LECTURE 16 - TRIACYLGLYCEROLS

Question 1

how are free fatty acids transported in an aqueous environment?

Answer 1

partly soluble in water, form micelles

Question 2

how are triacylglycerols transported in an aq environment?

Answer 2

transported by lipoproteins in plasma or lipid droplets in cells

Question 3

how are phospholipids transported in an aq environment?

Answer 3

form a bilayer and make vesicles

Question 4

how are triacylglycerols from the diet transported in the blood and the type of metabolism?

Answer 4

transported by chylomicrons, which are lipoproteins produced right after a meal
exogenous metabolism: comes from the diet

Question 5

how are endogenous triacylglycerols transported in the blood?

Answer 5

the liver can do this without food
produces VLDLs

Question 6

where does lipolysis happen?

Answer 6

happens in lipid storage droplets?

Question 7

what is the triglyceride journey in endogenous metabolism?

Answer 7

1. synthesized
2. transported by VLDLs
3. stored
4. mobilized to generate energy

Question 8

what is the triglyceride journey in exogenous metabolism?

Answer 8

1. ingested
2. transported by chylomicrons
3. stored
4. mobilized to generate energy

Question 9

when does the pancreatic lipase reaction happen?

Answer 9

during + after a meal, in the fed state

Question 10

where does the pancreatic lipase reaction happen?

Answer 10

in the GI tract

Question 11

what is the pancreatic lipase reaction and what regulates it?

Answer 11

pancreatic lipase breaks down triglycerides into monoglyceride+free fatty acids
regulated by substrate availability

Question 12

how can charged free fatty acids go through the non polar membrane bilayer?

Answer 12

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

Question 13

where does the lipoprotein lipase reaction (LPL) happen?

Answer 13

surface of muscle and adipose cells

Question 14

when does the lipoprotein lipase reaction (LPL) happen?

Answer 14

happens during + after a meal, in the fed state

Question 15

what is the LPL reaction?

Answer 15

triglycerides are cut into monoglyceride + free fatty acids by LPL

Question 16

how is the LPL reaction regulated?

Answer 16

by substrate availability

Question 17

what is composition of adipocytes?

Answer 17

store large amounts of triglycerides as fat droplets that nearly fill the cell
the nucleus is pushed to the side

Question 18

what do lipid droplets in the liver look like?

Answer 18

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

Question 19

when does lipolysis in lipid droplets happen?

Answer 19

during fasting or exercise

Question 20

what is the process of lipolysis in lipid droplets?

Answer 20

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

Question 21

how is lipolysis regulated by hormones?

Answer 21

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

Question 22

how does triglyceride synthesis in enterocytes happen?

Answer 22

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

Question 23

how are triacylglycerols synthesized de novo in the liver and adipose tissue?

Answer 23

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

Question 24

how does insulin stimulate lipogenesis?

Answer 24

stimulates lipogenesis via transcriptional control