BIO241 Lecture 13-14

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2 Feb 2013
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Tuesday, February 24, 2009
- Degenerative diseases & infectious diseases as well.
- Beginning this week, we’re going to be talking about cytoskeletal
machinery inside cells.
- Next week, we’ll talk about cell junctions, how cells stick to each other.
- Then the extracellular matrix that surrounds cells, how cells stick to this
matrix & interact with that matrix.
- Then switch gears to talk about the control of cell numbers, looking at
the cell cycle & programmed cell death.
- Looking at mitosis & cell division & how the control of cell numbers is
associated with cancer.
- Finally we’ll touch on how multicellular organisms develop in the last 2
lectures.
- The assigned readings are focused on the topics he covers in lectures.
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- Here we have 3 cells that have very different shapes to them. These
different shapes are linked to the different functions of cells.
- The Goblet cell has a structure to it that’s focused on pumping mucus
into the lining of our throat and so on. Here’s the nucleus of this cell in
the diagram & basically the rest of the cell is filled with these vesicles
that are involved in pumping out this mucus into the extracellular space.
- Compare that to a sperm cell in the middle diagram – this sperm cell has
a structure that is made for motility, made for swimming. The nucleus is
at the top & then you have this huge tail at the end further down.
- Photoreceptor cell has the nucleus in the middle. On the top are the
specific membranes that pick up the photons of light so these are in our
eyes & then this light info is then passed through the cell to a synaptic
region which then connects to neurons so that we can connect what we
see to neurons that link to our brain.
- So each of these 3 cell structures is closely linked to its function & the
cytoskeleton plays an essential role in making these 3 structures & all cell
structures.
- Here is an example of microtubules in green, reaching out & grabbing
onto chromosomes in blue & then they’ll pull these chromosomes, half of
them onto one side & the other half on the other side to divide the genetic
material into 2 cells.
- An example of cell-cell interactions here is a field of cells. Inside one
of the cells in green are intermediate filaments, these are cytoskeletal
filaments & they basically have this network of filaments that are filling
up this cell. Again you can see the nucleus & filling the cytoplasm we
have these intermediate filaments reaching out & in blue are cell adhesion
complexes that link one cell to its neighbouring cell. We can see that as
these intermediate filaments reach up to another cell complex, there is
another set of intermediate filaments in the neighbouring cell that reach
out & connect to this one & they’re connect via this cell-cell adhesion
complex.
- Basically what this makes is a tissue-wide protein interaction network
so you have this network of intermediate filaments in one cell connected
to the network in the neighbouring cell through these cell adhesion
complexes & by having this network running through this whole tissue, it
gives the tissue a lot of strength.
- This is what the cells in your skin would look like & it gives them a lot
to strength to withstand physical stress.
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- Cytoskeletal networks provide structural frameworks for cells & cellular
processes.
- We can compare this sort of structural framework to other structural
framework such as the scaffolding of building like the BCE place. We
can think of skeletons in our own body.
- In most cells, the cytoskeletal is actually constantly turning over it’s
being broken down, rebuilt, broken down & rebuilt. This allows the cell
to regulate that cytoskeleton to create new configurations of the
cytoskeleton to create new cell shapes or to regulate a new cellular
function.
- This ability to remodel this really dynamic scaffold of the cell is really
quite remarkable.
1) Intracellular traffic
2) Chromosome separation during mitosis
- This can be associated with intracellular traffic, for example. For this
cell, you can see the nucleus. Just outside of it in green are the vesicles of
the Golgi apparatus & in red, we have microtubules that would be
involved in transporting these Golgi vesicles to another part of the cell.
- Chromosomes can be separated in mitosis by microtubules pulling them
apart.
- We’ll see in future lectures how cables can function in cytokinesis or
cell division & for providing mechanical strength to tissues.
- Here you can imagine an analogy being to a ski lift where we have the
cables of the cytoskeleton transporting these cars up the mountain so
these cars here could be the Golgi vesicles that are moving along the
microtubules.
- These analogies break down when it comes to the dynamics of the
cytoskeleton inside cells. So this is very dynamic, constantly forming &
breaking down whereas in this case, the ski lift is stably in place.
Filopodia + lamellipodia for cell migration
Stereocilla in sensory cells
- So these protrusions include filopodia & lamellapodia for cell
migration, also stereocilla in sensory cells & microvilla.
- Here’s an example of a protrusion this is microvilla coming out of a
gut cell so we have this very long protrusion out of the plasma membrane
so the black line is the plasma membrane & the cytoskeletal structure
inside of this is acting like a pole to poke this microvilla out of the top of
the cell. So in this case, it’s increasing the ability of gut cells to absorb
materials by increasing the surface area of the gut.
- The analogy here, we can imagine here that we’ve got this plasma
membrane being distorted by this pole & that’s like the covering of this
tent being distorted by the pole inside.
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