2.7 Cholesterol Synthesis Flashcards
Enzyme of first step of cholesterol synthesis
HMG CoA Reductase
KEY REGULATORY ENZYME
All three reactions of the first step in cholesterol synthesis
Acetyl CoA –> Acetoacetyl CoA
Acetoacetyl CoA –> HMG CoA
HMG CoA –> Mevalonate
2nd step in cholesterol synthesis
Mevalonate –> Formation of Isoprenoids
The two versions of isoprenoids
Isopentenyl Pyrophosphate
Dimethylallyl Pyrophosphate
Isoprenoids are the building blocks for what important molecule in electron transport chain
Ubiquinone
Outline third step of cholesterol synthesis
Condensation of Isoprene into Squalene (30 carbon molecule).
5+5=10 –> 10+5=15 –> 15+15=30
What occurs in the fourth step of Cholesterol Synthesis
Cyclization of Squalene to Lanosterol
What is the rate limiting step of Cholesterol Synthesis Pathway
HMG-CoA to Mevalonic Acid
What are the two paths of the intermediate HMG-CoA
- Cytosolic Pathway - HMG-CoA is used to make cholesterol
2. Mitochondrial Pathway - HMG-CoA is used to make Ketone Bodies
What enzyme catalyzes reaction of HMG CoA to Ketone BOdies
HMG-CoA Lyase
How is Cholesterol Synthesis regulated during High Cholesterol levels
SCAP sequesters SREBP in ER
How is Cholesterol Synthesis regulated in Low Levels of Cholesterol
SCAP and SREBP are moved to Golgi.
In Golgi, SCAP is released and SREBP is clipped and made small to go to nucleus. It then turns on SRE to transcribe HMG CoA-Reductase
What is the common intermediate for all 5 classes of steroids
Pregnolone
Name the 5 classes of steroids
Androgens, Estrogens, Progestagens, Glucocorticoids, Mineralocorticoids
How to synthesize phospholipids
Take phosphate group off of phosphatidate and add CDP. Then the head group can e added to form whatever form of Phospholipid
