Molecules can cross membrane in a number of different process that either use their own energy or rely on an outside energy source. Endocytosis is the one of the process that transfer material across the membrane.
Endocytosis is the movement of bulk material including proteins, fluids, electrolytes, microorganisms, and some macromolecules across the plasma membrane. The word endocytosis is derived from the Greek word endonmeans within. It was first described by Christian de Duve in 1963. Endocytosis is a energy requiring process as adenosine triphosphate.
In mammalian cells endocytosis is regulated by the alternation in the function and composition of the plasma membrane and is mediated by clathrin
The Basic Steps of Endocytosis
Three main steps are involved in the process of endocytosis are following
- First the plasma membrane is fold inward to form a cavity that fills with extracellular fluid, dissolved molecules, food particles, foreign matter, pathogens, or other substances.
- Then the plasma membrane folds back on itself until the ends of the in-folded membrane meet and form a vesicle to trap the fluid inside the vesicle.
- The vesicle is pinched off from the membrane to the cytoplasm inside the cell.
Function of Endocytosis
Basically, it regulates diverse process in the cell use for
- Homeostasis of cell
- Signal transduction
- Receptor signaling
- Entry of pathogen
Types of endocytosis:
The three forms of endocytosis is
- Receptor mediated endocytosis
Pinocytosis is called cell drinking derived from the Greek word pinein mean to eat and cyto mean cell. It is the nonspecific uptake of small particles suspended in extracellular fluid. It was discoved by Warren. H lewis in 1931. The particles move across the membrane through pinocytosis are tiny in size that are required for the survival of the cell such as sugar, amino acids, enzymes, hormones etc. kidney cells take in fluid to maintain fluid balance through pinocytosis.
Phagocytosis is similar to pinocytosis but it is a specific type of endocytosis by which cell takes solid material rather than liquid. Phagocytosis is different from the pinocytosis in many aspects.
Large particles move across the membrane via phagocytosis such as bacteria, viruses etc. For example, white blood cells engulf and digest bacteria through phagocytosis. Thus, help in the immunity process in the body.
Difference between pinocytosis and phagocytosis:
Summary of difference between phagocytosis and pinocytosis is following
|Uptake of solid material||Uptake of fluid particles|
|Formation of phagosomes||Formation of pinosomes|
|Require lysosome||No role of lysosome|
|Help in cell survival||Help in defense purposes|
Receptor mediated endocytosis:
Receptor mediated endocytosis also called clathrin mediated endocytosis is the process in which specific receptor protein recognizes and binds with the extracellular molecules and then imported into the cell. A variety of molecules such as cholesterol move across the membrane through receptor mediated endocytosis. Example of receptor mediated endocytosis is uptake of large molecules by the intestinal cells from the inside of gut.
Similarities between pinocytosis and phagocytosis:
- Both are the active process
- Both requires energy (ATP) as adenosine triphosphate for the uptake of materials.
- Vesicles formation