Lecture 9: Cholestrol Flashcards
Define cholestrol
important aspect of cell membranes, has a rigid ring system and a short branched hydrocarbon tail.
Cholesterol is largely hydrophobic.
But it has one polar group, a hydroxyl, making it amphipathic
How is cholestrol incoperated into cell membrane?
Cholesterol inserts into bilayer membranes with its hydroxyl group oriented toward the aqueous phase & its hydrophobic ring system adjacent to fatty acid chains of phospholipids.
The OH group of cholesterol forms hydrogen bonds with polar phospholipid head groups.
Two strategies by which phase changes of membrane lipids are avoided:
Cholesterol: In the absence of cholesterol, such membranes would crystallize at physiological temperatures.
The inner mitochondrial membrane lacks cholesterol but includes many phospholipids whose fatty acids have one or more double bonds, which lower the melting point to
below physiological temperature.
Defien triglyceride
are esters of long chain fatty acids and glycerol sometimes called triacylglycerol.
Define Lipoprotein
particles found in plasma that transport lipids including cholesterol
Lipoprotein classes
chylomicrons: take lipids from small
intestine through lymph cells
very low density lipoproteins (VLDL)
intermediate density lipoproteins (IDL)
low density lipoproteins (LDL)
high density lipoproteins (HDL)
Draw the structure of a plasma lipoprotein
Lecture Slide
Apolipoproteins purpose
major components of lipoproteins
responsible for recognition of particle by receptors
Lipoprotein brief description (shape, Apolipoproteins present and classification)
spherical particles with a hydrophobic core
apolipoproteins on the surface
Large: apoB (b-48 and B-100)
smaller: apoA-I, apoC-II, apoE
classified on the basis of density and electrophoretic mobility
Apoproteins of human lipoproteins
A-I (28,300)
- principal protein in HDL
- activate LCAT
A-II (8,700)
- occurs as dimer mainly in HDL
- enhance hepatic activity
B-48 (240,000)
– found only in chylomicron
B-100 (500,000)
– principal protein in LDL
- binds to LDL receptor
C-I (7,000)
– found in chylomicron, VLDL, HDL
-activate LCAT
C-II (8,800)
- found in chylomicron, VLDL, HDL
- activate lipoprotein lipase
C-III (8,800)
- found in chylomicron, VLDL, IDL, HDL
- inhibits lipoprotein lipase
D (32,500)
- found in HDL
E (34,100)
- found in chylomicron, VLDL, IDL HDL
- Binds to LDL receptor
H (50,000)
– found in chylomicron
Apolipoprotein versus lipoprotein
lipoprotein is an assembly of molecules whose function is to transport hydrophobic lipids in watery media including water and extracellular fluid whereas apolipoprotein is a protein bound to lipids in order to form lipoproteins.
Lipoproteins on gel electrophoresis
Lecture slide
Major lipoprotein classes: Chylomicron
formed through extrusion of resynthesized triglycerides from the mucosal cells into the intestinal lacteals
flow through the thoracic ducts into the suclavian veins
degraded to remnants by the action of lipoprotein lipase (LpL) which is located on capillary endothelial cell surface
remnants are taken up by liver parenchymal cells due to apoE-III and apoE-IV isoform recognition sites
VLDL Lipoprotein: Density Diameter: Type apolipoproteins present: Electrophoresis stage Formed?
density >1.006 diameter 30 - 80nm endogenous triglycerides apoB-100, apoE, apoC-II/C-III prebeta in electrophoresis
formed in the liver as nascent VLDL (contains only triglycerides, apoE and apoB)
nascent VLDLs then interact with HDL to generate mature VLDLs (with added cholesterol, apoC-II and apoC-III)
mature VLDLs are acted upon by LpL to generate VLDL remnants (IDL)
IDL are further degraded by hepatic triglyceride lipase (HTGL) to generate LDLs
IDL Lipoprotein Density Diameter: Type apolipoproteins present: Electrophoresis stage
density: 1.006 - 1.019
diameter: 25 - 35nm
cholesteryl esters and triglycerides
apoB-100, apoE, apoC-II/C-III
slow pre-beta
