Lec 1 - Prof Harris.
October 25, 20138:21 PM
2 linear polypeptides are coming together to fomr a dimer non
Important question and is relevant to disease. Because when cells
that paly a normal role in the body are the ones which goes
berserk when we get diesases
BIO230 Page 1 BIO230 Page 2 BIO230 Page 3 --> PM surrounds the other surface of the cell. Interface between the
internal and external environment.
Nice example: epithelial cell connected to another epithelial cell.
These cells coats our gut. There are specific ends in the which faces
the lumen of the gut which allows the cell to collect nutrients (pink).
There are different molecular properties on the other side of the cell.
Neurons: have two diff. main regions. Allows the neuron to collect
signals from the dendrites and send it to the brain. To send neuro
signal throughout the body
How is the PM organization controlled? This is through membrane
Inside: white is cytosol
Grey particles are membrane bound compartments.
Small ones are vesicles
The big one is the Golgi apparatus é ER
The black lines are also membranes and inside these membrane
there is a separate aqueous environment.
So there are different pathways to bring in and out membrane
material to and from the PM.
Endocytic pathway: what comes in
Biosynthetic secretory pathway: brings out
ER : proteins are been made. They can be transported to the PM
Extracellular and then taken to the lysosomes. Where proteins are been broken
down. There are several basic principles to the trafficking routes.:
space these regoins that are been marked has the potential of There's a
flux of proteins from where proteins are to be made , used and
broken down. There are trafficking system which are clearly
defines. Polarized trafficking routes because all lines of the
material is directed in one way.
There arent simply single one way routes. There are also sorting
BIO230 Page 4 Protein trafficking routes
Membrane compaortments are coming from different sites and
joining one site. This one site sends out materials to different end
points. Things are coming from one place and goes to a different
place of the cell.
BIO230 Page 5 Retrieval Mechanisms and Genral Balance Among Routes
The cargfo needs to be maintained in the overall cell. Endocytosis
have to match exocytosis or else the cell is going to shrink or grow in
size. The golgi has a place to take things and receive things.
Constitutive: the cell is basically pumping things out from the cell
continuously. It makig things from the ER to the golgi, making new
secreted materials (blue) membrane lipids, proteins and these are
constantly taking things to the membrane to resupply. The other
materials are breaking down and these are resupplying them.
Regulated secretion: the cell will make a store of vesicles containing
specific cargo. Its only want to send it in a specific situation: eg:
sending nerve impluses. Immune response.
These vesicles are waiting for the signal and the signal comes along
and activates the signal.
BIO230 Page 6 Regardless of constitute or regulatory the mechainsm of going
thorugh is kind of similar:
The mechanism of these pathways:
Cargo concetration and Retrieval of the transport machinery back
into the system.
In the golgi the cargo is not that concentrated --> it buds off to a
immature secretory vesicle --> it has golgi components attached to
it --> and recycles the golgi materials back to the golgi so the golgi
maintains its size --> it becomes a mature secretory vesicle that
can be secreted and released in the contrated forms of cargo. And
releases the cargo.
Concetrated cargo maintains the balance of the system
A cargo just about when its about to be secreted from the surface
of the cell. Conc cargo is the black blob.
Lumen of the cargo. And the extracellular space.
Seperating the two aquesous environements are membranes. The
dark lines the outer plasma membrane. The vesicle will dock with
the PM --> but there is a membrane as a barrier --> the
membranes will fuse --> and recoil back and now
Cargo cannot leave the cargo can be released to the extracellular space
membrane is blocking
BIO230 Page 7 Mast cell: functions in immune response. When there is a pathogen I
the system it releases histamin so it can attach the prey.
Unstimulated state: vesicles are packed with histamin. Upon extra
cellilar stimulatn formed in repsonse to the pathogen the vesicles
fuses with the PM and release the histamin into the environement.
Changes the environemetn and allowes other cells to come in and
attack the prey easily
Exocytosis can fill the membrane
Which the bacteria A: Cell division. This is a Cell at a late stage of division. A single cell
becomes two daughter cells and There is a huge need for a new PM in
Fills up between the cells.
B: immune cells takes the bacterium as phagocytosis. It takes a huge
part of the PM with it. So exocytosis can resupply the PM
C: Wound: physical lose of PM. So it is replaced by exocytosis.
BIO230 Page 8 Endocytosis. Endocytic apthways conuter balance the secretory
pathways. Perfomrs specific functions as well
The PM starts to bend in and eventually the two lipid bilayers fuse
and the vesicle pinches off into the cytosol.
Once the vesicle has been endocytosed into the PM it has some
choices to make.
BIO230 Page 9 The endocytosis vesicle comes in
Can go to the early endosomes which is a sorting station, and from
there it can go to lysosome to be degraded, or to be recycled. Or to
trasncytosis to another part of the cell.
Example of where cells use endocytosis: to collect cholesterol in the
LDL - low density lipo proteins are floating around in the blood.--> LDL
receptors bind to LDL--> recruit them to the sites with membranes
bends in and pulls in the PM> puls the LDL with it--> its
endocytosed- -> and sent to early endosomes to sort.
LDL is released from the receptors and its receptors are used to send
LDL and at this point it is released and it gets sent to lysosome. The
lysosome degrades all the protein and releases choelsterol so it dan
be released into the cell.
BIO230 Page 10 The immune cell can pull the bacterium into the cell.
And what is the machinery that is used?
BIO230 Page 11 Fusion Exocytosis: appears as a fusion.
Look at the PM> the contents at the vesicle to be transported the first
two membranes has to fuse.
The grey material is the cytosol. There is three aquesou membranes
other than the cytosol
. Lumen of the vesicle
Critical think to keep track of: what happens to the lumen of the
vesicle in contrast to the cytosol. The lumen of the vesicle becomes
continuous with the extracellular space
During exocytosis the lumens are readying itself to the become the
Endocytosis: what was the extracelular space is now in the
lumen. It is in the opposite membrane configuration, and the
invagination mmebrane is bending and the membrnae is invagination into
the large cytosolic space.
BIO230 Page 12 Little hard to understand: Budding of cytosolic particles into the
Good way for cells to destroy contents lumen of the vesicel. It happens in the late endosomes to go
onto the lysosomes.
In the late endosomes there are membrane bound
compartments inside the endosome and they are white colored
so they were derived from the cytosol. Membrane bound
compartments inside the endosome. Big chunks of the cytosol
are picked upand drawn into the endosome so they can be
destroyed in lysosome.
Multivesiclualr body: b