Lipid Metabolism Practice Questions

Q: Krabbe's disease is due to deficiency of ?

Beta galactocerebrosidase. ***Beta galactocerebrosidase*** - Krabbe's disease is specifically caused by a deficiency of **beta-galactocerebrosidase**, leading to the accumulation of toxic substances in the brain [1]. - This disease predominantly affects the **myelin sheath**, resulting in severe neurological deterioration [1]. *Arylsulfatase* - Deficiency of **arylsulfatase** is associated with **metachromatic leukodystrophy**, not Krabbe's disease. - Symptoms and pathology differ significantly, primarily affecting **sulfatides** rather than galactocerebrosides. *Sphingomyelinase* - A deficiency of **sphingomyelinase** is linked to **Niemann-Pick disease**, characterized by splenomegaly and liver involvement. - This condition does not involve the same neurological deterioration seen in Krabbe's disease. *Hexosaminidase* - Hexosaminidase deficiency is associated with **Tay-Sachs disease**, primarily affecting the **GM2 gangliosides** [2]. - This results in different clinical manifestations, such as **cherry-red spots** and progressive neurodegeneration, rather than the symptoms of Krabbe's disease [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1304-1305. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, p. 161.

Q: Which of the following statements about ketone bodies is false?

HMG CoA reductase is the rate-limiting enzyme. ***HMG CoA reductase is the rate-limiting enzyme*** - This statement is **false** because **HMG-CoA synthase**, not HMG-CoA reductase, is the **rate-limiting enzyme in ketogenesis**. - **HMG-CoA reductase** is the rate-limiting enzyme in **cholesterol synthesis**, a completely different metabolic pathway. *Acetoacetate is primary ketone body* - **Acetoacetate** is indeed considered the **primary ketone body**, as **β-hydroxybutyrate** is derived from it and **acetone** is a spontaneous breakdown product of acetoacetate. - It is the first ketone body formed during the synthesis pathway. *Synthesized in mitochondria* - Ketone bodies are synthesized in the **mitochondrial matrix** of liver cells. - This location allows for the efficient use of **acetyl-CoA** generated from fatty acid oxidation. *Synthesized in liver* - The liver is the **primary site of ketogenesis**, where fatty acids are converted into ketone bodies. - This process is crucial for providing alternative fuel to extrahepatic tissues during periods of fasting or prolonged starvation.

Q: Ketone bodies are not used by?

RBC. ***RBC*** - Red blood cells **lack mitochondria**, which are essential organelles for the **oxidation of ketone bodies** (acetoacetate and β-hydroxybutyrate) for energy production. - Their primary energy source is **anaerobic glycolysis** of glucose. *Muscle* - **Skeletal and cardiac muscles** readily utilize **ketone bodies** as an alternative fuel source, especially during prolonged fasting or starvation. - This helps to conserve glucose for other tissues, particularly the brain. *Brain* - The brain can adapt to use **ketone bodies** for energy when glucose supply is limited, such as during prolonged fasting or in cases of uncontrolled diabetes. - This process is crucial for brain function when glucose levels are low. *Renal cortex* - The **renal cortex** is capable of utilizing **ketone bodies** for energy, particularly during starvation. - The kidney is also involved in the **synthesis of glucose** (gluconeogenesis) and the excretion of ketone bodies.

Q: Albumin is the primary transport protein in blood for which of the following substances?

Free fatty acids (FFA). ***Free fatty acids (FFA)*** - **Albumin is the PRIMARY and MAJOR transport protein for free fatty acids** in the bloodstream, with each albumin molecule having **6-7 high-affinity binding sites** for FFAs. - This binding is essential for transporting water-insoluble fatty acids from **adipose tissue** (during lipolysis) to peripheral tissues for **β-oxidation and energy production**. - In the context of lipid metabolism, albumin-FFA transport is the **most quantitatively significant** and physiologically important binding function. - **Clinical relevance:** Impaired albumin levels directly affect FFA transport capacity. *Thyroxine* - While albumin does bind thyroid hormones, **thyroxine-binding globulin (TBG)** is the **primary carrier** (~70% of T4), followed by transthyretin (~15%). - Albumin binds only ~10-15% of circulating T4 with **low affinity**, serving as a secondary reserve. - TBG has **much higher affinity** for thyroid hormones than albumin. *Steroid* - Steroids are primarily transported by **specific binding globulins**: **corticosteroid-binding globulin (CBG)** for cortisol and **sex hormone-binding globulin (SHBG)** for testosterone/estrogen. - While albumin binds ~10-20% of steroids, it is a **secondary carrier** with lower affinity than the specific globulins. *Calcium* - Although ~40-45% of plasma calcium is albumin-bound (important for calcium homeostasis), this is a **passive binding function** rather than active transport. - Albumin's role with calcium is primarily **buffering** rather than the dedicated transport function it provides for FFAs. - In the context of **lipid metabolism** and **transport proteins**, FFA binding is the hallmark function of albumin.

Q: What is essential for the transfer of fatty acid across the mitochondrial membrane?

Carnitine. ***Carnitine*** - **Carnitine** is crucial for transporting **long-chain fatty acids** into the mitochondrial matrix for **beta-oxidation**. - It forms **acylcarnitine** by esterifying with fatty acids, allowing passage through the inner mitochondrial membrane via the **carnitine-acylcarnitine translocase**. *Creatinine* - **Creatinine** is a waste product formed from the breakdown of **creatine phosphate** in muscles and is excreted by the kidneys. - It serves as a marker for **kidney function** and has no role in fatty acid transport. *Biotin* - **Biotin** is a vitamin cofactor essential for **carboxylase enzymes**, including acetyl-CoA carboxylase in **fatty acid synthesis**. - While involved in lipid metabolism, it plays no role in the transport of fatty acids across mitochondrial membranes. *Creatine* - **Creatine** is a nitrogenous organic acid that helps supply energy to cells, primarily muscle, by facilitating the regeneration of **ATP**. - It plays no direct role in the facilitated transport of fatty acids across the mitochondrial membrane.

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

HDL. ***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.

Q: Primary hypercholesterolemia is:

Type IIa. ***Type Ha*** - **Primary hypercholesterolemia** specifically refers to **Familial Hypercholesterolemia**, which is classified as Type Ha due to a genetic defect affecting LDL receptor activity [1]. - It typically presents with **high cholesterol levels** and an increased risk of premature cardiovascular disease [1]. *Type I* - Type I hyperlipoproteinemia is associated with **chylomicronemia**, leading to elevated triglycerides rather than cholesterol. - Symptoms include **pancreatitis** and eruptive xanthomas, not primarily high cholesterol levels. *Type III* - Type III hyperlipoproteinemia is known as **Dysbetalipoproteinemia**, associated with **increased IDL** and can cause elevated cholesterol, but is not classified as primary hypercholesterolemia. - It typically presents with **tuberous xanthomas** and is linked to **apolipoprotein E deficiency**. *Type IIb* - Type IIb hyperlipoproteinemia involves **elevation of LDL and VLDL**, but it is not classified as primary hypercholesterolemia; it is a mixed dyslipidemia. - This type usually features **increased cholesterol** and **triglycerides**, distinguishing it from the familial form classified as Type Ha.

Q: Which oil has the highest concentration of linolenic acid?

Soyabean oil. ***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%).

Q: In which condition does serum appear milky white?

Increased Chylomicrons. ***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**

Q: Which of the following fatty acids has the maximum number of carbon atoms?

Cervonic acid. **Cervonic acid** - **Cervonic acid**, also known as **docosahexaenoic acid (DHA)**, is a long-chain omega-3 fatty acid with **22 carbon atoms** and 6 double bonds (22:6). - It is a primary structural component of the brain and retina and is the longest fatty acid among the options provided. *Oleic acid* - **Oleic acid** is a monounsaturated fatty acid with **18 carbon atoms** and one double bond (18:1). - It is a common fatty acid found in many animal fats and vegetable oils, but it has fewer carbon atoms than cervonic acid. *Linolenic acid* - **Linolenic acid** refers to two essential fatty acids: alpha-linolenic acid (ALA) and gamma-linolenic acid (GLA). Both have **18 carbon atoms**. - Alpha-linolenic acid (ALA) is an omega-3 fatty acid with 3 double bonds (18:3), while gamma-linolenic acid (GLA) is an omega-6 fatty acid with 3 double bonds (18:3), neither of which has more carbon atoms than cervonic acid. *Arachidonic acid* - **Arachidonic acid** is an omega-6 fatty acid with **20 carbon atoms** and four double bonds (20:4). - It is a precursor to eicosanoids and is longer than oleic and linolenic acids but shorter than cervonic acid.

Question 1

Krabbe's disease is due to deficiency of ?

Accepted Answer

Beta galactocerebrosidase

Answer

Sphingomyelinase

Answer

Hexosaminidase

Answer

Arylsulfatase

Question 2

Which of the following statements about ketone bodies is false?

Accepted Answer

HMG CoA reductase is the rate-limiting enzyme

Answer

Synthesized in mitochondria

Answer

Synthesized in liver

Answer

Acetoacetate is primary ketone body

Question 3

Ketone bodies are not used by?

Accepted Answer

RBC

Answer

Brain

Answer

Muscle

Answer

Renal cortex

Question 4

Albumin is the primary transport protein in blood for which of the following substances?

Accepted Answer

Free fatty acids (FFA)

Answer

Thyroxine

Answer

Steroid

Answer

Calcium

Question 5

What is essential for the transfer of fatty acid across the mitochondrial membrane?

Accepted Answer

Carnitine

Answer

Creatinine

Answer

Biotin

Answer

Creatine

Question 6

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

Accepted Answer

HDL

Answer

VLDL

Answer

LDL

Answer

None of the options

Question 7

Primary hypercholesterolemia is:

Accepted Answer

Type IIa

Answer

Type I

Answer

Type IIb

Answer

Type III

Question 8

Which oil has the highest concentration of linolenic acid?

Accepted Answer

Soyabean oil

Answer

Safflower oil

Answer

Coconut oil

Answer

Groundnut oil

Question 9

In which condition does serum appear milky white?

Accepted Answer

Increased Chylomicrons

Answer

Increased LDL

Answer

Increased HDL

Answer

Increased VLDL

Question 10

Which of the following fatty acids has the maximum number of carbon atoms?

Accepted Answer

Cervonic acid

Answer

Oleic acid

Answer

Linolenic acid

Answer

Arachidonic acid

Lipid Metabolism — MCQs

Lipid Metabolism — MCQs

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