What is the pathway of cholesterol synthesis?

Cholesterol is synthesized via a cascade of enzymatic reactions known as the mevalonate pathway. This series of reactions is primarily regulated by a rate-limiting step involving the conversion of hydroxyl-methyl glutaryl-coenzyme A (HMG-CoA) into mevalonate.

What are the main routes by which cholesterol leaves the liver?

Cholesterol is excreted from the body via the bile either in the unesterified form or after conversion into bile acids in the liver. Coprostanol is the principal sterol in the feces; it is formed from cholesterol by the bacteria in the lower intestine.

How cholesterol is metabolized by the liver?

Cholesterol is oxidized by the liver into a variety of bile acids. These, in turn, are conjugated with glycine, taurine, glucuronic acid, or sulfate. A mixture of conjugated and nonconjugated bile acids, along with cholesterol itself, is excreted from the liver into the bile.

What is the route of absorption of cholesterol?

Cholesterol absorption begins in the stomach when dietary constituents are mixed with lingual and gastric enzymes. The stomach also functions to regulate the delivery of gastric chyme to the duodenum, where it is mixed with bile and pancreatic juice. This process continues within the lumen of the small intestine.

Which of the following is the major point of regulation on the pathway to cholesterol?

Explanation: HMG co-A reductase is the major point of regulation on the pathway to cholesterol.

Where does mevalonate pathway occur?

In higher plants, the MEP pathway operates in plastids while the mevalonate pathway operates in the cytosol. Examples of bacteria that contain the MEP pathway include Escherichia coli and pathogens such as Mycobacterium tuberculosis.

How does the liver take HDL?

In the third, free cholesterol may be taken up directly by the liver. Finally, HDL cholesterol esters may be selectively taken up via the scavenger receptor SR-B1. If the hepatic uptake of VLDL and IDL is impaired, their cholesterol may be delivered back to peripheral tissues.

Does liver have HDL receptors?

Scavenger receptor B1, the HDL receptor, is expressed abundantly in liver sinusoidal endothelial cells. Sci. Rep. 6, 20646; doi: 10.1038/srep20646 (2016).

How does it regulate de novo cholesterol synthesis in the liver?

Cholesterol synthesis is regulated at the step involving HMG-CoA reductase. The enzyme activity is regulated at the transcriptional level, that is, by changing the rate of synthesis of the mRNA encoding the enzyme. HMG-CoA reductase is regulated by phosphorylation and dephosphorylation also.

How does dietary cholesterol regulate de novo synthesis in the liver?

The amount of cholesterol that is synthesized in the liver is tightly regulated by dietary cholesterol levels. When dietary intake of cholesterol is high, synthesis is decreased and when dietary intake is low, synthesis is increased. However, cholesterol produced in other tissues is under no such feedback control.

What are the three stages of cholesterol synthesis?

A series of reactions – oxidation, cyclization, and loss of three methyl groups – results in conversion of squalene to cholesterol.

What does the isoprenoid pathway produce?

The pathway produces two five-carbon building blocks called isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP), which are used to make isoprenoids, a diverse class of over 30,000 biomolecules such as cholesterol, vitamin K, coenzyme Q10, and all steroid hormones.