Receptor-mediated endocytosis is one of the ways we get nutrients and materials into a cell.
The receptors on the outside of the cell act to keep out unwanted materials and take in things the cell needs. We will explore this specific type of endocytosis here.
What Is Endocytosis?
Endocytosis is a generalized term for whenever a cell takes in large molecules and other particulate matter available outside the cell. It does so in three different ways: phagocytosis, pinocytosis, and receptor-mediated endocytosis.
In all three forms, material to be ingested approaches the cell and begins to push the cellular membrane in. The membrane gives slightly, bending inwards. Once the maximum amount of material gets into the cell, the membrane will actually ‘pinch off,’ sealing the material inside of small organelles, called vesicles in animals and vacuoles in plants.
These vesicles and vacuoles will then meet up with a lysosome, organelles that contain enzymes, inside of the cell. The lysosome will utilize acidic enzymes to break down the material inside the vesicles and vacuoles, using that food as a source to create energy (ATP).
Receptor-mediated endocytosis differs from the other two forms of endocytosis in that it is very specific as to what it takes in. Think of it like someone who is a very picky eater, like a child.
They will only eat hotdogs and will refuse to eat anything else, so you have to make them hotdogs. How is it so specific? Well, inside of the cell membrane there are specific proteins that are exposed to the fluids outside of the cell, called the extracellular fluid. These proteins will only allow certain substances to attach to them. Think of it as a cellular lock and key.The specific substances that attach to these receptor proteins actually have a specific name, called ligands. In Latin, ‘ligare’ means ‘to bind,’ so these substances are literally binding substances. These receptor sites are located around the membrane of the cell in small clusters called coated pits.
How It Works
During receptor-mediated endocytosis, ligands are found out in the extracellular fluid. They will find and bind to proteins located in clusters in the cell membrane. These coated pits of proteins will collect the ligands and force the cell to bend inwards until it cannot take in any more ligands.Eventually the membrane will pinch off to form a vesicle trapping the ligands inside with the receptor proteins. A lysosome will attach to the vesicle, and using acidic enzymes, it will break down the ligands for use as energy elsewhere in the cell.
The receptor proteins that were in the vesicle are now liberated and free to move back into the cell membrane in order to collect more ligands. This allows the cell to take up bulk quantities of specific ligands that are otherwise only available in small amounts. In other words, it is like going shopping at a bulk store, like BJ’s or Sam’s Club.
You are able to get materials that you need in large quantities rather than singles.
One such example is cholesterol. Low-density lipoproteins, or LDL cholesterol, bind to LDL receptors in the plasma membrane. They then enter the cell through this receptor-mediated endocytosis. This is important because our bodies use cholesterol as a means of creating cell membranes and certain steroid hormones.
Endocytosis is a process by which substrates enter the cell via the plasma membrane.
The membrane bends in, allowing the substrates to enter, then pinches them in a vesicle that then breaks off. In receptor-mediated endocytosis, we see specific proteins in the membrane that only allow ligands, or binding substances, to bind with them. Thus, the cell is able to get a bulk material into the cell that it otherwise might not be able to get in such large quantities.