Bio 103 Lecture

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Bio 103 Lecture 10READINGSReceptor-media
ted endocytosis 17 727-735

• Vesicular Traffic II
• Endocytosis

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Vesicular Traffic II Endocytosis

• All eukaryotic cells undergo endocytosis
• -internalizing material from surroundings
• -types endocytosis
• phagocytosis
• pinocytosis
• receptor-mediated endocytosis
• EXAMPLE Low Density Lipoprotein (LDL)

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17-1 Overview of the secretory and endocytic
pathways of protein sorting
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Vesicular Traffic II Endocytosis

• All eukaryotic cells undergo endocytosis
• Endocytic pathway for LDL
• -cell-srface LDL-receptors bind LDL particle
• -clathrin coated pits containing receptor-LDL
  pinch off
• -coat shed
• -uncoated vesicle fuses with late endosome (low
  pH causes disassociation of LDL and receptor)
• -late endosome fuses with lysosome, LDL proteins
  and lipids broken down
• -LDL receptor recycles to cell surface

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17-27 Initial stages of receptor-mediated
endocytosis of LDL particles
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17-28 Endocytic pathway for internalizing LDL
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17-29 EM demonstrates that endocytosed
receptor-ligand complexes disassociate in the
late endosome
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17-30A Model for pH dependent binding of LDL
particles by the LDL receptor (cell surface)
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17-30B Model for pH dependent binding of LDL
particles by the LDL receptor (endosome)
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17-31 Delivery of PM proteins and cytoplasmic
components to the lysosome
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Vesicular Traffic II Endocytosis

• All eukaryotic cells undergo endocytosis
• Endocytic pathway for LDL
• HIV budding out from the plasma membrane employs
  same machinery as vesicle budding into endosomes
• -ESCRT complexes (endosomal sorting complexes
  required for transport) normally complete vesicle
  budding
• -viral proteins redirect ESCRT to plasma membrane
  to assist in viral budding

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17-32 Model for the common mechanism for
formation of multivesicular endosomes and budding
of HIV from the PM
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Vesicular Traffic II Endocytosis

• All eukaryotic cells undergo endocytosis
• Endocytic pathway for LDL
• HIV budding out from the plasma membrane employs
  same machinery as vesicle budding into endosomes
• Transcytosis moves some endocytosed ligands
  across an epithelial cell layer
• -EXAMPLE maternal antibodies in breast milk are
  absorbed by newborn mice via transcytosis

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17-34 Transcytosis of maternal milk IgG
immunoglobins across the intestinal epithelial
cells of newborn mice
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Vesicular Traffic II Endocytosis - SUMMARY

• All eukaryotic cells undergo endocytosis
• -internalizing material from surroundings
• -types
• phagocytosis
• pinocytosis
• receptor-mediated endocytosis
• EXAMPLE Low Density Lipoprotein (LDL)
• Endocytic pathway for LDL
• -cell-srface LDL-receptors bind LDL particle
• -clathrin coated pits containing receptor-LDL
  pinch off
• -coat shed
• -uncoated vesicle fuses with late endosome (low
  pH causes disassociation of LDL and receptor
• -late endosome fuses with lysosome, LDL proteins
  and lipids broken down
• -LDL receptor recycles to cell surface
• HIV budding out from the plasma membrane employs
  same machinery as vesicle budding into endosomes
• -ESCRT complexes (endosomal sorting complexes
  required for transport) normally complete vesicle
  budding
• -viral proteins redirect ESCRT to plasma membrane
  to assist in viral budding
• Transcytosis moves some endocytosed ligands
  across an epithelial cell layer
• -EXAMPLE maternal antibodies in breast milk are
  absorbed by newborn mice via transcytosis