Exocytosis and endocytosis

Exocytosis• Types;• 1) Ca2+ triggered non-

constitutive (i.e., regulated exocytosis)  

2) non-Ca2+ triggered constitutive. 3) Vesicular exocytosis in prokaryote gram negative microbes is the latest finding in exocytosis.

Non-constitutive or regulated exocytosis

• Each specialized secretory cell produces large quantities of a particular prod-uct—such as a hormone, mucus, or digestive enzymes—which is stored in secretory vesicles for later release.

Vesicle Budding Is Driven by the Assembly of a Protein Coat

Vesicle Docking Depends on Tethers and SNAREs

Endocytosis• Types • Pinocytosis (“cellular drinking”)

• Phagocytosis (“cellular eating”)

• Receptor-mediated Endocytosis

Specialized Phagocytic Cells

• Function;

• nutrition

• defend us against infection by ingesting invading microor-ganisms.

• ingulf dead and dam-aged cells and cell debris.

Fluid and Macromolecules Are Taken Up by Pinocytosis

• macrophage, for example, swallows 25% of its own volume of fluid each hour. This means that it removes 3% of its plasma membrane each minute

Receptor-mediated Endocytosis

• receptor-mediated endocytosis, provides a selective concentrating mechanism that increases the efficiency of internalization of particular macromolecules

• such as; Cholesterol-containing LDLs, Vitamin B12 and iron

Endocytosed Macromolecules Are Sorted in Endosomes

• Early endosome–pH 6.5-6

• Late endosome–pH 5.5-5

Lysosome–pH 5-4.5

• transcytosis

Lysosomes Are the Principal Sites of Intracellular Digestion

• They contain about 40 types of hydrolytic enzymes

• ATP-driven H+ (proton) pump

• autophagy

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