synthesized by the body and is not considered essential.

Question 598: Colipase is found in?

A. Pancreatic juice (Correct Answer)
B. Saliva
C. Bile
D. Succus entericus

Explanation: ***Pancreatic juice*** - **Colipase** is a co-enzyme secreted by the **pancreas** that is essential for the activity of pancreatic lipase. - It helps **pancreatic lipase** anchor to the surface of fat globules, preventing its inactivation by bile salts and facilitating fat digestion. *Saliva* - Saliva primarily contains **alpha-amylase** (ptyalin) for carbohydrate digestion and **lingual lipase** for initial fat digestion. - It does not contain colipase. *Bile* - **Bile** is produced by the liver and stored in the gallbladder, primarily aiding in fat emulsification. - It contains **bile salts**, cholesterol, bilirubin, and phospholipids but not digestive enzymes like colipase. *Succus entericus* - **Succus entericus**, or intestinal juice, is secreted by the small intestine and contains enzymes like **sucrase**, **maltase**, **lactase**, and peptidases. - It does not contain colipase, which is specifically a pancreatic enzyme.

Question 599: Apoprotein for chylomicron remnants:

A. Apo A2
B. Apo E (Correct Answer)
C. Apo C1
D. Apo A1

Explanation: ***Apo E*** - **Apolipoprotein E** (**Apo E**) is crucial for the uptake of **chylomicron remnants** and **VLDL remnants** (IDL) by the liver via the **LDL receptor-related protein 1 (LRP1)**. - It acts as a **ligand** for this receptor, facilitating the clearance of dietary fats from the circulation. *Apo A2* - **Apo A2** is a primary apolipoprotein of **high-density lipoprotein (HDL)**, not chylomicron remnants. - Its exact function is not fully understood, but it may modulate the activity of **hepatic lipase**. *Apo C1* - **Apo C1** is found on **chylomicrons**, **VLDL**, and **HDL**, but it is not the primary apoprotein responsible for the uptake of chylomicron remnants by the liver. - It is known to **activate lecithin-cholesterol acyltransferase (LCAT)** and may inhibit **cholesterol ester transfer protein (CETP)**. *Apo A1* - **Apo A1** is the most abundant apolipoprotein in **HDL** and is essential for its structure and function. - It is a potent **activator of LCAT**, an enzyme that esterifies cholesterol in HDL, which is key for **reverse cholesterol transport**.

Question 600: Pregnenolone is not in the biosynthetic pathway of which substance?

A. Cortisol
B. DHEA
C. Estrogen
D. 1,25(OH)2D (Correct Answer)

Explanation: ***1,25(OH)2D*** - **1,25-dihydroxyvitamin D (Calcitriol)** is the active form of **vitamin D**, synthesized from **cholesterol** in a pathway involving the skin, liver, and kidneys, not directly from pregnenolone. - Its synthesis begins with 7-dehydrocholesterol in the skin, which is converted to **cholecalciferol** by UV light, then hydroxylated in the liver and kidneys. *Cortisol* - **Pregnenolone** is a direct precursor in the synthesis of **cortisol**, as it is converted to progesterone, which then proceeds through various hydroxylations to form cortisol. - The adrenal cortex enzymes convert pregnenolone through a series of steps to produce **glucocorticoids** like cortisol. *DHEA* - **Dehydroepiandrosterone (DHEA)** is synthesized directly from **pregnenolone** by the enzyme 17α-hydroxylase/17,20-lyase (CYP17A1). - Pregnenolone is the initial steroid intermediate that can be shunted towards androgen synthesis, bypassing progesterone. *Estrogen* - **Estrogen** synthesis involves **pregnenolone** as a precursor, which is converted to **DHEA** and then to androstenedione, which is aromatized to estrone and subsequently estradiol. - The pathway from pregnenolone involves multiple steps including the formation of **androgens** as intermediates, which are then converted to estrogens.

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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