Cholesterol uptake by cells, outside of the liver, primarily occurs through receptor-mediated endocytosis of low-density lipoproteins (LDLs). Here's a breakdown:
LDL and Cholesterol Transport
- The liver plays a central role. It packages both dietary cholesterol and cholesterol it synthesizes itself into LDLs. These LDLs are then released into the bloodstream.
- LDLs act as cholesterol transporters, delivering cholesterol to cells throughout the body that need it.
Receptor-Mediated Endocytosis: The Uptake Process
Cellular uptake of LDL-cholesterol is a tightly regulated process:
-
LDL Receptor Binding: Cells have LDL receptors on their surface. These receptors specifically recognize and bind to the LDL particles in the blood.
-
Endocytosis: Once the LDL binds to the LDL receptor, the cell membrane invaginates (folds inward), forming a vesicle containing the LDL-receptor complex. This process is called endocytosis. The reference describes this as cells taking up LDL particles via receptor-mediated endocytosis.
-
Endocytic Pathway and Lysosomes: The vesicle containing the LDL particle is then transported along the endocytic pathway to cellular organelles called lysosomes.
-
Lysosomal Degradation: Lysosomes contain enzymes that break down the LDL particle, releasing the cholesterol into the cell.
| Step | Description |
|---|---|
| 1. LDL Binding | LDL particles in blood bind to LDL receptors on the cell surface. |
| 2. Endocytosis | Cell membrane engulfs LDL-receptor complex, forming a vesicle. |
| 3. Vesicle Transport | Vesicle travels along endocytic pathway to lysosomes. |
| 4. Lysosomal Release | Enzymes in lysosomes break down LDL, releasing cholesterol into the cell. |
In summary, cellular cholesterol uptake relies on the liver's LDL packaging and the receptor-mediated endocytosis pathway in other cells, ultimately delivering cholesterol to lysosomes for release and utilization within the cell.
