Slayt 1

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Lipoproteins

• Function Transport of fat soluble substances
• Types 1) Chylomicron
• 2) VLDL
• 3) LDL
• 4) HDL

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Lipoprotein class Density (g/mL) Diameter (nm) Protein of dry wt Phospholipid Triacylglycerol of dry wt
HDL 1.063-1.21 5 15 33 29 8
LDL 1.019 1.063 18 28 25 21 4
IDL 1.006-1.019 25 - 50 18 22 31
VLDL 0.95 1.006 30 - 80 10 18 50
chylomicrons lt 0.95 100 - 500 1 - 2 7 84
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Apolipoproteins specific lipid-binding proteins
that attach to the surface intracellular
recognition for exocytosis of the nascent
particle after synthesis activation of
lipid-processing enzymes in the bloodstream,
binding to cell surface receptors for
endocytosis and clearance. Main lipid
components triacylglycerols, cholesterol esters,
phospholipids. Major lipoproteins
chylomicrons very low density lipoproteins
(VLDL) low density lipoproteins (LDL) high
density lipoproteins (HDL) Subfraction
intermediate density lipoproteins (IDL)
Electrophoretic mobility (charge) HDLs ?
?lipoproteins LDLs ?-?lipoproteins VLDLs
pre-? lipoproteins (intermediate between ? and ?
mobility).
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Lymph system Chylomicrons to capillaries via
lymph
INTEST INE
non-hepatic tissues
ApoB48 aids with chylo-micron assembly
LIVER
Figure 3. Exogenous pathway of lipid transport.
Chylomicrons carry dietary fatty acids to
tissues and the remnants take cholesterol to the
liver
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Triacylglycerol in core
Chylomicron (or VLDL)
To Liver
Apo CII
LIPOPROTEIN LIPASE
Glycerol
Free fatty acids
Polysaccharide Chain
Endothelial Surface of cell
Capillary
In cellulo (muscle adipose)
Free fatty acids
Figure 4. Lipoprotein lipase action on
chylomicron triacylglycerol (an identical
reaction occurs with VLDL)
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non-hepatic tissues
ApoB48
LIVER
Figure 3. Exogenous pathway of lipid transport.
Chylomicrons carry dietary fatty acids to tissues
and the remnants take cholesterol to the liver
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LPL hydrolyze TAGs FFA uptake LDL circulate to
tissues
non-hepatic tissues
LIVER
CII and E release to HDL
Cholesterol uptake excreted as bile acids
apo B100 on LDL bind to receptor
LDL taken into the cell to deliver cholesterol
Apo E binds liver receptor
HDL scavenge cholesterol
Figure 5. The liver-directed endogenous pathway
of lipoprotein metabolism.
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Chylomicrons Exogenous Pathway
Fig. 6 Chylomicron Processing and Interface with
HDL
HDL Both Pathways

• Nascent Chylomicron
• Assembly in Gut
• Mediated by B48

• Nascent HDL
• Assembled in liver
• Loans apo E/ apo CII to nascent chylomicrons

• Mature Chylomicron
• Apo E and CII added from HDL

• Mature Chylomicron
• Apo E and CII added from HDL
• CII activates LPL

• Lipoprotein Lipase
• capillary walls
• hydrolyzes TAG
• deliver FFA into adipose/muscle

• Mature HDL
• CE from peripheral cells via LCAT activated by
  apo A1
• Apo CII returned by chylomicrons

• Chylomicron Remnant
• from mature chylomicron
• apo CII returned to HDL

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sorting endosome ligand/receptor dissociation
transport vesicle- lysosome fuse forming late
endosome
Recycling of receptor
lysosome
Recycling of receptor and clathrin
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clathrin- coated pit
Golgi
late endosome
NPC-1 mediated transfer
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free pool of cholesterol
ACEH CE ? cholesterol B100 ? amino acids
ACAT (stimulated by cholesterol)
endocytosis
CE stored in droplets
vesicle
CE
CE
LDL CE
Cholesterol metabolism to bile acids or steroids
CERP
Membrane Cholesterol
L CA T
Reverse Cholesterol Transport
Figure 7. Cellular cholesterol uptake,
metabolism and release.
Mature HDL Cleared by liver