Lipids and Lipoproteins
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These provide the transportation system for different types of water insoluble fatty substances
Lipoproteins
How are fats absorbed from diet and lipids synthesized by liver and adipose tissues, transported in the aqueous blood plasma?
associating non-polar lipids (triacylglycerol and cholesterol esters) with amhipathic lipids (phospholipids and cholesterol) and proteins to make water-miscible proteins
How do lipoproteins mediate the production of water-miscible lipoproteins?
They transport lipids from the intestine as chylomicrons and from the liver as very low density lipoproteins (VLDL) to most tissues for oxidation and to adipose tissue for storage.
What happens to excess calories in humans?
ingested in anabolic phase of feeding cycle followed by negative caloric balance when organism draws upon its carbohydrates and fat stores
How is lipid mobilized from adipose tissue?
as free fatty acid attached to serum albumin
What is the purpose of lipoproteins?
transport hydrophobic lipid (fat) molecules in water, as in blood or extracellular fluid
What specifically comprises lipoproteins?
single layer phospholipid and cholesterol outer shell *with non-polar core and single surface layer of amphipathic lipids
What consists the lipophilic or hydrophobic portions of each molecule?
Triacylglycerol and cholesteryl ester surrounded by a single surface layer of amphipathic phospholipids and cholesterol molecules
Lipoproteins may be separated according to what?
electrophoretic properties (alpha (-), beta (-) and pre beta (-) lipoproteins
T or F: the density of a lipoprotein decreases as the proportion of lipid to protein increases
true
types of lipoproteins
chylomicrons very high density lipoproteins low density lipoproteins HDL
lipoprotein which is the biggest and derived from intestinal absorption of triacylglycerol and other lipids
Chylomicrons primary concentration of fat that travel to different tissues
Chylomicrons are responsible for transport of what
dietary tryiglycerides (exogenous) from the GI tract to liver to skeletal muscle and to adipose tissue
Composition of chylomicrons
Phospholipids Cholesterol at core Triglycerides (90-95%) Protein (added by liver; if fats arent attached to proteins, lipoproteins should be increased like apolipoprotein B)
What happens after eating high fat food?
fat is emulsified by pancreatic lipase, increasing the surface area for absorption through the enterocyte. *intestinal lining contains receptors that absorb the esterified fat afte which, it goes to the blood then most of it goes to the liver
[Synthesis of chylomicrons] 1. -2. Where are lipid components assembled?
SER and golgi apparatus of mucosal cells with apoproteins (B-48 and A-apolipoprotein) synhesized in RER
[Synthesis of chylomicrons] 3. The assembled lipid components are called?
nascent chylomicrons *exocytosed into the lacteals of the intestinal villi; appear only after meals rich in fats
[Synthesis of chylomicrons] 4. How do nascent chylomicrons reach general circulation?
from lymph vessels (lacteals) via thoracic duct
[Synthesis of chylomicrons] 5. When are dietary lipids incorporated in chylomicrons?
following absorption in intestine
[Metabolism of chylomicrons] 1-2. What do the initial chylomicrons (synthesized by intestinal cells and only contain apoB-48 and apo A) acquire upon entering circulation?
apo C-II and apo E from plasma HDL to form mature chylomicrons
[Metabolism of chylomicrons] 3-4. T or F: apo E activates the enzyme lipoprotein lipase which causes hydrolysis of about 80-90% of the chylomicron triacylglycerols in the peripheral tissue such as muscles and adipose tissue
False, apo C-II
[Metabolism of chylomicrons] 5. What accompanies hydrolysis of chylomicron triacylglycerols?
transfer of most of the A and C-apolipoproteins to HDL. *changes convert chylomicrons into smaller particles (chylomicron remnants)
[Metabolism of chylomicrons] 7. What happens to the fatty acids and glycerol released from the hydrolyzed triacylglycerols
FA: enter muscle and adipose tissue cells Glycerol: enters the liver where it is used for synthesis of TAG
[Metabolism of chylomicrons] What happens to chylomicron remnants?
• removed from blood circulation by liver • bind to lipoprotein receptors on surface of hepatocytes • whole remnant particle is taken by hepatocyte via endocytosis