Answer to Question #111763 in Cell Biology for MAKHUOGA ALFRED FRIDAY

Question

3. Finally, explain the difference between endocytosis and exocytosis and provide an example of a molecule (remembering to state its function) that is transferred using this method.

Answer 1

First of all, endocytosis and exocytosis are the types of active transport, so they require an energy of ATP to occur in a cell.The main difference is in the directions of delivery of substances. Endocytosis is the general term for processes of vesicular transport in which substances enter the cell. It plays key roles in nutrient uptake,cell signaling, and cell shape changes. Exocytosis is the general term for processes of vesicular transport in which substances leave the cell.

Some of the endocytotic processes require special proteins during vesicle formation. The best known protein is clathrin. The presence of clathrin is certainly important for endocytic vesicle formation, many vesicles are formed in a clathrin-independent manner using other proteins ( caveolins or flotillins). There are three mechanisms of endocytosis in the cell:

-Pinocytosis

-Phagocytosis

-Receptor-mediated endocytosis

Exocytosis is the process by which a vesicle moves from the cytoplasm to the plasma membrane, where it discharges its contents to the extracellular space. Presence of specific proteins on their surface (coatomers) mediate the movements of these vesicles. There are two mechanism of exocytosis:

-the constitutive

-the regulated secretory

Examples:

-acetylcholine is secreted by exocytosis into the synaptic cleft. Acetylcholine is a neurotransmitter, which provides muscle contractions.

-cholesterol travels in the blood in particles called low-density lipoproteins (LDLs), each LDLs bind to LDL receptors on plasma membranes and then enter the cells by endocytosis.Cholesterol is used for membrane synthesis and the synthesis of other steroids.