Quiz 3 Cholesterol Synthesis Flashcards
Nearly all tissues can synthesize cholesterol from what?
Acetyl CoA
20% of cholesterol synthesis happens where?
In the liver
Extrahepatic sites cholesterol can be synthesized?
Intestine, adrenal cortex, reproductive tissues
Chylomicron remnants go to where and converted to bile salts?
liver
Free cholesterol is an essential component of what?
cell membranes (this regulates the fluidty, gives strength to the membrane)
Free cholesterol is precursor to?
bile salts and steroid hormones
Type of cholesterol not located in membranes and is MORE hydrophobic?
esterfied cholesterol
What are two outcomes of excess cholesterol?
Gallstones and Atherosclerosis (cholesterol deposited at the linings of blood vessels)
30% of circulating cholesterol is this form?
Free cholesterol
Cholesterol Synthesis occurs where in the cell?
Cytosol
Reducing power of cholesterol synthesis?
NADPH
What things are required in cholesterol synthesis?
ATP, molecular O2, Acetyl CoA
What are the 3 stages of cholesterol synthesis?
Stage 1: 3 Acetyl CoA → HMG-COA
Stage 2: HMG-CoA → Mevalonic Acid (mevalonate) → Squalene
Stage 3: Squalene → Cholesterol
What is the rate-limiting, key regulatory step of cholesterol synthesis?
HMG-CoA reductase (remember this occurs in the cytosol)
Product of HMG-CoA Reductase?
Mevalonate (mevalonic acid)
Is HMG CoA reductase reversible or irreversible?
IRREVERSIBLE
As cholesterol concentration increases, what does this do to HMG CoA reductase?
Inhibits it (low cholesterol levels stimulate this enzyme)
HMG CoA reductase is active or inactive (inhibited) when phosphorylated by AMP-activated protein kinase?
Inhibited when phosphorylated (stimulated when non-phosphorylated)
Competitive inhibitors of HMG CoA reductase which block endogenous synthesis of cholesterol?
Statins
What type of bile salts are made in the liver and then secreted into the duodenum?
Primary bile salts
Which type of bile salts are made in the intestine?
Secondary bile salts
All bile salts end in?
Cholic acid or cholate
Difference in polar and non polar bile salts?
Number and position of hydroxyl groups
What is the precursor for all steroid hormones?
Pregnenolone
