PINOCYTOSIS VS RECEPTOR-MEDIATED ENDOCYTOSIS
Pinocytosis and receptor-mediated endocytosis along with phagocytosis are all forms of endocytosis which are classified under “active transport.” Active transport is a process in which particles or substances are being transferred from an area having a lower concentration to an area having a higher concentration on the contrary with the concentration gradient. Energy is needed to enable transportation of particles, and this energy is in the form of ATP or adenosine triphosphate. The whole process will eventually stop if in case there is no ATP available. Therefore, the cell function will be impaired and the organism might not survive. Pinocytosis and receptor-mediated endocytosis are both essential for cellular function to occur, thus making life possible. To make things clearer, we will distinguish some notable differences between receptor-mediated endocytosis and pinocytosis.
When cells do internalize specific particles or molecules, it is referred to as receptor-mediated endocytosis. The interaction depends totally on the so-called receptor found in the cell membrane which is a specific binding protein. These receptors found on the surface of the cell membrane attach only to specific components found in the extracellular space. To better understand this, let’s take iron as an example. Transferrin is a protein receptor responsible to transport iron into the blood. Iron molecules will be attached tightly to the transferrin receptor when these two meet up. After the process of binding, it will then be engulfed into the cell, and in the cytosol the iron will be released. Even if there is a few number of transferrin present, the cell will still be able to absorb the needed iron because there is a strong attraction between the transferrin receptors and its “ligand,” or the molecule, attached to the receptor. Ligand-receptor complex is the term used to describe the ligand fused to its specific receptor. This ligand-receptor complex forms a coated pit in a particular area of the membrane. This coated pit is very stable because it is also coated with clathrin. Clathrin also facilitates the transport process. The end form of this coated pit is called the “receptosome.” It is formed when the vesicle loses the clathrin coating. In contrast, pinocytosis is also known as “cell drinking” or ingestion of extracellular fluids (ECF). Much smaller vesicles are formed in pinocytosis compared to receptor-mediated endocytosis since it only ingests water plus minute substances rather than large particles that are solid. “Invagination” is the term use in pinocytosis to form a vacuole that is formed inside the cell. The typical transport mechanism that takes place in our liver cells, kidney cells, capillary cells, and those cells that line the epithelium is also pinocytosis.
In a much-detailed comparison, receptor-mediated endocytosis is very specific with regards to the materials it transports inside the cell because of the receptors present on the surface unlike pinocytosis which absorbs anything in the extracellular space. In terms of efficiency, receptor-mediated endocytosis wins over pinocytosis since it allows the entry of macromolecules which are needed by the cells for cellular function. Their mode of picking up molecules or particles on the extracellular space also varies. Pinocytosis has a much simpler way of absorbing substances over receptor-mediated endocytosis. Also, pinocytosis only absorbs water unlike receptor-mediated endocytosis which takes in large particles. Lastly, vacuoles are formed during the process of pinocytosis whereas in receptor-mediated endocytosis, endosomes are being developed.
SUMMARY:
1.Receptor-mediated endocytosis is very specific with regards to the materials it transports inside the cell unlike pinocytosis which absorbs anything in the extracellular space.
2.Receptor-mediated endocytosis is more efficient over pinocytosis.
3.Pinocytosis has a much simpler way of absorbing substances over receptor-mediated endocytosis.
4.Pinocytosis only absorbs water unlike receptor-mediated endocytosis which takes in large particles.
5.Vacuoles are formed during the process of pinocytosis whereas in receptor-mediated endocytosis endosomes are being developed.