L24: Lipid Metabolism V Flashcards
Explain the function and regulation of HSL.
- HSL=hormone sensitive lipase - In adipose tissue, HSL releases FFAs into blood by cleaving TAGs into glycerol and FAs - Inhibited by insulin
How do FFAs travel in blood? Why is this transport method important?
- They bind to hydrophobic pockets in albumin. - Don’t need to synthesize FFA transporters when we are in a starved state and need FFAs as albumin is always present.
Why is transportation of lipids problematic?
- FAs are mostly hydrophobic - TAGs are completely hydrophobic - Cholesterol is hydrophobic mostly
How are TAGs and cholesterol transported?
- They are transported inside of carriers known as lipoproteins – VLDL, IDL, LDL and HDL
What are chylomicrons? Where are they made? Are they made in liver?
- Made by enterocytes in intestine, these transport dietary lipids from site of absorption to adipose tissue. - Not made in liver
What are lipoproteins? What are the types? What are they composed of besides what they carry?
- Are carriers of triacylglycerol and cholesterol - VLDL, IDL, LDL and HDL - Composed of phospholipid/cholesterol coat that has apoproteins embedded in it
Types of apoproteins and functions?
- Apoprotein A: activates LCAT (lecithin:cholesterol acyltransferase), which generates cholesterol esters from cholesterols. Extracts lipids from membranes for reverse transport. - Apoprotein B: structural protein, interacts with lipoprotein receptors and mediates uptake of particle into target cells - Apoprotein C: modulate lipoprotein lipase (LPL) activity, which liberates FFAs and glycerol from lipoproteins - Apoprotein E: bind to receptors to allow removal of remnant particles from circulation
What is the function of apoprotein A?
- activates LCAT (lecithin:cholesterol acyltransferase), which generates cholesterol esters from cholesterols. Extracts lipids from membranes for reverse transport.
What is the function of apoprotein B?
- structural protein, interacts with lipoprotein receptors and mediates uptake of particle into target cells
What is the function of apoprotein C?
- modulate lipoprotein lipase (LPL) activity, which liberates FFAs and glycerol from lipoproteins
What is the function of apoprotein E?
- bind to receptors to allow removal of remnant particles from circulation
Describe role of chylomicron, where synthesized, association with apoproteins, source of apoproteins, destination of contents and formation / fate of chylomicron remnant.
What apoproteins do chylomicrons associate with? Where?
- Chylomicrons in enterocytes associate with ApoB-48 - After entering into serum, CM now associates with ApoC and ApoE, which is receives from HDL
Describe role of VLDL, IDL and LDL. Include where each are synthesized/formed, association with apoproteins, source of apoproteins, destination of contents and fate of lipoprotein.
What apoproteins do VLDL associate with? IDL? LDL? Where?
- VLDL associates with ApoB100 in hepatocytes - VLDL in serum associates with apoE and apoC obtained from HDL - IDL remains associated with all 3 per above - LDL remains associated with all 3 per above