Transcript cell compartments #2 S07

Intracellular Compartments
and Transport
•Membrane Enclosed Organelles
•Protein Sorting
•Vesicular Transport
•Secretory Pathways
•Endocytic Pathways
•http://aimediaserver.com/studiodaily/videoplayer/?src=harvard/harvard.swf&width=640&height=520
Copyright © 2005 Pearson Prentice Hall, Inc.
Intracellular Compartments
and Transport:
Vesicular Transport
Function: carry soluble proteins & membrane
between compartments
Budding: driven by assembly of a protein coat
Docking: specificity depends on SNARES
Copyright © 2005 Pearson Prentice Hall, Inc.
VESICULAR TRANSPORT
• Vesicles bud off a compartment
• Transport between compartments
– Secretory Pathway: Golgi to plasma
membrane
– Endocytic Pathway: plasma membrane to
endosome to lysosome
Copyright © 2005 Pearson Prentice Hall, Inc.
Copyright © 2005 Pearson Prentice Hall, Inc.
VESICULAR TRANSPORT
1. Vesicles bud off a compartment
2. Transport between compartments
Endocytic Pathway: plasma membrane to endosome to lysosome
Secretory Pathway: Golgi to plasma membrane
Copyright © 2005 Pearson Prentice Hall, Inc.
Vesicle Budding
• Protein coat assembly
– on cytosolic surface
– COP- coated
• ER to Golgi
• Within Golgi
– Clathrin coated
•
•
•
•
Clathrin coated pit
Dynamin protein : constriction, binds GTP
Adaptin proteins: anchor clathrin, cargo receptors
Cargo receptor : bind transport signals
Copyright © 2005 Pearson Prentice Hall, Inc.
Clathrin:
Clathrin Coated Pit =>
Clatherin Coated Vesicle
Copyright © 2005 Pearson Prentice Hall, Inc.
Vesicle Budding:
Clathrin
Clathrin coated pit
Dynamin protein : constriction, binds GTP
Adaptin proteins: anchor clathrin, cargo
receptors
Cargo receptor : bind transport signals
Copyright © 2005 Pearson Prentice Hall, Inc.
Vesicle Docking
• Organelle Recognition
• v-SNARE
• t-SNARE
• Membrane Fusion
– Water removed: enzyme complex
– Intertwining of SNAREs
Copyright © 2005 Pearson Prentice Hall, Inc.
Copyright © 2005 Pearson Prentice Hall, Inc.
Endocytic Pathways
1. Phagocytosis: Specialized Phagocytic Cells
Ingest Large Particles
2. Pinocytosis: Take up Fluids and
Macomolecdules
3. Receptor Mediated Endocytosis: Forms
A Specific Route into Animal Cells
4. Endsomes: Sorting Endocytosed
Macromolecules
5. Lysosomes: Principal Site of Intracellular
Digestion
Copyright © 2005 Pearson Prentice Hall, Inc.
Endocytic Pathway:
Phagocytosis, Pinocytosis
• Phagocytosis : phagocytic cells
(macrophages)
– Bacteria, dead or damaged cells, deris
– Pseudopods form phagosome
– Phagosomes fuse with lysosomes
• YB bacteria : interfere with fusion
– Recognition molecules : phagocytic
receptors
• Opsonised bacteria
Copyright © 2005 Pearson Prentice Hall, Inc.
Copyright © 2005 Pearson Prentice Hall, Inc.
Endocytic Pathway:
• Pinocytosis
– Fluid and small particles
– By clathrin –coated pits
– Fluid intake balanced by fluid exocytosis
Copyright © 2005 Pearson Prentice Hall, Inc.
Receptor Mediated Endocytosis:
Cholesterol Uptake
• Cholesterol transported as LDL
• Endocytosed via receptors for LDL
• LDL-receptor complex dissociated in
endosomes
– Receptor recycled to membrane
– LDL to lysosome
• Protein –cholesterol dissociated
• Cholesterol released to cytosol
• Genetic condition: defective LDL receptor
Copyright © 2005 Pearson Prentice Hall, Inc.
Receptor Mediated Endocytosis:
Cholesterol Uptake
Copyright © 2005 Pearson Prentice Hall, Inc.
Fate of Receptors in Endosomes
Recycled
Degraded
Transcytosed
Copyright © 2005 Pearson Prentice Hall, Inc.
•
•
•
•
Lysosomes
Sacs of hydrolytic enzymes
pH ~ 5 : optimal activity of enzymes
Enzymes: tagged with mannose-6-P in ER
Unique membrane
– ATP proton pump
– Transport proteins
– Membrane proteins
glycosylated
Copyright © 2005 Pearson Prentice Hall, Inc.
Protein Glycosylation
Copyright © 2005 Pearson Prentice Hall, Inc.
Secretory Pathways
Covalent Modification in ER
ER Exit Controlled to Ensure Protein
Quality
Further Modification & Sorting in Golgi
Released from Cell by Exocytosis
Copyright © 2005 Pearson Prentice Hall, Inc.
Secretory Pathways
Constitutive
Regulated
Copyright © 2005 Pearson Prentice Hall, Inc.