Lecture 7- Types of Endocytosis

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Receptors, in a coated pit, bind to the molecule that will enter the cell. The pit is reinforced by a lattice like network of proteins called clathrin.

Additional clathrin molecules add to the lattice, which eventually pinches off part of the membrane and forms a coated vesicle.

Inside the cell, the vesicle soon becomes uncoated as the clathrin molecules dissociate from the vesicle and each other.

The vesicle then fuses with an endosome (another vesicle) from within the cell.

The receptors are released and recycled. The receptors are returned tot he plasma membrane to bind to further complementary molecules that need to undergo receptor mediated endocytosis.

The vesicle then fuses with a lysosome which carries enzymes capable of digesting the contents of the vesicle

Receptor Mediated Endocytosis

Phagocytosis

Chemotaxis and adherence of microbe to phagocyte

Ingestion of microbe by phagocyte

Formation of a phagosome (a vesicle forms around the microbe)

Fusion of the phagosome with a lysosome to form a phagolysosome

Digestion of the microbe by enzymes found in the lysosome

Formation of a residual body containing indigestible material

Discharge of waste material

Pinocytosis

Small droplets of extracellular fluid are taken in (no receptors are needed). All solutes in the extracellular fluid are taken in (non-selective)

Lysosomes break down the components into monomers such as amino acids

Occurs in most cells but especially in absorptive cells in the intestine and kidney

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