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Biology 2382B Midterm: Session 6 Receptor-mediated Endocytosis

Course Code
BIOL 2382B
Sashko Damjanovski
Study Guide

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How can cells internalize the extracellular materials?
A cell needs to bring material into itself
Endocytic vesicles usually fuse with others to form the late endosome (pH change)
Eventually things will go to the lysosome.
Whatever was on the cell surface is now in the endocytic vesicles (early endosome)
Endocytosis:binging in things from the outside in
Encompass a large particle or another organisms
Only a few cells can undergo phagocytosis
Make small vesicles from plasmid membrane and often brings liquid into the cell
LDL (low-density lipoprotein)
Hormones (e.g. insulin), certain glycoproteins
Method of selective internalization of specific extracellular molecules (ligands)
Receptor Mediated Endocytosis
Low-density Lipoprotein (LDL)
Lipids are transported in large well-defined water-soluble complexes/particles called
Blood is hydrophilic
Single layer of polar heads on the outside and then the middle has cholesterol and other
non polar molecules
The structure is amphipathic, the outside is polar and the inside is non-polar
Composed of phospholipid monolayer, and apolioprotein
Water soluble, travel through the blood and go to various parts of the body
Cells that need fats and cholesterol will recognize these particles and bring them in via
The LDL is encompassed by apolipoprotein B.
Session 6: Receptor-mediated endocytosis
Thursday, February 4, 2016
11:44 PM
Midterm 2 Page 1

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Cells that need fats and cholesterol will recognize these particles and bring them in via
Going to help form a vesicle from the membrane
In the trans golgi and going to the late endosome you are using plasma membrane
Same thing here, you are using the plasma membrane to form an early endosome.
The receptors for these LDL particles are often associated with calthrin coated pits.
AP1 - TGN to the late endosome
AP2 - PM to the early endosome
Two layer coat: clathrin and adapter protein (AP) complexes:
Clathrin/Ap-coated vessicles
Other proteins can also have this motif
Coat proteins need to recognize a transmembrane protein because of a specific motif: NPXT
motif (amino acids)
Dynamen okays lots of roles in terms of where the membrane is brought together and is
used to separate different structures.
Dynamen will fuse together and will use GTP hydrolysis to basically separate the plasma
membrane from the vesicle.
Dynamen is a ring that constricts and as a result gets smaller and smalle and GTP
hydrolysis will release the vesicle.
Clathrin-coated cesicles pinch off using dynamic and GTP hydrolysis (dynamin forms rings
around the vesicle neck, polymerizes)
Recognized by AP 2 and start the formation of clathrin pit
Short C-terminal cytosolic segment with sorting signal (NPXY)
Recognizes the Apo Protein B
Long N-terminal exoplasmic segment with a ligand binding domain and b-propeller
This only happens at pH 7
At normal pH the ligand-binding arm binds tightly to ApoB
LDLR has three domains:
pH-dependent binding of LDL particles to the LDL receptor
Midterm 2 Page 2
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