Lipid Biochemistry Flashcards
is cholesterol hydrophobic or philic?
hydrophobic
are the majority of cholesterols esterified or not?
majority is esterifies…70%
where do you find the esterified cholesterol in lipoproteins?
on the interior of the lipoprotein and the unesterified is on the outside
what organ is in charge of cholesterol synthesis and what percent does it make?
liver makes close to 80% of it
give the rate limiting enzyme in cholesterol synthesis
HMG CoA reductase
what hormone increases the action of HMG CoA reductase?
insulin
intermediates in the synthesis of cholesterol can lead to 3 types of important molecules…name them
ubiquinone
signal transduction molecules like Rho and Ras
complex glycoproteins
what is the name of the transcription factor that upregulates the production of HMG CoA reductase and the LDL receptor?
SREBP-2
what molecule is in charge of whether SREBP-2 is transcribed?
SCAP
what two things can inhibit SCAP?
intracellular cholesterol and LDL cholesterol
if you inhibit SCAP…what happens to HMG CoA reductase and LDL receptors?
production drops because you have less SREBP-2
what are the two ways to get cholesterol in a cell?
synthesis and uptake
what are the two ways to rid of cholesterol from a cell?
either secrete as bile salt or store it
if you have high cholesterol diet..what happens to the LDL receptors on the cells?
they begin to disappear because of the loss of SCAP action and ultimate loss of SREBP-2
what is the enzyme that helps store cholesterol?
ACAT
what can cause ACAT to decrease its activity?
saturated fats…ACAT uses PUFA to help store cholesterol by esterifying it…but with saturated fats it gets blocked
what two ways does saturated fat lead to high cholesterol?
blocks LDL receptors from working
blocks ACAT from storing cholesterol
what enzyme turns cholesterol into bile acids?
7a hydroxylase
what molecule has to attach to bile acids for them to be secreted?
fiber
what happens to bile acids on a low fiber diet?
the bile acids are not able to get secreted since no fiber and will travel back to the liver and be turned back into cholesterol via enterohepatic circulation
name three roles of bile acids
- essential for fat digestion
- absorb fat vitamins
- eliminate cholesterol from body
what percent of bile acids are reabsorbed? and the percent that is not…what is it representative of?
almost 99%…the slight percent that is not is the only way to rid of cholesterol from the body
what is the role of lipoproteins?
to transfer triglycerides, phospholipids and cholesterol
order the four lipoproteins in increasing density
chylomicrons
VLDL
LDL
HDL
how is density of a lipoprotein related to size and triglyceride content?
inversely…larger the size lower the density
more triglyceride…lower the density
how is density of a lipoprotein related to protein and phospholipid content?
directly…more protein means higher density
what is the role of apoprotein C?
it activates lipoprotein lipase
where is apoprotein C found?
mainly in peripheral tissues…like endothelial cells
what is the role of lipoprotein lipase?
to break up the lipoproteins and take off triglycerides around the tissues that will be able to store the triglycerides
where are apoproteins B and E found and what is their role?
they are found at the liver and help get LDL and IDL back into the liver
what lipoprotein is made and released by the liver
VLDL
what are the two sources of cholesterol/tricglycerides for the peripheral tissue?
chylomicrons from diet and VLDL from liver
at the peripheral tissue, what happens to VLDL and what does the peripheral tissue release back to the liver?
its triglycerides get clipped by lipoprotein lipase..apo C denpendent
then releases LDL and IDL to go back to the liver
what can nascent HDL do at peripheral tissue?
bind apoprotein A and pick up cholesterol…
if HDL picks up cholesterol at peripheral tissue…what happens next?
LCAT esterifies the cholesterol in HDL
what is the role of CETP in HDL molecules?
it can change cholesterol into VLDL, LDL or IDL or chylomicrons
after HDL has picked up cholesterol from periphery and then let it get turned into LDL/IDL/VLDL/chylomicrons..what happens to the HDL and remnants of cholesterol?
they get internalized and destroyed at the liver
what lipoprotine drives cholesterol from periphery to the liver?
HDL!!
what molecule takes the longest to be picked up by periphery or liver?
LDL…hence why we measure LDL in blood
