Cholesterol and Cholesterol Esters Review Flashcards
What is mevalonate?
Mevalonate is an important intermediate in cholesterol biosynthesis.
What reaction generates mevalonate?
The reaction generated by HMG-CoA reductase.
Why do we care about HMG-CoA reductase?
The reaction catalyzed by HMG-CoA reductase is the limiting enzyme in cholesterol biosynthesis
What drug targets HMG-CoA reductase?
Statins
What electron carrier is necessary for the synthesis of cholesterol?
NADPH! It is oxidized to NADP+ in the conversion of HMG-CoA to mevalonate
What is an important regulator of HMG-CoA reductase?
Cholesterol- the end product of cholesterol synthesis negatively feeds back to inhibit HMG-CoA reductase activity.
What enzyme is responsible for the conversion of cholesterol into a cholesterol ester?
ACAT: Acyl-CoA cholesterol acyl-transferase
What is the purpose of cholesterol esters?
Cholesterol esters make storage of cholesterols in LDLs and VLDLs etc more efficient.
Cholesterol esters = storage
What is the enzyme responsible for regulating the conversion of cholesterol to bile acids?
7-alpha hydroxylase
How does increased cholesterol affect HMG-CoA reductase?
HMG-CoA reductase is inhibited.
Remember: cholesterol negatively feedsback onto HMG-CoA reductase to inhibit it’s activity (no cholesterol synthesis is needed)
How does high levels of cholesterol affect the activity of ACAT and 7-alpha-hydroxylase?
They are both activated. ACAT is responsible for the esterification of cholesterol for storage, and 7-alpha-hydroxylase is responsible for the production of bile acids (high cholesterol indicates food intake –> bile salts are needed for digestion)
Where in the cell is HMG-CoA synthase?
Only in the mitochondria.
HMG-CoA synthase
