41 Blood Lipoproteins Flashcards
T/F, TGs, cholesterol and cholesterol esters (CEs) are too hydrophobic to travel in a free form in the blood?what are they packaged into?
T; lipoprotein
what is the lipoprotein made of?
They are packaged into the hydrophobic core of an aggregate of phospholipid, cholesterol and amphipathic proteins.
how are lipoproteins grouped?
according to density so less fat, greater protein content = higher density, more fat, less protein = lower density
what are chylomicrons?
carry dietary TGs from the intestine to peripheral tissues, especially muscle and adipose tissue
deliver cholesterol and phospholipids to the liver, found in the lymphatic fluid
what proteins are contained in the chylomicrons?
apoB-48 (nascent-new)- made in the intestinal epithelial, syn by rER
apo E and apo CII added from HDL in blood so that chylomicron becomes mature
if you see an apoprotein B-100, what type of lipoprotein is this? what is the apoprotein for chylomicrons?
VLDL; apoprotein B48
how are chylomicrons and VLDLs similar? what about LDL and HDL?
they carry TGs; LDL carries CE and HDL carries protein
what are the common dietary lipids?
triglycerides (TGs) and some phospholipids, cholesterol, cholesterol esters and fat soluble vitamins
what are the properties of dietary fat?
very hydrophobic and do not mix with the water medium. Very little digestion in saliva and stomach.
what facilitates the solubility of of lipid in the intestines?
is facilitated by bile salts (BS) and “detergent” molecules: amphipathic molecules that emulsify dietary TGs and other lipids into micelles (microdroplets or chylomicrons).
where are bile salts made? stored?
liver; gallbladder
what are detergent molecules formed from?
TGs and PLs
T/F, If bile salts and detergent molecules aren’t present, fats will clump together to minimize water contact, form large droplets, clog the digestive tract and be eliminated fairly intact (steatorrhea).
T
how are soluble are small and medium chain fatty acids? (8-10C)
soluble enough to be absorbed directly and can move into the portal vein without bile salt involvement.
what are the functions of bile salts?
enter digestive tract and assist lipid digestion and absorption, acting as a “detergent” that breaks up fat droplets
describe the polar properties of bile salts?
Polar and non-polar properties that allow molecule to dissolve a variety of compounds
where are bile salts recycled back to?
the liver
what is pancreatic lipase?
A water soluble enzyme that removes fatty acids from TGs
what is the cofactor of pancreatic lipase? how does it work with pancreatic lipase?
co lipase; they both bind to emulsified TGs at the lipid water interface
dietary phospholipids are hydrolyzed by this phospholipase to form these two products?
pancreatic phospholipase A2 to form lysophospholipid and a free fatty acid.
what is Lysophospholipid?
powerful detergent that aids in the emulsifying action of bile salts
what cholesterol ester?
fat is added onto the oxygen and this happens when we eat fat in our diet. It is more common and more hydrophobic plus easier to store in tissues and so these two have to processed separately by a cholesterol esterase
how does fat uptake and resynthesis of TG in Epithelial Cells work?
Once in side the enterocyte:
Two free FAs and one 2-monoacylglycerol recombine into TG
enzymatic process on smooth ER
FAs are first activated by acetyl CoA, add sequentially to form TG (more in later lecture)
Reformed TGs are packaged into chylomicrons for transport
what do chylomicrons contain?
TGs which are contained within shell (largest component)
Cholesterol which partitions with the phospholipids
Cholesterol esters, which partitions within the shell
Fat soluble vitamins that partition within the hydrophobic core
Proteins on the surface of the particle: dictate function / recognition
is the gene for apoB protein the same in liver and intestines? what are the differences?
yes; apoB-48 is the major apoprotein associated with chylomicrons
apoB-48 is a smaller version of the apoprotein B-100, which is synthesized in the liver and is the major protein of VLDL
why is microsomal triglyceride transfer protein (MTP) important to chylomicrons and VLDL?
target for fat management
microsomal triglyceride transfer protein (MTP) transfers lipid and TG across ER membrane and into the ApoB particle as it is made in the ER lumen.
MTP binds to B-lipoproteins (chylomicron and VLDL) and is activated.
what is happens without Blood lipoproteins in the blood for abetalipoproteinemia? what is missing that causes this condition?
fat goes into intestines and is eliminated with feces; MTP is missing so chylomicrons and VLDLs aren’t formed.
what do VLDLs carry? size compared to chylomicrons? what is the main difference?
endogenously synthesized TGs, cholesterol and cholesterol esters from the liver to tissues, especially TGs to muscle and adipose tissue; Smaller than chylomicrons, slightly higher density
Major difference is the presence of apo B100 rather than apo B48
what are LDLs?
they are rich in cholesterol and cholesterol esters; Delivers cholesterol and cholesterol esters to all peripheral tissues
Primary cholesterol transport mechanism.
what are the receptors of the blood lipoproteins? what does it recognize?
LDL receptor; recognizes apoE and apoB100 and Binds LDL, VLDL, IDL and chylomicron remnants
Its job is to bind lipoproteins and bring them into the cell by endocytosis
For LDLs, that means delivering cholesterol and cholesterol esters
what are HDLs?
HDLs pick up cholesterol from tissues:
esterify it by LCAT and transport cholesterol esters to IDL transforming IDL to LDL
OR…carry CEs back to the liver
pick up apolipoproteins released from other lipoproteins or act as a reservoir to donate apoproteins to other lipoproteins
whats the size of an HDL? protein/density content?
Smallest blood lipoprotein with the highest protein content, thus the highest density
Nascent HDL are synthesized released from the liver and intestinal cells
what is HDL esterified by?
LCAT (lecithin-cholesterol acyl transferase)
Cholesterol esters are transferred to IDL or transported back to the liver
HDLs pick up apoC-I,II and III and apoE as they are released from VLDL and chylomicrons
