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43 Cards in this Set
- Front
- Back
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What is the rate limiting step in Cholesterol synthesis?
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HMG CoA ---> Mevalonic Acid catalized by HMG CoA Reductase.
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What is the difference between Cholesterol and Cholesterol Ester? Why does it matter?
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Cholesterol + one free fatty acid = Cholesterol Ester (CE).
CE is the storage form of cholesterol in cells. |
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What step in Cholesterol synthesis do statins inhibit?
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The Rate Limiting Step: HMG CoA --> Mevalonic Acid by HMG CoA Reductase.
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What tissue makes cholesterol?
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All tissue synthesize cholesterol but 10-20% of cholesterol synthesis happens in the liver.
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HMG CoA Reductase:
What up-regulates the synthesis of HMG CoA Reductase? |
Low Cholesterol signals the Sterol Regulatory Element-Binding Protein (SREBP) to travel to the nucleus and increase the transcription of the HMG CoA Reductase gene.
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HMG CoA Reductase:
What increases the activity of HMG CoA Reductase? |
Insulin via Protein Phosphatase. So, it is more active when de-phosphorylated.
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HMG CoA Reductase:
What decreses the activity of HMG CoA Reductase? |
Increased cholesterol decreases protein stability.
Also, phosphorylation of enzyme decreases its activity. |
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Trace a cholesterol molecule in the liver to Micelle formation in the gut.
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Cholesterol --> Bile Acid --> Bile Salt --> GI --> Micelle formation.
The first step is done in the liver by 7-Alpha-Hydroxylase. |
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What is the only significant mechanism for cholesterol excretion in the body?
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Bile salts. The liver must then synthesize more blie acids from cholesterol.
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Where do Chytomicrons (CM) form?
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Intestine
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The Chylomicron (CM) acquires two proteins in the blood stream. Which proteins are they? Who gives those proteins to the CM?
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ApoE and ApoCII.
HDL gives the CM in the blood stream those two proteins. |
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Why are ApoE and ApoCII needed in the CM/CM-Remnants?
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ApoE is needed because it is recognized by LDL-R Related Protein receptor in the liver.
ApoCII is needed because it is a co-factor for Lipoprotein Lipase (LPL) which degrades TC. |
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Which protein is unique to the Chylomicron/CM-Remnant?
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Apo48
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Which lipoprotein has the highest percentage of Triglycerides?
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CM
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Which lipoprotein has the lowest percentage of Triglycerides?
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LDL and HDL
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Which lipoprotein has the highest percentage of Cholesterol?
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LDL
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Which lipoprotein has the lowest percentage of Cholesterol?
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Chylomicron
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What is the goal of VLDL/IDL/LDL lipoproteins?
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To release contents into tissue.
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Where is VLDL made?
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In the liver.
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Which is the main protein of VLDL?
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ApoB100 which indicates that it was made in the liver.
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What proteins does VLDL acquire as it matures in the blood?
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ApoE and ApoCII, again donated by HDL.
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What is the purpose of ApoCII in VLDL?
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To activate LPL so that VLDL may turn into IDL.
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What makes up the bulk of VLDL?
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TG at 65%
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How does IDL become LDL?
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Two ways:
1) Further hydrolyzed by LPL and Hepatic Lipase (LP). 2) It also trades TG for CE with HDL via Cholesterol Ester Transfer Protein (CETP) |
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What is the fate of LDL?
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Delivers Cholesterol to tissues by endocytosis. The tissue recognizes ApoB100 or ApoE via LDL Receptor.
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Where do we find a lot of LDL-Receptors?
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Adrenal glands, gonads.
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What is a lipoprotein(a)?
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LDL with Apo(a) and ApoB100 liked together via a disulfide bond.
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Which proteins does the LDL-Receptor bind?
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ApoB100 and ApoE
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What controls the expression of LDL-R gene?
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SREBP
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Why does the LDL Receptor Related Protein does not bind LDL?
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Because LDL has lost its ApoE. It only has ApoB100. ApoB100 is not recognized by LDL Receptor Related Protein.
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What happens if there are mutations in the LDL-Receptor?
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LDL-Receptor binds ApoB100 &/or ApoE. So, it binds LDL. If it cannot bind LDL then the result would be high levels of LDL in the blood.
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Where is HDL made?
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In both liver and intestines.
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What is the goal of HDL?
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To take up free cholesterol from tissues to deliver it back to the liver.
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What does HDL do the free cholesterol?
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it turns it into Cholesterol Ester via LCAT.
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How can HDL transfer cholesterol back to liver?
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Via SRB1
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How can HDL transfer cholesterol to tissues other than liver?
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By trading Cholesterol for TG with LDL via CETransfer Protein.
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What happens to small and dense HDL particles?
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Get excreted by kidney
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Where do we find ApoA1? What is its purpose?
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Found in HDL.
It has many purposes: 1) structural protein 2) LCAT co-factor (LCAT converts free cholesterol into cholesterol ester) 3) Binds SR-B1 (to deliver CE to liver, adrenal glands, gonads.) |
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What is ABC1?
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Transports FC out of cells to be picked up by HDL
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why do we use a fasting blood sample for a lipid profile?
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To eliminate chylomicrons
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How do you estimate LDL?
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LDL = TG - ( HDL + [ TG / 5 ] )
Under condition that TG < 400 |
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What are five factors that can affect LDL blood levels?
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1) Increased VLDL synthesis
2) Down-regulation of LDLR 3) Increased ApoE-containing molecules that compete for LDLR 4) Defective or decresed expression of LDLR 5) Defective ApoB100 |
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What is the name of HMG CoA Reductase Inhibitors often prescribed?
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Statins
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