Lipid Transport Flashcards
Smallest methods of lipid transport is?
Bound to Albumin by non-covalent bonds
On 2% of lipids transported, mostly FA. -3mmol/L
Albumin produced in liver, high levels indicate high protein diet or dehydration, low indicates kidney-liver damage
Why is it hard to transport lipids on their own?
Lipids are hyrodphobic hence must be carried
Largest method of lipid transport?
Lipoproteins particles in the plasma.
Transports 98% of lipids.
What are Micelles?
Polar molecules of proteins and phospholipids with cholesterol for stability.
They are APOLIPOPROTEIN composition
What do lipoproteins transport?
Triacylglycerides Cholesterol esters (transport form)
How big are the lipoproteins?
5-100 nm
How do lipoproteins vary?
Density
Surface
Function
Describe the different classes of lipoproteins?
Each class has own lipoproteins A-H Determined by enzyme activation from recognition on cell surface receptors or POLYMORPHISM esp ApoE because different phenotype so exist hence different expression.
Characteristics of APOLIPOPROTEIN?
Packages non-water soluble lipids in a hydrophilic case.
Contains hydrophobic and hydrophilic
What Chylomicrons?
The least dense Apoproteins + TAGs to transport lipids. Released from intestine endothelium of blood vessels, transported via lymphatic system to cells.
This gives the lymphatic vessels a white appearance after a fatty diet.
What are Very low density lipoproteins?
VLDLs
2nd least dense lipoproteins.
Formed by liver to store energy.
TAGS+ specific apoproteins to carry lipids from liver to tissue
What are LDLs?
Low density lipoproteins?
Cholesterol rich and contains specific Apoprotiens (Apo B100)
Formed in liver
2nd MOST dense
The more LDLs, the higher the risk of atherscelorisis
What are HDLs?
The most dense lipoproteins.
Formed by tissue.
Carries excess cholesterol from tissue and arteries to liver where disposed at bile salts.
HDL>LDL is good!
What are NASCENT HDLs?
Some HDLs synthesised as shells by liver/from vLDL remnants.
They pick up cholesterol from capillaries then mature into HDLs and take back to liver
What are the characteristics of lipoproteins?
Their surface coat is comprised of phospholipids, cholesterol and apoproteins
Sphere shape provides stability
The ratio of core to surface lipids ensures stability. Removal of core lipids meNd the surface must shrink.
Can only remove the core lipids using enzymes, eg lipase, transferase proteins.
Explain how the tissue obtain the lipids they require FOR the lipoproteins?
Lipase on plasma membrane of endothelium of capillaries.
Chylomicron bonds to vLDLs.
Cleaves TAGs into Glycerol and FA by hydrolysis.
Gylerol is in circulation.
FA goes into tissues for metabolism
vLDL remnants (chylomicrons) removed by liver and converted into other lipoproteins
What is Receptor-mediated Enocytosis?
Cholesterol transfer using LDLs
- cells have LDL receptors.
LDL containing cholesterol esters binds to the ApoB-100 receptors causing the cell to wrap around the lipoprotein
The complex then separates into a membrane of receptors which returns back on to the plasma membrane, and a sphere of the lipoprotein.
Lysosomes digests the cholesterol esters to release the FA & free cholesterol
How is LDL receptor expression regulated?
By cholesterol uptake.
If cholesterol is taken up, synthesis is inhibited in cell.
Hence less LDL receptors leads to excess cholesterol.
Biosynthsis vs uptake: cholesterol?
Cells can biosynthesise cholesterol from Acetyl-CoA, but prefer uptake of PRE-FOREMD cholesterol from blood
What is HYPERLIPOPROTEINAEMIAS?
Raised levels of 1 or more classes of lipoproteins
Due to over-production or under-removal.
Why might there be a defect?
Enzymes
Receptors
Apoproteins
What diseases is Hyperlipoproteinaemias linked to?
Atherosclerosis and Coronary Artery Disease.
This occurs with high LDLs and cholesterol in blood.
What diseases can Hyperlipoproteineamias cause?
Xanthelasma
&
Corneal Arcus
What is Xanthelasma?
Cholesterol deposits in skin.
Can also occur in tendons and joints.
