CLS Lipid Metabolism & Physiology 3 — Questions and Answers
Question 1: Which dietary fatty acid class is most effective at raising LDL cholesterol levels?
- Monounsaturated fatty acids (MUFA)
- Omega-3 polyunsaturated fatty acids
- Trans fatty acids (Correct answer)
- Short-chain saturated fatty acids
Correct answer: Trans fatty acids
Trans fatty acids both raise LDL-C and lower HDL-C, making them uniquely atherogenic compared to saturated fats which raise both LDL and HDL.
Question 2: Lp(a) is formed when LDL binds covalently to which protein?
- ApoC-III
- Apolipoprotein(a) (Correct answer)
- Fibrinogen
- ApoE
Correct answer: Apolipoprotein(a)
Lp(a) is formed by a disulfide bond between ApoB-100 on LDL and apolipoprotein(a), which structurally resembles plasminogen and may promote thrombosis and atherosclerosis.
Question 3: Which enzyme esterifies free cholesterol within HDL particles to form cholesteryl esters?
- CETP
- Hepatic lipase
- LCAT (Correct answer)
- Phospholipid transfer protein
Correct answer: LCAT
Lecithin-cholesterol acyltransferase (LCAT) is activated by ApoA-I and esterifies free cholesterol in HDL, trapping it in the particle core and driving cholesterol efflux from tissues.
Question 4: A patient with type III hyperlipidemia (dysbetalipoproteinemia) has excess accumulation of which lipoprotein remnants?
- LDL and Lp(a)
- VLDL remnants (IDL) and chylomicron remnants (Correct answer)
- HDL2 and HDL3
- Lp(a) and nascent HDL
Correct answer: VLDL remnants (IDL) and chylomicron remnants
Type III hyperlipidemia (familial dysbetalipoproteinemia) results from ApoE2 homozygosity, which impairs hepatic clearance of IDL and chylomicron remnants, causing equal elevations of cholesterol and triglycerides.
Question 5: In the exogenous lipid pathway, chylomicrons are assembled in which cells?
- Hepatocytes
- Intestinal enterocytes (Correct answer)
- Vascular endothelial cells
- Adipocytes
Correct answer: Intestinal enterocytes
Chylomicrons are synthesized in intestinal enterocytes from dietary lipids and secreted into lymphatic lacteals before entering the circulation via the thoracic duct.
Question 6: Which receptor mediates hepatic uptake of LDL particles through endocytosis?
- SR-BI
- PCSK9
- LDL receptor (LDLR) (Correct answer)
- CD36
Correct answer: LDL receptor (LDLR)
The LDL receptor (LDLR) recognizes ApoB-100 on LDL and mediates its uptake into hepatocytes via clathrin-coated pit endocytosis, where the receptor is recycled.
Question 7: Omega-3 fatty acids (EPA and DHA) primarily lower which lipid parameter?
- LDL-C
- Lp(a)
- Triglycerides (Correct answer)
- Total cholesterol
Correct answer: Triglycerides
High-dose omega-3 fatty acids reduce hepatic VLDL triglyceride synthesis and increase triglyceride clearance, lowering serum triglycerides by 20-50% at therapeutic doses (4 g/day).
CLS Lipid Metabolism & Physiology 3
Which dietary fatty acid class is most effective at raising LDL cholesterol levels?