25. Lipids and Lipoproteins Flashcards
TAGs (triacylglycerides) contain almost 7 times as much energy as do? about 100,000kCal in TAGs in fat/muscle
carbohydrates/glucose
The major source for TAG synthesis in intestinal cells are?
Dietary triacylglycerides
Dietary TAGs are broken down into FA and MAGs in the intestinal lumen, and then intestinal cells remake TAGs using the MAG back bone. What is the product after TAGs synthesis in the intestinal cells?
Chylomicron which is TAGs with apolipoproteins (APO) and other lipids which are released in the lymphatic system and enter the blood via the thoracic duct
The major source for TAG synthesis in the liver/hepatocytes are?
** Glucose(carbohydrates) **
Acetyl CoA and Glycerol
What is different in TAG synthesis in the liver regarding glycerol compared to other processed in the intestine and adipocytes?
Glycerol is able to be made into Glycerol3P by glycerol kinase unique to liver TAG syn
Intestinal cells use MAG as a backbone, Hepatocytes use G3P as a backbone for TAG synthesis and what do adipocytes use?
G3P as well!
In the liver, what is the final product of TAG synthesis?
Very Low Density lipoproteins (VLDL), released into blood
For storage of TAGs in adipocytes, glucose via insulin activated GLUT4 transporter is used along with what other two sources?
The chylomicron from intestines and VLDL from the liver
How are chylomicrons and VLDL broken down to form FAs in adipocytes?
Via capillary lipoprotein lipase***
DAGs and some TAGs are broken down via HORMONE sensitive lipase (HSL) which is activated by glucagon, E/NE and inhibited by insulin (fed state). How are DAGs and MAGs are broken down?
LPL lipoprotein lipase for DAGs
MAGs via monoacylglycerol lipase
How are short chain FA transported compared to longchain fatty acids?
Short are able to travel within the blood freely
Long bind to albumin (carrier protein) for trasnport
HSL is modulated by hunger and exercise. Glucagon, epinephrine and norepinephrine will _______ HSL making it active to promote lipolysis in adipocytes while insulin will do what?
Phosphorylate HSL to become active
Insulin dephosphorylates to inactivate and stop lipolysis
What is the main lipase to breakdown TAGs after further experiments?
ATGL adipose triglyceride lipase
During hunger and exercise, Glucagon/epinerphrin bind to GPCR which activates AC and PKA which will phospharylate perilipin to its active form, which makes HSL into its active form by phosphorylation to break down DAGs. What is perilipin?
A protein that coats lipid droplets in adipocytes, preventing activation. Overexpression inhibits lipolysis and without perilipin, there would be lots of fat break down
What is the main substrate that forms cholesterol?
acetyl CoA
Lipoproteins are vehicles for transport of cholesterol, TAGS and other things. They contribute to lipid metabolism by doing what two things?
- Serve as ligands that bind to receptors to internalize lipoproteins
- Activate Enzymes
What are the 5 different types of lipoproteins?
chylomicron from intestine VLDL from liver IDL LDL HDL
HDL contains mainly proteins and little fats and cholesterol, this is why it is considered a good fat. What is the main contributor to Chylomicrons, VLDL and IDLs and what is the main contributor to LDLs?
Chylomicrons, VLDL, and IDLs are most TAGs
LDLs are more than 50% cholesterol, this is why they are considered bad fats
Chylomicrons are formed from dietary fats, is the largest lipoprotein, least dense and has high TAG content. What are the 3 apolipoproteins on the outer shell?
unique to it ApoB48 which facilitates transport
ApoCII which activates capillary lipoprotein lipase to store in adipocytes!
ApoE facilitates uptake into liver
VLDL from liver have the same ApoCII to activate capillary lipoprotein lipase and ApoE for uptake into liver, what is the different B protein that it has?
ApoB100: binds to LDL and makes sure it is taken up and not allowed in blood (increase cholesterol)
IDL have both ApoB100 and ApoE while LDL only have?
ApoB100
HDL are the smallest and most dense and consist mainly of proteins. It has ApoCII and ApoE like the others but has ApoAI which does what?
activates an enzyme to convert cholesterol into cholesterol ester
The chylomicron is formed in the intestines and ApoCII and ApoE are added by HDL. capillary lipoprotein lipase cleaves apocII leaving it withApoE and ApoB48 which then does what?
binds to ApoE receptor in liver
VLDL are assembled in the liver and have all 3 Apo. Capillary lipoprotein lipase cleaves ApoCII and gives back to HDL, leaving you with IDL. IDL via hepatic lipoprotein lipase cleaves ApoE, leaving you with LDL. What does LDL do?
Bind to LDL receptor on target cell for uptake. If the receptors are defective, resulting in LDL in the bloodstream, can lead to atherosclerosis
