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Lecture notes of 9 pages for the course Membrane and cellular Biochemistry at QMUL
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Endocytosis and exocytosisLearning objective:
1. Explain an experiment using green fluorescent protein (GFP) that showed protein movement between the different
compartments (organelles) of the endomembrane system
2. Describe the basic features of vesicle transport
3. Differentiate between the roles of vesicle transport in secretory pathways and the endocytic pathway
4. Distinguish between the different types of protein-coated vesicles and their specific roles in vesicle transport
5. Explain the proposed mechanism of assembly of the COPll (coat protein 2) coat
Cellular organelles and membrane trafficking
Membranes are dynamic
Membranes communicate
Membrane invagination (endocytosis) forms a route into the cell
Membrane fusion with the plasma membrane (exocytosis) forms a route out of the cell
The plasma membrane is shaped by the cytoskeleton
Membrane-bound compartments can be visualised by electron microscopy (EM)
Function of ER:
- RER synthesises (membrane + secretion) proteins
- ER: simple modification of protein (i.e. glycosylation), folding
Membrane-bound compartments can now be visualised with fluorescently tagged proteins
GFP-Labelling of endoplasmic reticulum in a mouse fibroblast
Time-lapse
- Shows that ER is dynamic (constantly moving)
LO2. DESCIBE THE BASIC FEATURES OF VESICLE TRANSPORT
LO3. DIFFERENTIATE BETWEEN ROLES OF VESICLE TRANSPORT IN SECRETORY PATHWAYS & ENDOCYTIC PATHWAYS
Biosynthetic (secretory) and endocytic pathways
1. Constitutive secretory pathway:
- Material transported in a continual manner
2. Regulated secretory pathway:
- Material (digestive enzymes, hormones, neurotransmitters) are stored in membrane-bound packages.
- Released into extracellular space in response to stimulus
3. Image shows:
- Protein synthesis in the ER
- Vesicles (carry cargo) bud off specific areas of ER membrane
- Cargo moves from the ER to Golgi
- Fusion of vesicles with the Golgi
- The processing events happen as the Golgi occurs
- The cis (same) side of the Golgi faces the ER
, - Material travel from the cis to trans side of the Golgi complex.
- Vesicle formation again at the trans side of the golgi complex
- Vesicles can do many things
i.e. secreted depending on the type of cell
- there are 2 pathways of secretion
1. constitutive secretory pathway (material continually being secreted outside the cell into the ECM)
i.e. ECM components
plasma membrane
2. Regulated secretory pathway
Vesicles bud off the Golgi
Move to the plasma membrane
Can build up large concentrations of big granulated dense vesicles close to the membrane but not
released
Something triggers the fusion of the regulated vesicles with the plasma membrane
o i.e. if neurotransmitter is in the vesicle then the electrical impulse will trigger the release of the
neutotransmitter
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