LECTURE 16 - TRIACYLGLYCEROLS Flashcards
how are free fatty acids transported in an aqueous environment?
partly soluble in water, form micelles
how are triacylglycerols transported in an aq environment?
transported by lipoproteins in plasma or lipid droplets in cells
how are phospholipids transported in an aq environment?
form a bilayer and make vesicles
how are triacylglycerols from the diet transported in the blood and the type of metabolism?
transported by chylomicrons, which are lipoproteins produced right after a meal
exogenous metabolism: comes from the diet
how are endogenous triacylglycerols transported in the blood?
the liver can do this without food
produces VLDLs
where does lipolysis happen?
happens in lipid storage droplets?
what is the triglyceride journey in endogenous metabolism?
- synthesized
- transported by VLDLs
- stored
- mobilized to generate energy
what is the triglyceride journey in exogenous metabolism?
- ingested
- transported by chylomicrons
- stored
- mobilized to generate energy
when does the pancreatic lipase reaction happen?
during + after a meal, in the fed state
where does the pancreatic lipase reaction happen?
in the GI tract
what is the pancreatic lipase reaction and what regulates it?
pancreatic lipase breaks down triglycerides into monoglyceride+free fatty acids
regulated by substrate availability
how can charged free fatty acids go through the non polar membrane bilayer?
can either diffuse or go through a transporter
OR
mechanism of pinocytosis:
1. in the extracellular fluid, the pH is 7 and the fatty acid is still charged
2. when it is internalized in a vesicle, the pH is lower and the FA is protonated, it becomes neutral
3. as it is neutral, it can cross the bilayer of the vesicle to go in the cytoplasm
4. when it enters the pH 7 of the cytoplasm it becomes charged again
where does the lipoprotein lipase reaction (LPL) happen?
surface of muscle and adipose cells
when does the lipoprotein lipase reaction (LPL) happen?
happens during + after a meal, in the fed state
what is the LPL reaction?
triglycerides are cut into monoglyceride + free fatty acids by LPL
how is the LPL reaction regulated?
by substrate availability
what is composition of adipocytes?
store large amounts of triglycerides as fat droplets that nearly fill the cell
the nucleus is pushed to the side
what do lipid droplets in the liver look like?
much smaller than in adipocytes
serve as transient buffer reservoir of esterified FAs and esterified cholesterol
these types of lipid droplets can also be found in small quantities in the muscle cells
when does lipolysis in lipid droplets happen?
during fasting or exercise
what is the process of lipolysis in lipid droplets?
3 enzymatic reactions
triacylglycerol-> diacylglycerol by ATGL
diacylglycerol -> monoacylglycerol by HSL
monoacylglycerol -> glycerol by MGL
the free fatty acids that are chopped off travel to the blood with albumin and glycerol does not need a carrier
how is lipolysis regulated by hormones?
very tight regulation
1. hormone binds to GCPR which activates G alpha S
2. this activates adenylate cyclase, which will make cAMP from ATP
3. cAMP will activate PKA
4. PKA will phosphorylate and activate hormone sensitive lipase (HSL) as well as perilipin
5. perilipin is a coating protein around lipid vesicle
6. when phosphorylated, perilipin changes conformation and allows HSL inside the vesicle
7. the fatty acids travel to the blood and then to wherever they need to go
how does triglyceride synthesis in enterocytes happen?
stored in the double membrane of the ER
the ER membrane bulges out and then the the neutral triglycerides can be inside this single layer lipoprotein
the first step:
activation by CoA via acyl-CoA-synthetase
the hydrolysis of PPi drives this reaction forward
the second step:
2-monoacylglycerol (from diet) is made into diacylglycerol by MGAT and reacts with acyl-CoA
diacylglycerol is made into triacylglycerol by DGAT, by reaction with Acyl CoA
how are triacylglycerols synthesized de novo in the liver and adipose tissue?
step 1: generate of G3P from DHAP or the phosphorylation of glycerol (not in adipocytes bc they dont have glycerol kinase)
step 2: acyl CoAs are added from Acyl CoA synthetase
step 3: at this point you can make phospholipids or you can continue with the enzyme lipin, which is the key regulatory enzyme, makes DAG
step 4: adding more Acyl CoA
how does insulin stimulate lipogenesis?
stimulates lipogenesis via transcriptional control
