Lipid transport Flashcards
what are the 5 lipoprotein transporters
chylomicrons VLDL IDL LDL HDL
true or false: lipids are hydrophilic
false - they’re hydrophobic which makes them difficult to transport in the blood
how are fatty acids transported in the blood
by being carried by albumin
how are 98% of lipids transported
in lipoprotein particles
describe phospholipid molecules
- they have a hydrophobic tail made up of 2 fatty acids
- glycerol backbone
- phosphate
- polar hydrophilic head attached to the phosphate
what part of the phospholipid classifies it
the hydrophilic head which can be either choline or inositol
what shape of phospholipids carry aqueous cargo
liposome
what shape of phospholipids carry hydrophobic cargo
micelle
where is most of the bodys cholesterol obtained
from synthesis in the liver
small amount comes from the diet
what is cholesterol used for
- for stability in membranes
- precursor to steroid hormones
- precursor to bile acids
give 4 examples of steroid hormones
oestrogen
testosterone
aldosterone
cortisol
how is cholesterol transported around the body
it is converted into cholesterol esters but LCAT enzymes
what are apolipoproteins
proteins found either passing through the phospholipid membrane (peripheral) or on the surface (integral) of lipoproteins
what are the functions of apolipoproteins
- allows lipoprotein molecule to form by allowing packaging of the water insoluble contents
- act as cofactors for enzymes to break down lipids
- act as ligands to receptors to take up cargo
what does the density of lipoproteins depend on
the amount of apolipoproteins on their surface
in a flotation ultracentrifugation which lipoprotein migrates the furthest
HDL
for more dense lipoproteins what happens to the size of their diameter
It decreases
what apolipoprotein is added to chylomicrons before they enter the lymphatic system
apoB-48
when chylomicrons enter the left subclavian vein what other apoproteins are added
apoC and apoE
what does the addition of apoC to chylomicrons allow
the binding to lipoprotein lipase on adipocytes and muscle allowing the chylomicrons to release their fat
what do chylomicrons mostly contain
dietary fat
what do VLDL contain
TAGs synthesised by the liver
what happens to chylomicrons when the TAG content is reduced to 20%
the apoC dissociates and the chylomicron becomes a chylomicron remnant
what happens to chylomicron remnants
they return to the liver and the apoE allows it to bind to LDL receptors on hepatocytes to be taken up by receptor mediated endocytosis
where is VLDL synthesised
in the liver
what apoproteins bind to VLDL
apoB100, apoC and apoE
how do VLDL become depleted
they bind to LPL in the muscle and adipose cells
what happens to the fatty acids taken up by muscle and adipose cells
muscle - used in energy production
adipose - resynthesised to TAGs and stored
how are IDLs formed
when the TAG content of VLDL drops to 30%
how are LDL formed
when the TAG content of IDL depletes to 10% and so loses its apoC and apoE
what happens to IDL particles
- can be taken up by the liver
- or can rebind to LPL to be further depleted
what is the cholesterol content in LDLs like
very high
what is the function of LDL
provide cholesterol from thee liver to tissues
how are LDLs taken up by cells
attach to LDL receptor then taken up by receptor mediated endocytosis
why aren’t LDLs efficiently cleared up by the liver
as Liver LDL receptors have a high affinity for apoE which the LDL doesn’t have
why do LDLs become oxidisied
they have a long half life so are more susceptible to oxidative damage by free radicals
outline receptor mediated endocytosis for LDLs
- LDLs have the apoB100 as a ligand which binds to LDL receptors on cells requiring cholesterol
- complex is taken up by endocytosis
- fuse with lysosomes for digestion as release of cholesterol and fatty acids
how are nascent HDLs synthesised
- by the liver and intestine in low TAG levels
- bud off from chylomicrons and VLDL as they’re digested by LPL
- from apoA1 can aquire cholesterol and phospholipids to form the HDL
how are the nascent HDLs filled
- they can accumulate phospholipids and cholesterol from cells lining blood vessels
- core progressively fills
- this doesn’t require enzymes
what do HDLs do
remove cholesterol from cells and returns it to the liver
what do HDLs reduce the likelihood of
foam cell and atherosclerotic plaque formation
what protein facilitates the transfer of cholesterol to HDLs
ABCA1
what happens to the cholesterol when it enters HDLs
it is converted into cholesterol esters by LCAT
as well as the liver where else might HDLs deliver cholesterol to
steriodogenic cells as they have a scavenger receptor to allow this
what protein allows the exchange of cholesterol ester for TAG between HDLs and VLDLs
cholesterol exchange transfer protein
what is hyperlipoproteinaemia
where there is raised plasma levels of one or more lipoproteins classes
what causes hyperlipoproteinaemia
- over production
- under removal
what causes type I, IIa and III of hyperlipoproteinaemia
I - defective lipoprotein lipase
IIa - defective LDL receptor
III - defective apoE
what are the clinical signs of hypercholesterolaemia
- xanthelasma - yellow patches on eyelids
- tendon xanthoma - nodules on tendons
- corneal arcus - white circle around eye
what does raised LDL level cause
- engulfed by macrophages forming foam cells which accumulate in intima to give fatty streak
- develops into atherosclerotic plaque
- grows and reduces lumen
- this can rupture to trigger a thrombosis
what are the treatments for hyperlipoproteinaemias
- reduce cholesterol and saturated fat intake
- increase fibre
- increase exercise
- reduce smoking
- statins
- bile salt sequestrants
what do statins do
inhibit HMG-CoA reductase which is used in the production of cholesterol
what do bile salt sequestrants do
bind to bile salts in the GI tract so they are egested. this means more cholesterol is needed to make bile salts
what can cholesterol tests measure
- total cholesterol level
- non HDL level
- LDL level
- HDL level
- triglyceride level
- ratio of total cholesterol to HDL
