Lipid Synthesis and Transport Flashcards
How is TAG used in the body (general)?
TAG in small intestine transferred into blood.
Liver TAG transfered into blood.
Moves into muscle to be oxidised to generate ATP.
Moves into adipose tissue to be stored.
Where does fatty acid synthesis occur?
In the cytosol of liver cells
What hormone stimulates fatty acid synthesis?
Insulin
What is the starting molecule in fatty acid synthesis?
Acetyl CoA
How is acetyl CoA transported from mitochondrial matrix into the cytosol?
In mitochondria: Acetyl CoA + oxaloacetate > citrate
Citrate passes through mitochondrial membrane.
In cytosol: citrate > acetyl CoA + oxaloacetate
Outline step 1 of fatty acid syntheis. Reaction, enzyme etc.
Acetyl CoA + HCO3- > Malonyl CoA
Enzyme: acetyl CoA carboxylase
Uses ATP > ADP + Pi
How is acetyl CoA carboxylase activated, what does it do?
Activated by insulin.
Coverts Acetyl CoA into Malonyl CoA.
How does malonyl CoA signify the fed state?
Malonyl CoA inhibits carnitine transferase
- prevents transferral of fatty acids into the mitchondria to be oxidised.
- stops fatty acid breakdown.
Outline steps 2 and 3 in fatty acid synthesis.
Step 2: Malonyl reacts with another acetyl CoA and loses a carbon. (Adds 2 and loses 1).
Step 3: Subsequent addition of a malonyl CoA and removal of one carbon. (Adds 3, loses 1)
CATALYSES BY FATTY ACID SYNTHETASE.
What co-factor is needed for fatty acid synthesis?
NADPH - acts as a reducing agent.
Provided by hexose monophosphate shunt.
How are triacylglycerides synthesised in liver cell?
Glycerol is activated by phosphorylation to glycerol phosphate.
Glycerol phosphate + 3fatty acids > Triacyl glyceride + phosphate
What is a lipoprotein?
Protein-lipid complex used to transport TAG in blood.
What are the 4 main types of lipoprotein and what do they carry?
Chylomicrons (carry mainly TAG - biggest + lowest density)
Very-low density lipoprotein (VLDL) - Endogenous TAG, Produced in the liver.
Low-density lipoprotein (LDL) - mainly carries cholesterol
High density lipoprotein (HDL) - takes cholesterol to liver
What is the general structure of lipoproteins?
Inner core = triacyl glycerol + choesterol esters
Outer surface = single layer of phsopholipid, cholesterol and apoproteins.
What are the 3 roles of apoproteins? Give examples.
- Some required as structural components:
- Apo B-48 in chylomicrons
- Apo B-100 in VLDL - Some activate enzymes:
- apo C-II on chylomicrons activates lipoprotein lipase (removes fatty acids from TAG) - Some as destination targetting signals - bind to specific receptors on cel surface to allow uptake of lipoprotein into cell.
- apo B-100 on LDL binds to LDL receptors
- apo E on chylomicrons bind to liver remnant receptors.
How is exogenous fat (from intestinal lumen) transported?
- Chylomicron bound to apo-48 enters circulation.
- Picks up apo E and apo C-II.
- TAG in chylomicron broken down by lipoprotein lipase to fatty acids and glycerol. Fatty acids enter adipocyte where they are stored.
- Chylomicron remnant is still bound to apo E and apo B-48.
- Apo E binds to receptor on liver surface casing uptake of the chylomicron remnant into the liver.
What apoprotein activates lipoprotein lipase?
Apo C-II
What apoprotein stabilises chylomicrons?
Apo B-48
What apoprotein allows uptake of chylomicron remnant into liver cells?
Apo E binds to apo E receptors on liver cell surface.
What sort of lipoprotein transports exogenous fat?
Chylomicrons
What sort of lipoprotein transports endogenous fat?
VLDL/LDL
How is endogenous fat transported around the body?
- Starts in liver as VLDL bound to apo B-100 - trnasported out of liver into blood.
- apo E and apo C-II is transferred from HDL onto the VLDL.
- Apo C-II activates lipoprotein lipase - stores fat in adipocyte.
- VLDL becomes LDL as TAG is removed into adipocyte.
- apo C-II and apo E are returned to HDL.
- LDL associated with B-100. B-100 receptors on peripheral tissue and liver. 50/50 uptake.
What is the function of HDL?
Transports cholesterol out of cells.
What enzyme esterifies cholesterol to form cholesterol esters?
LCAT enzyme - converts phosphatidy choline to lipophosphatidy simualtaneously.
