cholesterol

Question 1

what is cholesterol essential for? and why?

Answer 1

its essential for membranes
it helps them maintain the bilayers integrity and regulates its permeabiltiy

Question 2

what is excess cholesterol associated with?

Answer 2

cardiovascualr disease

Question 3

how many steps are there in the biosynthesis of cholesterol?

Answer 3

19 and the process uses a lot of energy so you know its an important molecule

Question 4

what percentage of plasma cells are cholesterol?

Answer 4

> 35%

Question 5

what is cholesterol a precursor to?

Answer 5

steroids
vitamins
bile salts

Question 6

how is acetyl-CoA used in cholesterol synthesis? [hint- its a 3 step process]

Answer 6

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

Question 7

how is cholesterol biosynthesis regulated?

Answer 7

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

Question 8

what are 4 ways that HGM-CoA is controlled?

Answer 8

1. the rate if synthesis of HGM… into mRNA
2. the rate of translation of HGM…mRNA into protein
3. the rate of degradation of HGM… protein
4. phosphorylation state of HGM…protein

Question 9

what is the cholesterol sensor called?

Answer 9

SCAP

Question 10

what is SREBP?

Answer 10

its the Sterol Regulatory Element Binding Protein
its actually a transcription factor (protein)

Question 11

what happens when theres not enough cholesterol?

Answer 11

the SCAP goes into the golgi

Question 12

where does the DNA bindign domain move to activate gene expression?

Answer 12

it moves ftom the ER into the golgi to regulate gene expression

Question 13

what is SRE? and what does it do?

Answer 13

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

Question 14

what are the steps of transcriptional regulation of HGM-CoA reductase?

Answer 14

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

Question 15

what is the rate of translation of HGM-CoA reductase mRNA into protein inhibited by?

Answer 15

non-sterol metabolites derived from melanovate

Question 16

what does the HGM-CoA reductase membrane domain do if it senses increasing levels of sterols?

Answer 16

it interacts indirectly with ubiquiting enzymes
HGM-CoA-reductase then becomes polyubiqutinated and is extracted form the membrane and degraded by the proteosome

Question 17

how is cholesterol transported through the body?

Answer 17

in lipoprotein pariticles

Question 18

what is the structure of lipoprotein particels?

Answer 18

theyve got hydrophobic lipid core surrounded by polar lipids and proteins

Question 19

what do HDL and LDL mean?

Answer 19

high-density lipoprotein - this is the good cholesterol
low-density lipoprotein - this is the bad type of cholesterol

Question 20

where are bile salts made and stored? (its different places)

Answer 20

they’re made in the liver but they’re stored in the gall bladder and then released into the small intestine

Question 21

what are derivatives of cholesterol?

Answer 21

steroid hormones
bile salts
vitamin D

Question 22

what is the technical name for statins?

Answer 22

theyre called HMG-Co-reductase inhibitors and asct as lipid lowering drugs to reduce cholesterol levels