Term
Lipid Transport Is Protein Mediated |
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Definition
Albumin- produced by the liver, coagulable by heat; serum albumin aid in transport
of a variety of water insoluble molecules
Lipoproteins-produced in liver and intestine and serve in transport of triglycerides,
phospholipids and cholesterol
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Term
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Definition
Lipoproteins are complexes of lipids and proteins that transport lipids through the aqueous environment of the serum plasma
•nonpolar lipids (e.g. triglycerides and cholesterol esters) are carried in core of lipoprotein particles
•more polar lipids (e.g. phospholipids and free cholesterol) and the apolipoproteins form a surface monolayer around the lipoprotein core
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Term
Why have a protein component of lipoproteins?
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Definition
I. Structural integrity.
II. Mediate cellular lipoprotein uptake.
Cellular receptors bind the protein component.
III. Regulate enzymatic activity.
Mediate transfer of lipids to cells or
other lipoproteins.
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Term
Apoproteins.....Function? |
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Definition
-Apoproteins Provide Structural Integrity
-Apoproteins can serve as ligands for cellular lipoprotein receptors
-Apoproteins serve as activators of enzymes involved in lipid metabolism/transfer
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Term
Multiple Flavors of Lipoprotein
Classified by Density |
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Definition
Chylomicrons and Chylomicron remnants
Very Low Density Lipoprotein (VLDL)
Intermediate Density Lipoprotein (IDL)
Low Density Lipoprotein (LDL)
High Density Lipoprotein (HDL)
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Term
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Definition
•Lipids are transported through the body in the form of lipoproteins.
•Apoproteins are the protein component of lipoproteins and provide structural stability, mediate cellular lipoprotein uptake and serve as activators of plasma enzymes involved in lipid metabolism.
•Lipoproteins vary in density (VLDL, LDL IDL, and HDL) constituent protein and function.
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Term
Common Features of endogenous and exogenous Transport Pathways |
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Definition
I. Lipoproteins are produced by cells and delivered to the vascular system by exocytosis. Mucosal Cells of Small Intestine make chylomicrons using apoprotein B-48, triglycerides, phospholipids and cholesterol.
Liver Cells make VLDL using apoportein B-100, triglycerides phospholipids and cholesterol.
II. Nascent lipoproteins acquire small regulatory apoproteins (apoprotein E and apoprotein CII) from circulating HDL.
III. Remnant lipoproteins are taken up by receptor mediated endocytosis primarily by the liver.
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Term
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Definition
Lipoprotein lipase is secreted from muscle or adipose cells and transported across the endothelial cell of the capillary, where it binds to a glycoprotein on the the endothelial cell surface.
ApoC-II on the surface of the chylomicron activates the lipoprotein lipase.
Lipoprotein lipase catalyzes the hydrolysis of the triglycerides in the chylomicron to free fatty acids, converting the chylomicron into an chylomicron remnant.
Free fatty acids are taken up by the adipose and muscle cells, where they are esterified and stored as intracellular triglycerides.
Glycerol diffuses freely across the adipose cell membrane but is not utilized because of a lack of glycerol kinase. The glycerol diffuses to the liver where it is phosphorylated and ultimately converted into glucose 6-phosphate.
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Term
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Definition
-are formed from catabolism of chylomicrons
-are taken up by the liver and degraded
-ApoE is required for the binding of chylomicron remnant to chylomicron remnant receptors
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Term
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Definition
-are synthesized by the liver and receive regulatory apoproteins from HDL
- Lipoprotein lipase converts triglycerides in VLDLs to free fatty acids
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Term
mRNA editing to make apoB-100 and
apoB-48 |
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Definition
•Single gene encodes both proteins
•In the liver, the apoB-100 mRNA is translated directly to produce the apoB-100 protein found in VLDL, IDL, and LDL particles.
•In the intestinal mucosal cells, the apoB-100 mRNA is edited prior to translation. This editing step involves the conversion of a cytosine to a uracil, creating a new stop codon in the mRNA sequence. Translation of this mRNA produces apoB-48, an apoprotein that is identical to the amino-terminal portion of apoB-100, but does not contain the carboxyl-terminal portion of apoB-100.
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Term
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Definition
•IDL does not contain apoC-II, so the activity of lipoprotein lipase is lower when IDL is the substrate than when VLDL is the substrate
•40-60% of IDL particles produced are taken up by the liver and recycled, the remainder are converted to low density lipoprotein (LDL) particles
•LDL particles are cholesterol-rich and triglyceride-poor relative to IDL and VLDL particles
•under normal conditions, most of the cholesterol found in the plasma is in the LDL particles
•apoE is crucial for both the direct removal of IDLs and the conversion of IDLs to LDLs
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Term
LDL clearance by the liver is slow compared to clearance of other lipoproteins |
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Definition
lipoprotein half-life in plasma
VLDL (large) >30 minutes
VLDL (small) 1-3 hours
IDL 1-3 hours
LDL 2-3 days
•the slower clearance of IDLs and LDLs from the plasma is due to lower amounts of apoE
•the slow clearance of the LDLs enables it to gain access to all tissues and lymphatics except the brain (due to the tight blood-brain barrier)
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