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BIO230H1 Study Guide - Final Guide: Golgi Apparatus, Synaptic Vesicle, Tight Junction

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Kenneth Yip
Study Guide

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Lectures 1-3: Organizing the Cell and its Outside Interactions
We're asking: How do cells and tissues organize themselves spatially?
1. Membrane Trafficking
Required for:
cell-cell communication
Resource acquisition
NB: Requires dynamic changes to the plasma membrane
Basic Principles of the Biosynthetic-secratory and endocytic pathways:
1. The presence of polarized trafficking routes (travel from a place to another
in the cell)
2. Sorting Station (similar to bus stations)
- Sites of arrival events from many places with many materials
- Multiple different departure events
- Early endosomes: Multiple outputs (in from the plasma membrane, out to the lysosome, Golgi
and ER)
How does a cell know where to go
i.e Cisternae of the golgi (trans golgi network), secratory vesicles, and early
endosomes (but not lysosomes)
3. Retrieval mechanisms are needed so there is a general balance between all of these routes
- Material is sent from ER to Golgi but some need to be sent back (if not will deplete cells of
Ex. From ER to Cis Golgi network and endosomes comming into the cell from
external env.
Secratory pathways (out of cell) = Two types
I. Consitutive Secratory Pathway: Continuous flow of material outside of the cell (no regulation at all). Will
dock and fuse with plasma membrane
II. Regulated Secratory Pathway: Starts in the same way, but changes. A vesicle buds off but
waits for a signal (hormone or neurotransmitter or maybe even a ligand) until its told to
bud with the plasma membrane and exit the cell. Alll vesicles are stored until a signal
triggers docking and fusing of all (i.e. Allergies and histamine release). Provides extra
plasma membreane when needed (i.e in the cases of Cleavafe furrow, phagocytosis, and
wound repair).
Regulated secretion in terms of extracellular signals
1. Delivery of synaptic vesicle to component of plasma membrane
2. Endocytosis of synaptic vesicle compoments to form new synaptic vesicle directly
3. Endocytosis of synaptic vesicle components and delivery to endosome
4. Budding of synaptic vesicle from endosome
5. Loading of neurotransmitter into synaptic vesicle
6. Secretion of neurotransmitter by exocytosis in response to an action potential
In both Pathways, the concentration of the secretory vesicle is due to the fact that after it buds, parts of
the membrane with the clathrin coats break off and go back to the trans Golgi network thus
concentrating the content of the vesicle
Endocytic pathways counterbalance secretory pathways and perform specific functions
Steps to endocytosis: Invagination and Fission
It Starts at early endosome
- Endosome has choices to make on where contents go
Can either be destroyed by lysosome, can be recycled back into the basolateral domain of
plasma membrane or leave through another part of the plasma membrane through

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Cells collect resources by endocytosis (ex. Cholesterol)
- Bringing things into the cell
- Needs cholesterol from fluids outside of cell
- This cholesterol is brought in by the Low Desnsity Lipoprotein receptors (binds to cholesterol - cell
has receptors that are TM proteins and recognize and grab LDL and drags it into an endocytic pit
and is brought into the cell through endocytosis.
- Now, coated vesicle, then targeted to go to sorting station.
- Receptor is recycled (sent back to the membrane to be used again)
- LDL is targeted to the lysosome, once targeted there, the lysosome (low pH and digestive effects)
then release LDL as free cholesterol into the cell, used to build membranes
Want receptor to go to the membrane and not lysosome
So LDL comes in and goes to the lysosome
Cells down regulate cell surface signalling by endocytosis
- Phagocytosis
- Can control signaling with endocytosis
- If it wants so shut signaling complex down it can just completely remove the signaling complex
- When that happens, there are signal on outside of the cell, the membrane, receptors and and
adaptor molecules and such on the inside of the protein. This way you can pull the whole complex
into the cell
- After endocytosis through specific sorting can be converted into a multivesicular body by pulling
the whole membrane into the lumen of a larger vesicle (vesicles inside of vesicles)
This membrane composes the entire signaling complex, and can be sent to lysosome and
fuses with it and shuts down the signaling complex
Know how budding and invagination occur
Also be careful of the wording BUDDING AWAY FROM CYTOSOL = ENDOCYTOSIS
Formation of Lysosome: Early endosome + ubiquitin --> Pinches off to form a multivesicular body -->
Lysosomal lipases from late endosome/lysosome binds and releases contents making multivesicular
body a lysosome
1 v-SNARES (vesicles) and 3 t-SNARE (target membrane), proteins that pull two membranes
together by coming closer and squeezing water out.
Clathrin Drives vesicle invagination:
Cargo receptor in membrane attaches to aptor proteins, this complex binds to cargo and pulls
into the structure, clathrin then binds atop all of that and helps bud the vesicle.
Clathrin triskelion is composd of 3 heavy chains and 3 light chains; form a cage-like structure
COPI and COPII drive invagination
Made of: selected membrane proteins, Sec23/24, Sar13/31 and Sar1-GTP
Sec23/24 binds to the selected membrane proteins, next to sec23/24, Sar1-GTP is bound the
membrane. Sec13/31 binds to Sar1-GTP which then composes the outer coat.
Dynamin drives fission after vesicle invagination (helps exclude water so membrane can bind with
ESCRT Complex
Using clathrin to pull out of the cytosol by use of protein complexes and PI(3)P and PI(3,5)P2
Viruses typically can use this
Proteins Coating per section of network
COPII only used in Cis Golgi Network (so from ER TO CGN)

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COPI for return from CGN to ER or to directly transport stuff out of cytosol from TGN
Clathrin is for the TGN and and signals that vesicle go to an early endosome
Be sure to understand the above content
Phosphatidylinostiol (PI, with phophorylative modification it becomes PIP) can have modification at
different positions of the inostiol -OH head group
PIPs bind very specific proteins which then ensure specificity (ex. Different PIPs are used at different
stages to control trafficking networks
What posititions Phosphatases and Kianases that position the PIP
Must know what GEFs do (they promoate exchange of GDP to GTP) and GAPs (GTP->GDP)
Specific Rab small GTPases localize to distinct sites in the trafficking pathway
Rab11 = recycling endosome
Rab5A = Plasma membrane, clathrin-coated vesicles, early endosomes
Rab 7 = late endosomes
- Rab5, its GEF exchanges GDP for GTP, gives it a lipid anchor (in inactive state tucked into the
protein - due to conformational change) localizes it to target membrane
- One of these downstream regulated molecules itself can be Rab-GEF which results in positive
feedback loop
Can interact with PIPs and attract other proteins to the chain etc.
Also, specific Rab with a specific PIP will is a control mechanism
Rab-GTP on vesicle (with v-SNARE also on vesicle) binds a Rab effector which is called tethering,
and then it allows for the fusion of the vesicle and release of contents. This all works together in a
combinatorial effect (specific rabs to SNARES)
Organization of cell is based on the organization of the trafficking networks that run throughout the cell
Lecture 2 Notes: Cortical Polarity, the Cytoskeleton and Cell Migration
The cytoskeleton is polarized (from the subunits to the protofilaments to the network even)
Each protofilament is made of heterodimers of the monomeric proteins a-Tubulin and B-
Tubulin (tubulin monomers bind and hydrolyze GTP).
The heterodimers are asymmetric (thus, assembly head-to-tail results in polarized tubules)
y-Tubulin binds tubulin heterodimers assembling these protofilaments into tubes
The latter also nucleates microtubules at the (-) end
The (+) end grows away from the centriole (for example)
The Microfilaments are made up of a y-tubulin ring (makes a positively charged ring) which
allows the a-B-tubulin heterodimers to associate via the (-) end allowing the (+) end to grow
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