Lipids: physiology and lipoproteins

10 ASCP MLS practice questions on Lipids: physiology and lipoproteins, part of Chemistry. The first 10 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Hard

   A 6-year-old has recurrent abdominal pain and eruptive xanthomas. Fasting triglyceride is 2,800 mg/dL (31.6 mmol/L), and refrigerated plasma has a creamy layer over a clear lower layer. The patient's post-heparin plasma hydrolyzes triglyceride normally only after normal serum is added to the assay. Which defect is most likely?

   1. ALipoprotein lipase deficiency
   2. BApo C-II deficiency
   3. CApo E2 homozygosity
   4. DLDL receptor deficiency

   Show answerHide answer

   Answer: B · Apo C-II deficiency

   A creamy layer over a clear lower layer shows chylomicrons alone, the type I pattern of familial chylomicronemia. Heparin releases lipoprotein lipase into plasma, so its activity can be tested. Here the enzyme is present but works only when normal serum supplies the missing activator, apo C-II. In lipoprotein lipase deficiency, adding normal serum would not restore activity, because the enzyme itself is missing.

   • A: Normal serum would not restore activity in lipoprotein lipase deficiency, because the enzyme is missing.
   • C: Apo E2 homozygosity causes remnant build-up with a broad beta band, not chylomicronemia in childhood.
   • D: LDL receptor deficiency raises LDL cholesterol, not chylomicrons.

2. Question 2 · Medium

   Chylomicron remnants are cleared by the liver mainly through receptor recognition of:

   1. AApo A-I
   2. BApo C-II
   3. CApo B-48
   4. DApo E

   Show answerHide answer

   Answer: D · Apo E

   After lipoprotein lipase removes most of their triglyceride, chylomicron remnants are taken up by liver receptors (the LDL receptor and LDL receptor-related protein) that bind apo E. Apo B-48 lacks the receptor-binding region of apo B-100, so it cannot do this. People with two copies of the poorly binding apo E2 isoform clear remnants slowly. Remnants then build up in the blood.

   • A: Apo A-I is the main protein of HDL.
   • B: Apo C-II activates lipoprotein lipase and is lost as remnants form.
   • C: Apo B-48 lacks the receptor-binding region found in apo B-100.

3. Question 3 · Easy

   Each LDL particle carries exactly one molecule of which apolipoprotein?

   1. AApo B-48
   2. BApo B-100
   3. CApo A-I
   4. DApo E

   Show answerHide answer

   Answer: B · Apo B-100

   Apo B-100 is made in the liver and stays with the particle as VLDL is converted to IDL and then LDL, one molecule per particle. It is the ligand that the LDL receptor recognizes. Because each atherogenic particle carries one apo B, the apo B level reflects the number of these particles. Apo B-48 is the shorter intestinal form found on chylomicrons.

   • A: Apo B-48 is the intestinal form found on chylomicrons and their remnants.
   • C: Apo A-I is the main protein of HDL.
   • D: Apo E is found on VLDL, IDL, remnants and HDL, and LDL carries little of it.

4. Question 4 · Easy

   Triglyceride made in the liver is released into the blood mainly as part of:

   1. AHDL
   2. BVLDL
   3. CLDL
   4. DChylomicrons

   Show answerHide answer

   Answer: B · VLDL

   The liver packages endogenous triglyceride with apo B-100 into very-low-density lipoprotein (VLDL). Lipoprotein lipase removes triglyceride from VLDL, turning it into IDL and then LDL. Excess VLDL makes fasting plasma evenly turbid without a creamy top layer. VLDL migrates in the pre-beta position on lipoprotein electrophoresis.

   • A: HDL carries little triglyceride.
   • C: LDL is formed from VLDL and is rich in cholesterol, not triglyceride.
   • D: Chylomicrons carry dietary triglyceride from the intestine.

5. Question 5 · Medium

   Cholesteryl ester transfer protein (CETP) moves cholesteryl ester from HDL to VLDL and LDL in exchange for:

   1. AApo A-I
   2. BFree cholesterol
   3. CPhospholipid
   4. DTriglyceride

   Show answerHide answer

   Answer: D · Triglyceride

   CETP swaps cholesteryl ester from HDL for triglyceride from apo B-containing lipoproteins. When triglyceride-rich VLDL is high, more exchange occurs, and the triglyceride-loaded HDL is then broken down faster by hepatic lipase. This is one reason high triglycerides go with low HDL cholesterol. Phospholipid is moved by a separate protein, PLTP.

   • A: CETP moves lipids, not apolipoproteins.
   • B: Free cholesterol is esterified on HDL by LCAT, not exchanged by CETP.
   • C: Phospholipid is moved by phospholipid transfer protein (PLTP), not CETP.

6. Question 6 · Easy

   Which apolipoprotein must be present on a chylomicron or VLDL particle for lipoprotein lipase to hydrolyze its triglyceride?

   1. AApo C-II
   2. BApo B-48
   3. CApo A-I
   4. DApo C-III

   Answer and explanation in LearnFree account

7. Question 7 · Easy

   Lecithin-cholesterol acyltransferase (LCAT), which esterifies free cholesterol on HDL, is activated mainly by:

   1. AApo A-I
   2. BApo E
   3. CApo B-100
   4. DApo C-II

   Answer and explanation in LearnFree account

8. Question 8 · Easy

   Which lipoprotein class carries triglyceride absorbed from a fatty meal from the intestine into the blood?

   1. ALDL
   2. BVLDL
   3. CHDL
   4. DChylomicrons

   Answer and explanation in LearnFree account

9. Question 9 · Easy

   Lipoprotein(a) is an LDL-like particle in which apo B-100 is linked by a disulfide bond to apo(a). Apo(a) is structurally similar to:

   1. APlasminogen
   2. BAntithrombin
   3. CAlbumin
   4. DFibrinogen

   Answer and explanation in LearnFree account

10. Question 10 · Medium

    In reverse cholesterol transport, free cholesterol leaves peripheral cells through the ABCA1 transporter. It is first accepted by:

    1. AChylomicron remnants
    2. BCirculating VLDL
    3. CLipid-poor apo A-I
    4. DLDL particles

    Answer and explanation in LearnFree account