Transcript Receptor Mediated Endocytosis - UCO

Receptor-Mediated
Endocytosis
As Presented By
Michael Chan
Objectives
 Define
endocytosis
 Explain endosomes
 Illustrate receptor-mediated
endocytosis
 Give an example of receptormediated endocytosis
Endocytosis:
 Uptake
of extracellular materials
by invagination of the plasma
membrane to form a small
membrane-bounded vesicle
(endosome)
Endosomes
 Network
of tubules and vesicles
that receive materials taken up
by endocytosis
 Two types of endosomes
a. early endosomes
b. late endosomes
Receptor-Mediated Endocytosis
 Specific
receptors on the cell
surface bind tightly to the
extracellular macromolecule that
it recognizes (i.e. ligand)
 Plasma membrane region
containing the receptor-ligand
complex buds inward and
pinches off (i.e. transport vesicle)
Common Macromolecules that
Eukaryotic Cells Internalize by
RME :
 Choloresterol-containing
particles called LDL
 Iron-binding protein transferrin
 Protein hormones (e.g. insulin)
 Glycoproteins
Mechanisms of RME
 Clathrin-coated
pits
a. the invagination of the plasma
membrane is covered on its
cytoplasmic face by a layer of
bristly, electron-dense material
made of protein
b. form from trans Golgi
Mechanisms of RME (cont.)

Vesicles
a. spontaneous polymerization of
clathrin triskelions
b. lose coats after endocytosis
(early endosomes)
LDLs and Cholesterol
Metabolism
First studied and best understood
 Cholesterol is a hydrophobic
molecule that cannot be
transported in the blood in the free
state
 Carried as a giant complex, called
a low-density lipoprotein (LDL)

LDL Particle
 Surface
is a monolayer of
phospholipid and unesterified
cholesterol
 Hydrophobic core is rich in fatty
acid esters of cholesterol
 Hydrophobic apo-B protein is
embedded in the membrane
Questions?
Comments?