Lipid Metabolism Practice Questions

Q: Which lipid is primarily elevated in poorly controlled diabetes mellitus?

Triglycerides. ***Triglycerides*** - In poorly controlled **diabetes mellitus**, insulin deficiency or resistance leads to increased hepatic synthesis of **triglycerides** and impaired clearance from the bloodstream. - This often results in **hypertriglyceridemia**, a common dyslipidemia in diabetic patients, contributing to increased cardiovascular risk. *HDL* - **High-density lipoprotein (HDL)** levels are typically **decreased** in poorly controlled diabetes due to increased catabolism and reduced synthesis. - Low HDL is considered an independent risk factor for **atherosclerosis** and is a common finding in diabetic dyslipidemia. *VLDL* - While **Very Low-Density Lipoprotein (VLDL)** levels may be elevated in diabetes, this is primarily due to increased synthesis and secretion of **triglyceride-rich VLDL** particles from the liver. - Therefore, the elevation in **VLDL** is a consequence of the underlying **hypertriglyceridemia**. *Cholesterol* - **Total cholesterol** levels can be elevated in poorly controlled diabetes, but this is often a consequence of an increase in **LDL cholesterol** and **triglycerides**. - **Total cholesterol** itself is not the primary lipid that is directly elevated as a first-order effect of the metabolic derangement.

Q: What is the primary apolipoprotein deficiency associated with broad beta disease (familial type III hyperlipoproteinemia)?

Apo E. ***Apo E*** - **Familial type III hyperlipoproteinemia**, also known as broad beta disease or dysbetalipoproteinemia, is primarily caused by homozygosity for the **ApoE2 allele**. - ApoE2 has **defective binding** to lipoprotein receptors, leading to impaired clearance of chylomicron and VLDL remnants. *Apo A* - Apo A-I is the main apolipoprotein of **HDL** and plays a crucial role in **reverse cholesterol transport**. - Deficiencies in Apo A-I are typically associated with conditions like **Tangier disease** or familial HDL deficiency, not type III hyperlipoproteinemia. *Apo B* - Apo B-100 is a key structural protein for **LDL** and VLDL, while Apo B-48 is essential for **chylomicrons**. - Defects in Apo B are associated with conditions like **familial hypercholesterolemia** (Apo B-100) or abetalipoproteinemia (Apo B-48), not primarily type III hyperlipoproteinemia. *Apo C* - Apo C-II is an activator of **lipoprotein lipase**, important for triglyceride hydrolysis. - Deficiencies in Apo C-II lead to **severe hypertriglyceridemia** (type I hyperlipoproteinemia), not directly broad beta disease.

Q: What is the major apolipoprotein of chylomicrons?

B-48. ***B-48*** - **Apolipoprotein B-48** is exclusively produced in the intestine and is the **major structural apolipoprotein** found only on **chylomicrons**. - It is critical for the **assembly and secretion of chylomicrons** from intestinal cells into the lymphatic system. - ApoB-48 represents the N-terminal 48% of ApoB-100 and lacks the LDL receptor-binding domain. *B-100* - **Apolipoprotein B-100** is synthesized in the liver and is the primary structural apolipoprotein of **VLDL, IDL, and LDL**. - It acts as the **ligand for the LDL receptor**, facilitating the uptake of cholesterol into cells. *Apo-C* - **Apolipoprotein C (Apo-C)** proteins (e.g., ApoC-II, ApoC-III) are exchangeable apolipoproteins found on several lipoproteins, including chylomicrons, VLDL, and HDL. - **ApoC-II activates lipoprotein lipase**, which hydrolyzes triglycerides, but these are **not structural proteins** and are present in smaller quantities. *Apo-E* - **Apolipoprotein E (Apo-E)** is acquired by chylomicrons in circulation and is important for **chylomicron remnant clearance** by the liver. - While present on chylomicrons, it is **not the major structural apolipoprotein** – that role belongs to ApoB-48.

Q: Which of the following is the MOST accurate statement regarding thromboxane A2?

Prothrombogenic. ***ABCD*** - Thromboxane A2 is primarily **formed by platelets** [1] and is derived from **PGG2/PGH2**, having a significant role in **hemostasis**. - It is known to be **prothrombogenic** [1] and acts as a **vasoconstrictor** [2], enhancing platelet aggregation and promoting localized increases in **vascular resistance**. *ACB* - This option indicates only a partial representation of thromboxane A2's functions and formation. - It misses the comprehensive list of effects and does not mention it as a **vasoconstrictor** or its role in hemostasis. *ABC* - Like , it lacks recognition of all relevant characteristics of thromboxane A2. - Thus, it omits the **vasodilator** function, even though thromboxane A2 acts mainly as a **vasoconstrictor**. *ABCDE* - Including **E as vasodilator** contradicts the well-known actions of thromboxane A2, which does not promote vasodilation [2]. - Thus, this ssentially misrepresents thromboxane A2 as it primarily promotes **vasoconstriction** and is **prothrombogenic**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Hemodynamic Disorders, Thromboembolic Disease, and Shock, p. 130. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 95-96.

Q: Which of the following is most strongly associated with heart disease?

LDL. ***LDL*** - **Low-density lipoprotein (LDL)** is often referred to as "bad cholesterol" because high levels contribute to the buildup of **plaque** in the arteries, leading to **atherosclerosis** and increasing the risk of heart disease. - **Elevated LDL** promotes cholesterol deposition in arterial walls, narrowing the vessels and impeding blood flow. *HDL* - **High-density lipoprotein (HDL)** is known as "good cholesterol" as it helps remove cholesterol from the arteries and transport it back to the liver for excretion. - **High HDL levels** are generally protective against heart disease, not associated with its development. *VLDL* - **Very-low-density lipoprotein (VLDL)** primarily transports **triglycerides** synthesized in the liver to various tissues. - While high VLDL levels can increase the risk of heart disease, primarily due to their breakdown into LDL, **LDL itself is a more direct and stronger predictor** of atherosclerotic disease. *Chylomicrons* - **Chylomicrons** are responsible for transporting **dietary fats** (triglycerides and cholesterol) from the intestines to the rest of the body after a meal. - Although high levels of chylomicrons can be associated with increased triglyceride levels, they are typically present for only a few hours after eating and are **not as strongly implicated in chronic atherosclerosis** as LDL.

Q: Which of the following statements is NOT true about medium chain acyl-CoA dehydrogenase deficiency?

Cardiomyopathy. ***Cardiomyopathy*** - While other fatty acid oxidation disorders can present with **cardiomyopathy**, Medium Acyl-CoA Dehydrogenase Deficiency (MCADD) primarily affects the **liver** and **skeletal muscle**, not the heart. - The classic presentation involves episodes of **hypoketotic hypoglycemia** and **lethargy**, often triggered by fasting or illness. *Autosomal recessive inheritance* - MCADD is indeed inherited in an **autosomal recessive pattern**, meaning an individual must inherit two copies of the mutated gene (one from each parent) to be affected. - This is a characteristic feature of many **inborn errors of metabolism**, including fatty acid oxidation disorders. *Hypoketotic hypoglycemia* - This is a hallmark feature of MCADD, as the body cannot effectively break down **medium-chain fatty acids** into ketones for energy during periods of fasting. - The buildup of toxic intermediates and lack of ketosis contribute to the acute metabolic crises observed in affected individuals. *Episodes associated with fasting* - Fasting is a common trigger for metabolic decompensation in MCADD, as the body becomes reliant on **fatty acid oxidation** for energy when glucose stores are depleted. - Illnesses that reduce appetite or increase energy demands, leading to prolonged fasting, can precipitate acute crises.

Question 1

Which lipid is primarily elevated in poorly controlled diabetes mellitus?

Accepted Answer

Triglycerides

Answer

HDL

Answer

Cholesterol

Answer

VLDL

Question 2

What is the primary apolipoprotein deficiency associated with broad beta disease (familial type III hyperlipoproteinemia)?

Accepted Answer

Apo E

Answer

Apo A

Answer

Apo B

Answer

Apo C

Question 3

All are true about beta-oxidation except:

Accepted Answer

Carnitine palmitoyl transferase I is present in mitochondrial matrix.

Answer

Activation of FA is a must

Answer

Carnitine palmitoyl transferase I is present in outer mitochondrial membrane

Answer

Carnitine palmitoyl transferase II is present in inner mitochondrial membrane

Question 4

What is the major apolipoprotein of chylomicrons?

Accepted Answer

B-48

Answer

B-100

Answer

Apo-C

Answer

Apo-E

Question 5

Which of the following is the MOST accurate statement regarding thromboxane A2?

Accepted Answer

Prothrombogenic

Answer

Formed by platelets

Answer

Formed from PGG2/PGH2

Answer

Vasoconstrictor

Question 6

Which of the following is most strongly associated with heart disease?

Accepted Answer

LDL

Answer

HDL

Answer

VLDL

Answer

Chylomicrons

Question 7

Which of the following statements is NOT true about medium chain acyl-CoA dehydrogenase deficiency?

Accepted Answer

Cardiomyopathy

Answer

Autosomal recessive inheritance

Answer

Hypoketotic hypoglycemia

Answer

Episodes associated with fasting

Lipid Metabolism — MCQs

Lipid Metabolism — MCQs

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