Lipoproteins

Front 1

Role of lipoprotein in the circulation.

Back 1

• Transport both Tags & cholesterol.
• Posses a hydrophobic core (Tags & cholesteryl esters) and an amphipathic outer layer

Front 2

Composition, function, location of synthesis and delivery of HDL.

Back 2

•synthesized; liver and small intestines

•Composition; rich in A-I, C-I, C-II and E and small amounts of cholesterol & cholesterol esters
high in protein

•Function; transport cholesterol (esters) back to the liver = reverse cholesterol transport

Front 3

Composition, function, location of synthesis and delivery of LDL.

Back 3

•Synthesized; liver from VLDL via IDL

•Composition; ApoB100, High in Cholestrol (50%)


•Function; bad = circulate & take cholesterol to peripheral, found in athersclerosis plaque

Front 4

Composition, function, location of synthesis and delivery of VLDL.

Back 4

•Synthesized; Made in smooth ER

•Composition; B100, as well as small amounts of C-I, II, III and E on outer

•Function; transport endogenous lipids

Front 5

Composition, function, location of synthesis and delivery of Chylomicron.

Back 5

•Synthesized; intestinal cells and secreted into lymph

•Composition; B48, A-I, A-II, and A-IV

•Function; Exogenous pathway

Front 6

Describe the reaction involving lipoprotein lipase.

Back 6

•extracellular enzyme on adipose and skeletal

•dual functions of triglyceride hydrolase and ligand/bridging factor for receptor-mediated lipoprotein uptake.
- VLDL is converted to IDL and then to LDL.
- cholesterol converted to remnants

Front 7

Describe the reaction involving LCAT.

Back 7

Helps converts HDL → HDL2 → HDL3
reverse cholesterol transport

Front 8

Describe the reaction involving ACAT.

Back 8

Esterfies excess intracellular cholesterol to more hydrophobic fatty acids for storage

Front 9

Describe the role of CETP.

Back 9

• Central role in HDL metabolism
o Cholesterol ester (lipids) from HDLs → VLDL & LDLs
o Tags from VLDL → LDLs & IDLs

Front 10

Exogenous Pathway.

Back 10

1. Transport dietary lipids around the body
2. In intestine, Tags are broken down by water-soluble pancreatic lipase (requires colipase & bile salt)
3. Tags are hydrolyzed to 2 free fatty acids and a monoglyceride that are absorbed (carrier-mediated) and reformed to Tags in the enterocytes
4. Inside the enterocytes, Tags are incorporated into chylomicrons for transport around the body
5. In the lymphatics, growing chylomicrons pick up C-II and E from HDLs
6. reduced by lipase leaving behind a chylomicron remnant
7. Remnant donates A and C back to HDL but retains B48 and E
8. Relived from blocking effects of C, E now recognizes remnant receptors on hepatocytes
9. Now is engulfed, disassembled and repackaged to VLDL in the liver

Front 11

Endogenous Pathway.

Back 11

• Endogenous lipids transported by VLDL
• Made in smoother ER of hepatocytes (muscle & adipose)
• Tags are oxidized for energy or stored
• VLDL processed in the golgi & secreted from the liver contains tags, cholesterol, cholesteryl esters and B100, as well as small amounts of C-I, II, III and E on outer shell

1. VLDL circulate in the capillaries of peripheral tissues, E and C-II increase as they’re donated by HDLs
2. Hydrolysis of Tags by lipase proceed, VLDL become rich in cholesteryl esters = IDL
3. IDL donate C and E (retains B100) to HDL and shrink
4. Now further enriched in esters = LDL
5. Both IDL and LDL may bind to LDL receptors on hepatocytes and extraheptic tissue, and are taken up by receptor-mediated endocytosis

Front 12

Describe a person's lipoprotein profile after eating.

Back 12

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Front 13

Describe apolipoprotein A.

Back 13

• A-I; pick up cholesterol from cell membranes
• Essential for HDL assembly and is a cofactor of LCAT
• Low plasma levels = increase risk for CAD

Front 14

Describe apolipoprotein B100.

Back 14

o synthesized in the liver and is incorporated in VLDLs
o As IDL & LDL are formed from VLDLs, they also contain B100
o Interacts with specific LDL recpetors on hepatocytes
o 95% of LDL is B100
o elevated plasma levels = atherosclerosis

Front 15

Describe apolipoprotein B48.

Back 15

o Synthesized in intestinal epithelium
o Found exlusively in chylomicrons
o Chylomicrons cannot be secreted from intestine without B48
o Required for chylomicrons assembly

Front 16

Describe apolipoprotein C1.

Back 16

• C-I may be activated by LCAT

Front 17

Describe apolipoprotein C2.

Back 17

• C-II is the best characterized, produced in the liver and activating cofactor of lipoprotein lipase (may only degrade tags in particles that possess C-II)

Front 18

Describe apolipoprotein C3.

Back 18

• C-III inhibitor of lipase

Front 19

Describe apolipoprotein E

Back 19

• E I, E II, E III
• Found primarily on tag-rich lipoproteins, chylomicrons remnants, IDLs, VLDLs and HDLs
• Able to interact with specific hepatic receptors (different isoforms bind different affinity)
• When present on IDLs, E enhances the interaction of B100 with hepatic LDL receptors