Cholesterol

Question 1

This substance is an essential component of cell membranes and is a precursor to bile salts and steroid hormones.

Answer 1

Cholesterol

Question 2

Only about 30% of circulating cholesterol occurs in the free form. Most are what?

Answer 2

Esterified long chain fatty acids attached to hydroxyl groups

Question 3

This type of cholesterol is more hydrophobic, not located in membranes, transported by lipoproteins, and solubized in bile.

Answer 3

Esterified cholesterol

Question 4

What is the primary site of cholesterol production?

Answer 4

Liver, primarily in the cytosol

Question 5

What are raw materials needed for cholesterol synthesis?

Answer 5

ACETYL CoA
-Oxidation of long-chain fatty acids (OHOT)
-Oxidation of pyruvate (glycolysis)
-Oxidation of ketogenic amino acids
NADPH and ATP

Question 6

What is the rate limiting, key regulatory step of cholesterol synthesis?

Answer 6

HMG CoA reductase

Question 7

What does HMG CoA reductase create?

Answer 7

Mevalonate, which is the first unique compound in cholesterol synthesis

Question 8

When is HMG CoA reductase active? Inactive?

Answer 8

• Active when non-phosphorylated

- Inactive when phosphorylated

Question 9

Where are bile acids/salts primarily made?

Answer 9

• In the liver and secreted into the duodenum

- Can also be made in the intestines

Question 10

In simple terms, what is the process of cholesterol synthesis?

Answer 10

• Eat carbohydrate
• Muscle and liver are full of energy and glycogen
• Glucokinase pushes glycolysis forward (liver)
• Prep step runs
• Start the Kreb’s cycle
• Citrate is kicked out (high energy charge)
• Citrate lyase gives back the acetyl CoA
• Make fat and cholesterol

Question 11

Is there degradation of cholesterol?

Answer 11

No

Question 12

What is cholesterol synthesis stimulated by?

Answer 12

ATP, NADH, Insulin, and Fructose

Question 13

What is cholesterol synthesis inhibited by?

Answer 13

ADP, AMP, NAD+, and glucagon

Question 14

These are competitive inhibitors of HMG CoA reductase.

Answer 14

Statins

Question 15

Which hormones upregulate HMG CoA reductase? Downregulate?

Answer 15

• Insulin and thyroxine upregulate

- Glucagon and glucocorticoids downregulate