Lipid Transport Flashcards
Why is it difficult for lipids to be transported in the blood?
They are hydrophobic
So I soluble in water
How are lipids transported in the blood? (2)
Bound to albumin
As lipoprotein particles
What are the four components of phospholipids?
Polar hydrophobic head
Phosphate
Glycerol
Non polar fatty acid tail
How are phospholipids classified?
Give two examples
According to their polar head
Choline
Inositol
Where are the two sources of cholesterol?
Obtained from diet
Synthesised in the liver
What are three uses of cholesterol?
Modulates fluidity of membrane
Precursors of steroid hormones
Precursors of bile acids
How is cholesterol transported?
As cholesterol esters - linked to a fatty acid
What are the two types of proteins in a lipoprotein?
Peripheral apolipoproteins - on the outside
Integral apolipoproteins - pass through
What is the cargo of a lipoprotein made up of?
Triacylglycerol
Cholesterol ester
Fat soluble vitamins (ADEK)
What are the five classes of lipoproteins?
Chylomicrons
VLDL
IDL
LDL
HDL
How are lipoproteins classed?
How is this measurement obtained?
According to their density
Flotation ultracentrifugation
Compare the diameter of lipoproteins with their density
Describe an example
Inversely proportional
VLDL - lowest density but highest diameter
How many classes of apolipoproteins are there?
Name the two important ones
Six
ApoB apoAI
What are the two roles of apolipoproteins
Structural - package water insoluble lipid
Functional - ligands for cell surface receptors and cofactors for enzymes
Describe Chylomicron metabolism
- Produced in the small intestines
- ApoB48 added
- Enters lymphatic system
- Travels though thoracic duct into the left subclavian vein
- Acquires apoC and apoE
- ApoC binds to lipoprotein lipase on adipocytes and muscle
- Fatty acids are released from chylomicron into the cells
- When triglyceride levels are depleted to 20% apoC dissociates - leaving a chylomicron remnant
Describe what happens to the chylomicron remnants
- Return to the liver
- LDL receptors of hepatocytes bind to the apoE (on them)
- The remnant is taken up by receptor mediated endocytosis
Where are VLDL made?
What is their purpose?
Liver
Transport triacylglycerol
Describe VLDL metabolism
- ApoB added during formation
- ApoC and apoE added from HDL particles in blood
- VLDL bind to lipoprotein lipase on endothelial cells - in muscle and adipose
- VLDL starts to be depleted of triacylglycerol
What happens to the triacylglycerol in adipose and muscle cells during VLDL metabolism?
Muscle - fatty acids taken up and used for energy production
Adipose - used for resynthesis of triacylglycerol and stored as fat
What is derived from VLDL?
IDL and LDL
Describe the formation of IDL
- Triacylglycerol content of VLDL particle drops
- Some VLDL particles dissociate from the lipoprotein lipase enzyme complex and return to liver
- If it depletes to 30% it becomes an IDL
Describe the formation of LDL
- IDL particle rebinds to LPL enzyme
- Further depletion in triacylglycerol content
- Depletion to 10% - IDL loses apoC and apoE
What is the primary function of LDL?
How does this happen?
Provide cholesterol from liver to peripheral tissues
Peripheral cells have LDL receptors
Take up LDL via receptor mediated endocytosis
Why are LDL more susceptible to oxidative damage?
Do not have apoC or apoE - not efficiently cleared by liver
Half life in blood is longer