Transport of fats Flashcards
What are the general components of a lipoprotein?
The shell is made of apoproteins, phospholipids, and unesterified cholesterol
What is the general change in composition of lipoproteins as they increase in density?
They tend to become smaller; and have increased levels of cholesterol and protein relative to triacylglycerides
Where are the ApoB-48 proteins found and what is the difference between it and the ApoB-100?
They exist mainly on chylomicrons; their RNA transcripts are edited to introduce a stop codon that eliminates the LDL receptor binding region
Which lipoproteins have ApoB-100 on their surfaces?
VLDL, IDL, and LDL
What is the role of lipoprotein lipase? Where is it found?
It exists on capillary endothelium of muscle cells, adipose tissue and active mammary gland cells; when activated by Apo-CII, it will release fatty acids from TAGs and absorb them
What is the role of ACAT?
It esterifies cholesterol that comes into cells from the lipoproteins
What is the role of LCAT?
It is found on HDLs and converts cholesterol remnants in chylomicrons and VLDL to cholesterol esters for transport. Needs ApoA-1
What is the role of CETP?
It will transfer TAG and cholesterols between lipoproteins
What is the transport role of chylomicrons?
They ferry TAGs to adipocytes
What is the transport role of VLDL and LDL?
They ferry TAGs and cholesterol respectively from the liver to the peripheral tissues
What is the transport role of HDLs?
They will ferry excess cholesterol from the periphery to the liver
What are the main apoproteins on chylomicrons?
ApoB-48, ApoE, ApoC-II
What apoproteins are commonly found on VLDL, IDL, and LDL?
ApoB-100, ApoC-II (VLDL and IDL have Apo-E)
How do VLDLs become converted to other types of carriers?
As they lose their fatty acids, they gain density and become IDLs; as IDL lose their ApoE proteins they become LDLs
How are LDLs processed by peripheral cells?
Instead of taking fatty acids out of the lipoprotein, the cell engulfs the whole packed through the LDL receptor and conjugates the cholesterol components with oleic acid
How does familial hypercholesterolemia occur?
Genetic mutations in the LDL receptors prevent the individual from absorbing LDLs
How do HDLs morphologically change over the course of their jobs?
They start out discoid when they are empty and as they fill they become spheroid
How do HDLs lose their acquired cholesterols?
They bind to the SR-B1 receptor on the liver surface and cholesterol is extracted
How the LDLreceptor gene regulated?
The SREBP system also controls transcription of the receptor; if cholesterol levels in the cell are high, then the receptor will be downregulated
What percentage of bile salts are recycled daily?
95%; the 5% that is excreted is the body’s main way of eliminating cholesterol
How is cholesterol converted to a bile salt?
A cytochrome P-450 enzyme, cholesterol-7-alpha-hydroxylase uses oxygen to introduce polarity to cholesterol.
How are bile acids conjugated?
They are transformed to strong acids by addiition of glycine or taurine to the carboxylic acid region of the bile acid
How is bile salt synthesis regulated?
High serum cholesterol levels promote upregulation of the 7-alpha-hydroxylase; high bile salt levels inhibit transcription
What are desired, borderline, and high levels of serum cholesterol?
Desired is less than 190 mg/dL; borderline is 200-240 mg/dL; High is in excess of 240 mg/dL
What are optimal targets for LDL and HDL levels?
LDL levels should be 100-129 mg/dL; HDL levels should be around 50 mg/dL
How can ApoE be correlative with Alzheimer’s risk?
Patients who are homozygous for the E4 variant have a much higher risk of developing late onset Alzheimers
