Facilitated Diffustion - Transport in Plants, Biology, Class 11 Video Lecture

in the first video on passive transport
we talked about the most passive of
passive transports and that is simple
diffusion and we talked about how small
non charged non-polar molecules would
actually have the easiest time things
like carbon dioxide or molecular oxygen
would have the easiest time diffusing
through the cellular membrane they are
small enough to kind of get through the
little gaps here and then since they
have no charge or polarity they're going
to they're going to be fairly
indifferent as they pass through and we
talked about in between you have things
like water molecules which are small
enough to pass through the gaps but they
have some polarity so they're not going
to be able to get through super easily
but they will be able to seep through
and then we talked about things that
would have a tough time and that's
charged particles because charged
particles that we have some ions right
over here sodium ion a potassium ion
even though these are fairly small
they're going to interact a lot with the
phospho with the phosphate heads right
over here with this charge which is
going to keep which is going to make it
hard for them to actually penetrate
through the membrane what I want to talk
about in this video is still passive
transport remember passive transport is
about not using energy it's about moving
down the concentration gradient but
we're going to talk about ways that
passive transport can happen a little
bit easier for some of these molecules
over here and that's because their
transport their passive transport is
going to be facilitated so what we're
going to talk about in this video let me
figure out a place where I can write it
is facilitated facilitated diffusion let
me write that down
facilitated facilitated diffusion so the
last video was just straight up
diffusion now we're going to talk about
facilitating it so what do you think if
you were trying to engineer something
that would make it easy for these things
these these types of molecules either
water molecule or anion to move down its
concentration gradient what would you do
well the you might say well if I did if
you didn't have to mess with all of this
you know all the the hydrophilic heads
and then the hydrophobic tails and then
the hydrophilic heads here well that
would make it pretty easy to move down
your diffusion gradient and that's
exactly what has emerged in nature
essentially just tunnels through tunnels
through the
membrane and so one form of facilitated
diffusion can happen through what we
call channel proteins let me write this
in orange for no good reason
channel channel channel proteins channel
proteins and an example of a channel
protein might be this one right over
here and maybe this one is specialized
for being a channel for water for and so
we would call this this particular one
we could call an aquaporin aqua
aquaporin which is just a channel
protein for water and so you see it has
this hole on top and let's say you had
more water molecules outside the cell
then you have inside the cell and you
wanted to move down its concentration
gradient or maybe just what you have a
higher concentration of solute here and
so we're going to have osmosis occurring
so the water molecules are going to
they're more likely to come they're more
likely to come from the outside to the
inside then from the inside to the
outside and so you could have water
molecules going there they don't even
have to really mess with the membrane
they're just going to go through this
aqua port pro this aquaporin and then
come out come out on the inside of the
cell and you have similar channel
proteins for ions so this might be one
for ions and so let's say this is a
sodium these are sodium ions right over
here they're charged they would have
trouble getting through but this channel
protein might be might be specific to
them and allows them it allows them to
go through and as we'll see when you
study things like neurons will see that
these channel proteins especially for
ions are incredibly important for
amplifying an electrical signal down or
a chem Oh electrical signal I guess I
could say and they can also be gated
they can also open and close depending
on two different conditions that are in
different parts of the cell so these
channel proteins they could just be open
or they could be open and closed gated
based on different conditions which you
can see that's actually key to what
happens in nerve cells that we'll see in
future videos now another type of
facilitated diffusion can occur through
what we call carrier proteins carrier
proteins
and I want to be clear well I'm going to
talk about carrier proteins but people
are still studying exactly how they work
but the view is okay let me just draw
the membrane here let me draw let me
draw a membrane I'm going to do a
carrier protein I'm going to draw a
carrier protein in the membrane so this
is a this is a cross-section of this is
of my membrane my phospholipid bilayer
here almost done and then a carrier
protein the way I'm going to draw it
isn't exactly how a carrier protein
would actually look but it would
hopefully give you the right idea so
maybe it's like this maybe it's like
this and things if things want to move
down their concentration gradient let's
say you have a higher concentration
above and I'm going to say some
arbitrary some arbitrary particle has a
higher concentration above than it does
below they can actually attach
potentially or be or kind of get into a
compartment over here and then that
would trigger the carrier protein to
change its shape so that and let me see
if I can draw it's changed shape well so
it could change its shape so this is
when it's taking stuff from above and
then and then when it sees that hey I've
got stuff here it can let me it can
change its shape to look something like
this so it could kind of flip around let
me get the other tool it could whoops
really having trouble with my tools
today all right all right it could flip
around like this so before is open to
the top but now it could flip around and
the stuff that had just collected from
the top could be dumped inside inside
the cell and once again this is passive
transport because it's all about things
moving down their concentration gradient
if there was no cellular membrane here
these things would have moved in this
direction you would have had more things
moving in this direction to give an
amount of time than you would have had
things going in the opposite direction
but the cellular membrane was getting in
the way
but then this carrier membrane can
facilitate that passive transport it can
facilitate the actual diffusion