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Lipoproteins

Lipoproteins

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LIPOPROTEIN FUNCTION
  • Solubilize cholesterol and triacylglycerol (TAG) & transport them in plasma
  • Deliver them to peripheral tissues
Triacylglycerol function
  • Energy storage
  • Membrane synthesis
Cholesterol function
  • Component of cell membranes
  • Precursor for steroid hormones and vitamin D
LIPOPROTEIN STRUCTURE
Apolipoprotein
  • On surface of lipoprotein
  • 3 functions:
i. Structure: bind and solubilize hydrophobic lipids ii. Recognition: contain signals that target lipoproteins to cells (recognized by receptors) iii. Enzymatic: activate or act as coenzymes in lipid metabolism
Single layer of phospholipids
  • Free cholesterol in layer
Hydrophobic core
  • Esterified cholesterol and TAG
CLASSES OF LIPOPROTEINS 1. Chylomicrons (fed state only)
  • Size: largest
  • Origin: intestine (dietary)
  • Composition: dietary lipids (mainly TAG)
  • Density: least dense
2. Very low density lipoprotein (VLDL)
  • Size: LDL < VLDL < chylomicron
  • Origin: liver (endogenous lipids)
  • Composition: Endogenously synthesized lipids (mainly TAG & phospholipids)
  • Density: LDL > VLDL > chylomicron
3. Low density lipoprotein (LDL)
  • Size: VLDL > LDL > HDL
  • Origin: VLDL
  • Composition: Major cholesterol carrier in body (greatest relative amount)
  • Density: VLDL < LDL < HDL
  • "Bad cholesterol" (atherosclerosis)
  • Regulates de novo cholesterol biosynthesis
4. High density lipoprotein (HDL)
  • Size: smallest
  • Origin: intestine and liver
  • Composition: picks up plasma cholesterol (released due to membrane turnover or cell death; carries less cholesterol than LDL)
  • Density: most dense (greatest % of protein)
  • Delivers cholesterol to liver for excretion (bile salts) and to tissues (steroid synthesis)
  • "Good cholesterol"
CLINICAL CORRELATION
HDL:LDL cholesterol ratio
  • Diagnostic used to determine a patient's risk for developing heart disease
  • Healthy ratio ~ 3.5
Hypercholesterolemia (high blood cholesterol)

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