Updated: 8/21/2018

Apolipoproteins

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Overview
 

 
Snapshot
  • A 50-year-old woman presents to her primary care physician for a regular checkup.  She states that for the past four months she has not experienced menses.  Her primary care physician suspects that she has gone through menopause.  On routine lab work, her LDL has increased as compared to one year ago, and her HDL has decreased drastically.
Introduction
  • Mechanisms for fatty acid and cholesterol transport
  • Different types that vary by
    • density
      • most dense
        • HDL (high density)
        • LDL (low density)
        • IDL (intermediate density)
        • VLDL (very low density)
        • chylomicrons
      • least dense
    • types of apolipoprotein

 

HDL
  • Function
    • transfer cholesterol
      • tissues → liver
    • good cholesterol
  • Structure
    • apoA-1
      • activates lecithin cholesterol acyltransferase (LCAT)
    • apoE/apoC-II 
      • apolipoproteins donated to chylomicrons and VLDL
LDL
  • Function
    • transfer cholesterol
      • liver → tissues
        • most recycles back to be absorbed by the liver
    • bad cholesterol
  • Structure
    • apoB-100 
      • mediates endocytosis of LDL by binding to apoB-100 (LDL) receptor on liver and tissues
IDL
  • Function
    • VLDL → IDL + TGs
    • picks up cholesterol esters from HDL
      • catalyzed by cholesterol ester transfer protein (CETP)
      • IDL + cholesterol from HDL → LDL
  • Structure
    • apoE
      • recieves from HDL
      • mediates uptake by the liver
      • remember: apoE empties to liver
    • apoB-100
      • mediates endocytosis of LDL by binding to apoB-100 (LDL) receptor on liver and tissues
VLDL
  • Function
    • transports TGs
      • liver → tissues
  • Structure 
    • apoB-100
      • form packaged and secreted from liver
    • apoC-II
      • activates lipoprotein lipase
        • catalyzes hydrolysis of triglycerides into individual FAs for absorbtion
        • ↑ regulated by insulin
    • apoE
      • mediates uptake by the liver
Chylomicrons
  • Function
    • transport cholesterol, TGs, FAs, and fat soluble vitamins
      • intestine → tissues
    • released from intestinal lumen cells into lymphatics
  • Structure
    • apo-48
      • form packaged and secreted by intestine
    • apoC-II
      • activates lipoprotein lipase
      • added from HDL
    • apoE
      • mediates uptake by the liver
      • added from HDL

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Questions (2)
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(M1.BC.17.4768) A 60-year-old patient is at his physician’s office for a routine health maintenance exam. The patient has a past medical history of osteoarthritis in his right knee and GERD that is well-controlled with over the counter medication. On a fasting lipid profile, he is found to have high cholesterol. The patient is started on daily atorvastatin to reduce his risk of cardiovascular disease. What is the major apolipoprotein found on the lipoprotein most directly affected by his statin medication? Tested Concept

QID: 109077
1

Apolipoprotein A-I

4%

(5/116)

2

Apolipoprotein B-48

14%

(16/116)

3

Apolipoprotein B-100

54%

(63/116)

4

Apolipoprotein C-II

13%

(15/116)

5

Apolipoprotein E

12%

(14/116)

M 3 C

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