What is receptor mediated endocytosis? (1) How does it occur? (2) What are lysosomes? What are they good for, and how are they made? (1) Explain receptor recycling. (1) The sorting or proteins of different sorts into vesicles destined for different targets occurs in both the secretory and in the endocyto?c pathways. Where does sorting occur in each pathway. What are the similarities and the differences.(3)

 

 

As an introduction, The movement of macromolecules such as proteins or polysaccharides into or out of the cell is called bulk transport. There are two types of bulk transport, exocytosis and endocytosis, and both require the expenditure of energy (ATP).

Step-by-step explanation

1. Receptor-mediated endocytosis is a form of endocytosis in which receptor proteins on the cell surface are used to capture a specific target molecule.

• Clathrin-mediated endocytosis of many receptor types begins with the cargo ligands in the luminal compartment of the vesicle binding to receptors on the cell membrane.
• The cargo ligand and receptor will then recruit adaptor proteins and clathrin triskelions to the outside membrane of the cell around where budding will form.
• Budding of the plasma membrane then occurs, forming a clathrin-coated pit. Other receptors can nucleate a clathrin-coated pit allowing formation around the receptor.
• A mature pit will be cleaved from the plasma membrane through the use of membrane-binding and fission proteins such as dynamin (as well as other BAR domain proteins), forming a clathrin-coated vesicle that then uncoats and typically fuses to a sorting endosome.
• Once fused, the endocytosed cargo (receptor and/or ligand) can then be sorted to lysosomal, recycling, or other trafficking pathways.

2.A lysosome is a membrane-bound cell organelle that contains digestive enzymes. It is good for us because lysosomes are involved with various cell processes. They break down excess or worn-out cell parts. They may be used to destroy invading viruses and bacteria. If the cell is damaged beyond repair, lysosomes can help it to self-destruct in a process called programmed cell death, or apoptosis. Lysosome can be formed by budding off from the membrane of the trans-Golgi network. Macromolecules (i.e., food particles) are absorbed into the cell in vesicles formed by endocytosis. 

3. Receptor recycling involves two endosome populations, peripheral early endosomes and perinuclear recycling endosomes. In polarized epithelial cells, either or both populations must be able to sort apical from basolateral proteins, returning each to its appropriate plasma membrane domain.

4.Vesicles move proteins and lipids between organelles in the secretory pathway. Proteins are sorted in the Golgi and sent to the plasma membrane, lysosome or secretory vesicles. On the other hand, endocytic pathway occur in Endosomes are a collection of intracellular sorting organelles in eukaryotic cells. They are part of endocytic membrane transport pathway originating from the trans Golgi network. Endosomes represent a major sorting compartment of the endomembrane system in cells.

The main difference between secretory pathway and endocytic pathway is their mechanism first, secretory pathway is used to send proteins and lipids to the plasma membrane and certain membrane-bound organelles and to release material outside the cell. On the other side, cells not only release material to the external environment but they also take up material from outside the plasma membrane through endocytosis. There are several forms of endocytosis.

In a nutshell, secretory is all about sending and endocytic is about taking up. In terms of their similarities they are both significant process in our cells and they are vital in our bodies.

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