Biosynthesis of Cholesterol

These flashcards cover key concepts related to cholesterol biosynthesis, metabolism, and regulation as discussed in the lecture.

What are the two primary functions of cholesterol in the body?

Cholesterol serves as a component of cell membranes and is a precursor for bile acids, steroid hormones, and Vitamin D.

What are the major disorders associated with cholesterol metabolism?

Cardiovascular disease and gall stones.

Where is the main site of cholesterol synthesis in the body?

The liver.

What percentage of cholesterol is synthesized in the body compared to dietary sources?

Approximately 70% is synthesized in the body, and about 30% comes from diet.

What is the energetic cost in moles for producing cholesterol?

18 moles of acetyl CoA, 18 moles of ATP, and 16 moles of NADPH are required.

What is the first step in the synthesis of cholesterol?

Acetyl-CoA is converted to HMG-CoA, then to Mevalonate.

What enzyme is responsible for the regulatory step in cholesterol synthesis?

HMG-CoA Reductase.

What are the coenzymes involved in the first stage of cholesterol synthesis?

NADPH.

What is the final isoprenoid compound formed from mevalonate?

Farnesyl pyrophosphate.

Which enzyme synthesizes Squalene from farnesyl pyrophosphate?

Squalene Synthase.

What does Squalene convert to in the next stage of cholesterol synthesis?

Lanosterol.

What are the regulators that influence HMG-CoA Reductase activity?

Insulin and Thyroid hormones increase activity; Glucagon and Cortisol decrease it.

What are statin drugs used for?

Statin drugs inhibit HMG-CoA Reductase to lower cholesterol levels.

Which dietary sources are significant for cholesterol?

Eggs, meat, and milk.

What happens to cholesterol in the human body?

Cholesterol cannot be digested; it is excreted in feces, mainly as bile acids.

How much bile acids are produced daily and reabsorbed?

30 g of bile acids are produced daily, with up to 98% being reabsorbed.

What factors can increase intracellular free cholesterol concentration?

De novo biosynthesis, dietary cholesterol intake, and receptor-mediated uptake of LDL.

What is the role of bile acids in fat digestion?

Bile acids assist in the digestion and absorption of dietary fats.

What is observed in guinea pigs with vitamin C deficiency regarding cholesterol?

Cholesterol accumulation and atherosclerosis due to decreased bile acid production.

What lifestyle effects are known to elevate blood cholesterol levels?

High blood pressure, smoking, abdominal obesity, and lack of exercise.

What are primary bile acids synthesized from?

Cholesterol.

What class of drugs is known to lower cholesterol?

Statin drugs.

What is the relationship between cholesterol and steroid hormone synthesis?

Cholesterol is converted into various steroid hormones like progesterone and testosterone.

How many grams of cholesterol is typically eliminated in feces per day?

1 gram of cholesterol is eliminated in the feces.

What is the proposed mechanism of oat bran reducing LDL cholesterol?

Oat bran binds cholesterol and bile acids, promoting their excretion.

What are the two primary bile acids produced in the liver from cholesterol?

Cholic acid and chenodeoxycholic acid.

What is one significant way cholesterol is regulated in the body?

By the activity of HMG-CoA reductase, which is regulated by hormones and cholesterol levels.

What dietary recommendations might help lower cholesterol levels?

Increasing vitamin C intake and incorporating oat bran into the diet.

What is the circulatory route for reabsorbed bile acids?

They enter the enterohepatic (portal) circulation.

What is a common effect of high dietary cholesterol on cholesterol synthesis?

Increased dietary cholesterol intake can lead to decreased synthesis of body cholesterol.