chylomicron assembly

Definition

Target type: biologicalprocess

The non-covalent aggregation and arrangement of proteins and lipids in the intestine to form a chylomicron. [GOC:BHF, GOC:mah]

Chylomicron assembly is a complex process that takes place in the intestinal epithelial cells, specifically in the enterocytes. It involves the packaging of dietary lipids, including triglycerides, cholesterol, and phospholipids, into lipoprotein particles called chylomicrons. These particles are then transported through the lymphatic system and eventually enter the bloodstream to deliver dietary lipids to tissues throughout the body.

The process begins with the digestion of dietary fats by lipases in the small intestine. The resulting fatty acids and monoglycerides are then absorbed into the enterocytes. Inside the enterocytes, these lipids undergo re-esterification, forming triglycerides again.

Chylomicron assembly is facilitated by several key proteins:

* **Microsomal triglyceride transfer protein (MTP):** This protein transfers triglycerides from the endoplasmic reticulum to nascent chylomicrons, playing a critical role in their assembly.
* **Apoprotein B-48 (ApoB-48):** This protein serves as the structural backbone of chylomicrons. It anchors the lipid core and facilitates the binding of other apolipoproteins.
* **Apolipoprotein AI (ApoAI):** This protein is associated with high-density lipoprotein (HDL) but is also found in chylomicrons. It plays a role in the activation of lipoprotein lipase (LPL), which breaks down triglycerides in the bloodstream.
* **Apolipoprotein C-II (ApoC-II):** This protein is a cofactor for LPL, enhancing its activity.

The assembly process can be summarized as follows:

1. **Lipid synthesis and packaging:** Triglycerides, cholesterol esters, and phospholipids are synthesized and packaged into lipid droplets within the enterocytes.
2. **ApoB-48 synthesis and association:** ApoB-48 is synthesized in the endoplasmic reticulum and associates with the lipid droplets.
3. **MTP-mediated triglyceride transfer:** MTP transfers triglycerides from the endoplasmic reticulum to the ApoB-48-containing lipid droplets, leading to the formation of nascent chylomicrons.
4. **Addition of other apolipoproteins:** ApoAI, ApoC-II, and other apolipoproteins are added to the nascent chylomicrons, completing their assembly.
5. **Exocytosis and transport:** The mature chylomicrons are released from the enterocytes via exocytosis and enter the lymphatic system.
6. **Entry into bloodstream:** From the lymphatic system, chylomicrons enter the bloodstream and circulate to deliver dietary lipids to various tissues.
7. **Lipoprotein lipase action:** LPL, activated by ApoAI and ApoC-II, hydrolyzes triglycerides in chylomicrons, releasing free fatty acids that can be taken up by tissues.

The process of chylomicron assembly is crucial for the delivery of dietary lipids to tissues. It ensures that absorbed fats are transported efficiently and reach their destinations to provide energy and support cellular functions.'
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Proteins (2)

Compounds (5)