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Endocytosis & Exocytosis . Pooja Patel Elizabeth Pemberton. Water and small molecules enter and exit cells through active transport and diffusion.
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Endocytosis & Exocytosis Pooja Patel Elizabeth Pemberton
Water and small molecules enter and exit cells through active transport and diffusion. • Large molecules, however, (proteins and polysaccharides) as well as larger particles are transported in and out of the cell after being packaged in vesicles. • Endo- and exo- cytosis require energy. Introduction
Cellsecretes biological molecules by the fusion of vesicles with the plasma membrane. • Steps: • Transport vesicles that buds off Golgi body moves along microtubules of the cytoskeleton to the plasma membrane. • Lipid molecules of from the vesicles and the plasma membrane rearrange, forming a fused membrane. • The contents spill outside of the cell. • The vesicle membrane becomes part of the plasma membrane. Exocytosis:
Examples: • Pancreas secretes insulin into extracellular fluid by exocytosis. • Neurons release neurotransmitters that signal other neurons or muscle cells. • Plant cells ( when making walls) deliver proteins and carbs from Golgi vesicles to outside of cell. Exocytosis:
Cell takes in biological molecules by forming new vesicles from plasma membrane. • 3 types: • Phagocytosis : (cell eats) • Pinocytosis : (cell drinks) • Receptor-Mediated Endocytosis (RME) Endocytosis:
Steps: • Small area of the plasma membrane sinks inward. • The pocket deepens and pinches into a vesicle containing materials from the outside of the cell. • Becomes a vacuole (for food or water) Endocytosis:
Enables cell to acquire bulk quantities of specific substances, even though those substances may not be in high concentration outside the cell. • Steps: • The ligands (molecule that binds to a specific receptor) attach to protein receptors that are on the outside of the cell. • A “fuzzy” layer of coat proteins are on the opposite side of the receptors on the inside of the cell. • Once the ligands bind to the receptors pocket forms and pinches into the cell. (The vesicle is coated by the “fuzzy” coat proteins. • Once the ligands are released, the receptor proteins are recycled back to the plasma membrane. RME:
Examples : • Cholesterols travel in blood in particles called low density lipoproteins (LDLs) • the LDLs act as ligands • When the LDLs are defective or missing, cholesterol builds up in blood vessels and can lead to arteriosclerosis. RME:
If pieces of the plasma membrane break off every time exocytosis occurs, how does the cell remain enclosed? Apparently, endo- and exo- cytosis offset each other. While one removes membrane, the other replenishes.
