Lipoproteins and Lipid Metabolism Flashcards
What is the rate-limiting step in cholesterol synthesis?
HMG CoA reductase
cholesterol are neutral, polar molecules which serve as precursors for steroid hormones, vitamin ___, and ___ salts.
cholesterol are neutral, polar molecules which serve as precursors for steroid hormones, vitamin D, and bile salts.
Lipoproteins are high molecular weight, water-soluble complexes of lipid and proteins with a___ core, __ surface. They are characterized by ___.
hydrophobic core hydrophilic surface characterized by density: HDL is high density, LDL is low density
What are apolipoproteins?
Proteins that bind lipids to form lipoproteins, transport the lipids through the lymphatic and circulatory systems. They serve to solubilize lipid and regulate size of lipoprotein
1 single Apolipoprotein B-48 is found on each ___
chylomicron
What is the only protein on LDL? What other two lipoproteins is it on?
B-100 A single one per VLDL/IDL/LDL
When an enterocyte absorbs a fatty meal, what are the things that happen within the cell?
- synthesis of triglycerides and phospholipids 2. in ER lumen, Apo-B containing lipoproteins are formed (B is intrinsic, can’t exchange off like other types of apolipoproteins) 3. apoliporotein glycosylation 4. exocytosis: chylomicrons to lymph
What is LPL, and where is it expressed?
Lipoprotein Lipase. Expressed on luminal surface of capillary endothelium; expressed by myocytes and adipocytes, secreted, and attached to luminal surface of overlying endothelium
It encounters the chylomicrons and breaks them down.
Where do chylmoicron remnants go? What do they acquire as they are catabolized into remnants?
Acquire apoE
the remnants are TG-poor, relatively enriched in CE, PL (?)
How do cells import cholesterol? Where are the majority of these receptors?
Apo-B-100/E receptor: LDL-R
mostly on hepatocytes.
Apo-B-48 includes the N-terminal 48% portion of this, and won’t bind to LDL-R, so the binding domain is in teh C-terminal portion of apo B
Aside from LDL-R, how else do cells import cholesterol? How do they differ?
LRP: LDL-receptor related protein: ApoE receptor (remnant receptor)
expresed on macrophages, VSMC, liver, brain, and placenta.
unlike LDL-R, has broad specificity, and doesn’t downregulate expression in response to cholesterol loading
In contrast to the exogeneous lipid pathway, which efficientyl trasnports dietary TGs to peripheral tissues, cholesterol to liver, and fat soluble vitamins from cut to tissues, eventually liver…what does the endogenous lipid pathawy do?
transports TGs synthesized in liver to the peripheral tissues, cholesterol from liver to peripheral tissues
what are the lipid profiles of ApoE-/- and LDL-R-/- knockout mice?
When LDL binds to LDL-R, what happens?
LDL endocytosis, acidfication of endosome puts makes the LDL separate, it degrades in lysosome to amino acids and cholesterol, which moves into the cell and regulates transcription of LDL receptor gene. Receptor recycles.
Name a transcription factor that translocates to the nucleus to cause activation of transcription of HMG CoA synthase and HMG CoA reductase. What does it bind to?
SREBP-2: Sterol Response Element Binding Protein 2
binds to SRE
What is Insig?
It mediates the SREBP moving to nucleus in times of low cholesterol.
In times of low cholesterol, Scap escorts SREBP from ER to Golgi, where it is cleaved and then can go to nucleus. In times of high cholesterol, Insig binds to Scap and prevents this from happening.
