cholesterol Flashcards
what is cholesterol essential for? and why?
its essential for membranes
it helps them maintain the bilayers integrity and regulates its permeabiltiy
what is excess cholesterol associated with?
cardiovascualr disease
how many steps are there in the biosynthesis of cholesterol?
19 and the process uses a lot of energy so you know its an important molecule
what percentage of plasma cells are cholesterol?
> 35%
what is cholesterol a precursor to?
steroids
vitamins
bile salts
how is acetyl-CoA used in cholesterol synthesis? [hint- its a 3 step process]
the step involeves HMD-CoA-reductase enzyme
1. the synthesis of isopentyl pyrophosphate (via melanolvate)- these are the building blocks of cholesterol
2. condensation of 6 molecules of isopentyp pyrophosphate to form squalane
3. cyclicisation of squalane and further processing of cholesterol
how is cholesterol biosynthesis regulated?
by feedback regualtion- it depends on how much cellular cholesterol is present
regulation of HGM-CoA-reductase regulates cholesterol synthesis - this catalyses the committed step of cholesterol synthesis, regulates its amount and its activity
what are 4 ways that HGM-CoA is controlled?
- the rate if synthesis of HGM… into mRNA
- the rate of translation of HGM…mRNA into protein
- the rate of degradation of HGM… protein
- phosphorylation state of HGM…protein
what is the cholesterol sensor called?
SCAP
what is SREBP?
its the Sterol Regulatory Element Binding Protein
its actually a transcription factor (protein)
what happens when theres not enough cholesterol?
the SCAP goes into the golgi
where does the DNA bindign domain move to activate gene expression?
it moves ftom the ER into the golgi to regulate gene expression
what is SRE? and what does it do?
it stands for sterol regulatory element and it is the region of HGM-CoA reducatse gene that the DNA-binding domain of SREBP binds to
what are the steps of transcriptional regulation of HGM-CoA reductase?
the SCAP detects a fall in cholesterol levels then it goes to the golgi
then a 2 step cleavage process of SREBP causes it to bind to a DNA-binding domain to promote transcription of HGM-CoA reductase
what is the rate of translation of HGM-CoA reductase mRNA into protein inhibited by?
non-sterol metabolites derived from melanovate
what does the HGM-CoA reductase membrane domain do if it senses increasing levels of sterols?
it interacts indirectly with ubiquiting enzymes
HGM-CoA-reductase then becomes polyubiqutinated and is extracted form the membrane and degraded by the proteosome
how is cholesterol transported through the body?
in lipoprotein pariticles
what is the structure of lipoprotein particels?
theyve got hydrophobic lipid core surrounded by polar lipids and proteins
what do HDL and LDL mean?
high-density lipoprotein - this is the good cholesterol
low-density lipoprotein - this is the bad type of cholesterol
where are bile salts made and stored? (its different places)
they’re made in the liver but they’re stored in the gall bladder and then released into the small intestine
what are derivatives of cholesterol?
steroid hormones
bile salts
vitamin D
what is the technical name for statins?
theyre called HMG-Co-reductase inhibitors and asct as lipid lowering drugs to reduce cholesterol levels
