cholesterol catabolic process

Definition

Target type: biologicalprocess

The chemical reactions and pathways resulting in the breakdown of cholesterol, cholest-5-en-3 beta-ol, the principal sterol of vertebrates and the precursor of many steroids, including bile acids and steroid hormones. [GOC:ai]

Cholesterol catabolism is a complex process that involves the breakdown of cholesterol into bile acids, a process essential for the digestion and absorption of fats. It begins in the liver, where cholesterol is first converted into **bile acid intermediates** through a series of enzymatic reactions.

These intermediates are then transported to the gallbladder, where they are stored and concentrated. When fats are ingested, the gallbladder releases bile acids into the small intestine, where they emulsify fats, breaking them down into smaller particles that can be more easily digested and absorbed by the body.

The process of cholesterol catabolism can be divided into two main phases:

**Phase 1: Conversion of cholesterol to bile acid intermediates:**
1. **7α-hydroxylation:** Cholesterol is first hydroxylated at the 7α position by the enzyme **CYP7A1**, the rate-limiting enzyme in bile acid synthesis. This reaction is crucial for initiating the conversion of cholesterol into bile acids.
2. **Further modifications:** The 7α-hydroxycholesterol is further modified by a series of enzymes, including **CYP8B1**, **CYP27A1**, and **CYP7B1**, to produce **bile acid intermediates** like **cholic acid** and **chenodeoxycholic acid**.

**Phase 2: Conjugation of bile acid intermediates:**
1. **Conjugation:** The bile acid intermediates are then conjugated with **glycine** or **taurine**, which increases their water solubility and facilitates their excretion in the bile.
2. **Excretion:** The conjugated bile acids are excreted in the bile, where they travel to the small intestine to aid in fat digestion.
3. **Reabsorption:** Some of the bile acids are reabsorbed in the ileum and transported back to the liver, completing the **enterohepatic circulation**.

The regulation of cholesterol catabolism is complex and involves various factors, including dietary cholesterol levels, hormones like **insulin**, and the expression of key enzymes involved in the process.

In summary, the cholesterol catabolic process is essential for the digestion and absorption of fats, the removal of excess cholesterol from the body, and the maintenance of overall health. Any dysfunction in this pathway can lead to health issues such as **gallstones** and **high cholesterol levels**. '
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Proteins (2)

Compounds (7)