Complex Lipids & Cholesterol Biochemistry Flashcards
Cholesterol concentration is highly regulated in the ____________.
liver cells
____________ synthesize cholesterol.
Hepatocytes
In addition to synthesis, hepatocytes can also get cholesterol from ______________.
diet, HDL, and LDL
There is both cholesterol and cholesteryl esters. Where is each found and why?
Cholesterol: more soluble and so found in lipid membranes
Cholesteryl ester: less soluble and so found in plaques and other aggregates
Trace the cholesterol synthesis pathway.
2 x acetyl co-a (Thiolase) Acetoacetyl co-a (HMG co-a synthase) HMG co-a (HMG co-a reductase) ***REGULATED STEP; USES 2 NADPH*** Mevalonic acid Isopentenyl pyrophosphate Geranyl pyrophosphate Farnesyl pyrophosphate Squalene Lanosterol Cholesterol
Expression of HMG co-a reductase is controlled by ___________.
SREBP, which is a protein that binds SRE (the region of DNA that encodes for HMG co-a)
How is SREBP controlled?
It is sequestered in the Golgi. When cholesterol is high, SREBP is prevented from leaving the ER. When cholesterol is low, SREBP is allowed to leave the ER and promote synthesis of HMG co-a reductase by binding to the SRE gene.
What does Dr. Bessesen want us to know about phospholipids?
Be able to recognize their names (like phosphatidylserine) and know that they are made from a glycerol backbone.
Glycolipids have a _____________ backbone.
ceramide
Where are glycolipids prominent?
In the nervous system (such as cerebroside)
Deficiencies in ___________ will produce accumulation of lipids in the nervous system.
lysosomal hydrolase
Cholesterol is a precursor for vitamin _____ in addition to bile acids and steroid hormones.
D
How much cholesterol do people typically eat per day?
300 - 600 mg (we synthesize about 1,000 mg)
HMG co-a is synthesized from ___________.
acetyl co-a
Other than cholesterol levels in the cytosol of hepatocytes, what additional mechanism regulates HMG co-a reductase?
Insulin increases its transcription and glucagon decreases its transcription.
