Lipoproteins Flashcards
Describe the life cycle of VLDLs.
VLDLs are formed in the liver with ApoB100. They interact with HDL in the blood to obtain ApoC-II & ApoE. APOC-II activated LPL to degrade triglycerides to FAs to be taken up by tissues. VLDLs return ApoC-II & ApoE to HDLs and become LDLs. They are taken up into peripheral tissues via ApoB100.
Describe the life cycle of chylomicrons.
Chylomicrons are synthesized in the small intestine. ApoB48 protein is required for secretion into the bloodstream. They interact with HDL in the blood to obtain ApoC-II & ApoE. APOC-II activated LPL to degrade triglycerides to FAs to be taken up by tissues. Chylomicron remnants are taken up by the liver via ApoE.
What disease is associated with a deficiency in ABCA1?
Tangier Disease - inability to remove cholesterol from tissues causing low HDL levels and accumulation of cholesterol in tissues
What is the effect of high cellular cholesterol levels on intracellular enzymes?
Free cholesterol within the cell inhibits LDL receptor synthesis to prevent over-uptake and the HMG-CoA Reductase to stop cellular cholesterol synthesis. It also stimulates the Acyl Coa Cholesterol Acyltransferase to produce cholesterol esters for storage.
What is the result of a deficiency in the absorption of fat, cholesterol, and fat-soluble vitamins by cells?
Hyperlipoproteinemia
What protein is responsible for transporting cholesterol from tissues to HDL for recycling in the liver?
ABCA1
What is the cause of Type II hyperlipoproteinemia?
Deficiency of the LDL receptor
Describe the life cycle of HDLs.
HDLs are formed in the liver with ApoA-I. They collect excess cholesterol from peripheral tissues to be returned to the liver for recycling.
What enzyme is activated by HDL to esterify cholesterol? How does HDL activate the enzyme?
ApoA-I on HDL activates Phosphatidylcholine Cholesterol
Acyltransferase to esterify cholesterol
What molecule induces Lipoprotein Lipase (LPL)? Does this same molecule activate the lipase?
Insulin induces LPL, however, ApoC-II activates the lipase in the capillary.
A deficiency in the ApoE protein causes what hyperlipoproteinemia?
Type III hyperlipoproteinemia
True/False. ApoB48 and ApoB100 are synthesized from the same gene.
True. ApoB48 is a shortened version of the ApoB100 gene. In the intestines, C is exchanged for U via RNA editing creating an early stop codon.
What is the cause of Type IV hyperlipoproteinemia?
Excess VLDL
What is the cause of Type I hyperlipoproteinemia?
Deficiency of ApoC-II
How is LDL taken up into the liver and peripheral tissues?
ApoB100 binds with a receptor on the cell surface. LDL is endocytosed in an endosome into the cell. The endosome becomes a lysosome that breaks down the LDL into amino acids and free cholesterol.
Describe lipoproteins in terms of composition, size, and density.
Chylomicrons are the largest, but least dense. They are composed primarily of triglycerides with some cholesterol esters.
VLDLs are smaller and denser than chylomicrons. They are composed of a 1:1 ratio of triglycerides:cholesterol esters.
IDLs are smaller and denser than VLDLs. They are composed of more cholesterol esters than triglycerides.
LDLs are smaller and denser than IDLs. They are composed of primarily cholesterol esters with some triglycerides.
HDLs are the smallest and densest lipoprotein. They are composed primarily of proteins.
