Lipid Digestion Flashcards
T or F: lipids are defined on the basis of chemical strucutre
False, they are defined on the basis of solubility properties
How many fatty acyl groups exist in a triglyceride and which position often holds unsaturated fatty acids?
- 3 fatty acyl groups
- 2nd carbon is typically linked to the unsaturated fatty acid
What makes biles salts both hydrophobic and hydrophile?
- The planar structure causes all of the -OH groups to be oriented on one side of the planar ring structure
- Carboxylate group extending off of the ring structure adds to the polarity of the structure as well
How can interference with bile reuptake cause a lowering of cholesterol?
- Cholesterol is a precursor to bile synthesis
- If bile is excreted rather than taken back up again then cholesterol will have to be used to make new bile
- This reduces the amount of free cholesterol as it is now fixed as bile
How much bile is lost and reuptaken in a normal person?
5% is lost
95% is taken back up
T or F: pancreatic lipase only works at a high pH?
True
What would happen if colipase production ceased in the pancreas?
- Lipase would not be able to perform as efficiently because colipase is needed to stabilize and localize lipase near the bile salt-TG particle
What reaction is performed by cholesterol esterase?
Cholesterol ester —> Cholesterol
- This is considered a lipase
What reaction is performed by phospholipase A2?
- Phospholipid gets an acyl group cleaved off of the two position on glycerol to create a Lysophospholipid
- This is considered a lipase
What two products of TG degreadation can be absorbed by the enterocyte?
- Fatty acids (aka diacylglycerols)
- 2-MG (monoacyl glycerol)
How much energy is needed to resynthesize TG from FA and Diacylglycerol (DAG)?
2 ATP are needed
What is the structure of a lipoprotein?
- Phospholipid form a mono layer making a micelle
- Cholesterol is interspersed in the phospholipids
- TG is located in the center of the sphere
- Apoprotein B (48 or 100) is located on the periphery of the sphere
- peripheral apoproteins are also present
How does the structure of a chylomicron differ from a lipoprotein?
In a lipoprotein the protein is nascent, this is not the case in a chylomicron.
What contributes to most of the mass in a chylomicron?
TGs
T or F: Apoprotein B-100 and B-48 come from the same gene.
True, the only difference is an early stop codon in Apo B-48.
What is the respective location of Apo B-100 and Apo-B48?
Apo B-100 = LIVER
Apo B-48 = INTESTINE
What are apoproteins used for?
- used to build a chylomicron around
What protein is needed to help assemble ApoB with lipids and TGs and where is it located?
- MTP (microsomal TG transfer protein)
- Located in the ER lumen
What is the sequence of movement triacylglycerides after they are reassembled from diacylglycerides and 2-MGs in the enterocyte cytosol up to the point of excretion?
- TAG enters the SER or RER
- MTP incorporates TG into the ApoB particle
- ApoB particle exits the ER and enters the golgi for further maturation
- Chylomicrons are then excreted from the gogli
Where is TG converted to 2-MG and FA for the first time?
In the intestinal lumen
How do TGs move in the blood?
They move as chylomicrons
When has a chylomicron reached full maturity?
when it has aquired ApoCII and ApoE
What are ApoCII and ApoE needed for?
ApoCII - needed for the chylomicron to interact with LPL (lipoprotein lipase)
ApoE - allows chylomicron remnant bind to receptors in the liver so that it can undergo reuptake as an endosome
What regulates the expression of LPL?
Insulin
