Hi. It's Mr. Andersen and welcome to biology essentials video number 36. This
is on the evolutionary significance of cell communication. In other words how cells talk
to one another. And so I want to start with one of my favorite stories of symbiosis. Symbiosis
is when two creatures are living together. And the examples I have here are Vibrio fischeri,
which is a bacteria, that can bioluminesce, in other words it can glow. And then this
is the Bobtail Squid. The Hawaiian Bobtail Squid. And what the Bobtail Squid can do is
it can actually bioluminesce as well. So it can glow. But the reason it can bioluminesce
is because it has these bacteria living inside it. And the reason it can bioluminesce is
if you're a fish looking at the Bobtail Squid from below, they can adjust the light so they
actually blend in with the sky. And so they're both getting something out of this relationship.
In other words the Bobtail Squid is feeding these bacteria. They're these little packets
of polysaccharides so they actually feed the bacteria food. And in return they get them
a place to live. And so cell communication is going to have different roles depending
on if you are single-celled or multicellular. So if you're single-celled you have to have
communication between all these bacteria. You have to be able to sense your environment
and you have to be able to communicate. If you're multicellular, then all the cells the
in organism have to be able to communicate and make sure that they're on the same page.
And so we find that the same signals that are found in bacteria are very similar to
the signals that are found in eukaryotes. And so in this video I'm really just going
to talk about two things. And that is how communication through signal transduction
pathways is conserved through evolution. And so in single-celled organisms it's a response
to the environment. An example I'll talk about is quorum sensing and so how bacteria can
tell otter bacteria how crowded it is. And then I'll talk about multicellular organisms.
How they can coordinate all of the activities. Example I'll give you is how epinephrine is
linked to glycogen breakdown and release of glucose. And so even though these are two
separate pathways, the pathway of the single cell, the pathway of the multicellular organisms,
we find that the signal transduction pathways, how they work, how they operate are almost
identical. And so that means they've been around a long time. They've just been co-opted
for different uses. And so let's start with the Vibrio fischeri which is a type of bacteria.
They have two different ways they could live. In the ocean if you are Vibrio fischeri living
by yourself, planktonically one bacteria by itself, we find that they don't glow. In other
words there's Vibrio fischeri everywhere in the ocean. They're all alone. They don't glow.
It's just dark. But if they live in a colony, if they live together and their numbers start
to get large, then they'll start to glow. And so in this Bobtail Squid they'll actually
live just in this eye pouch right here. And once you get enough of them in that eye pouch,
then they'll actually start to glow. And so how do they do that? How do they control that?
Well the use a signal transduction pathway. And so let's say this is one bacteria. So
this is one bacteria. And it's all by itself. But it will still be giving off proteins call
auto inducers. And so since it's one bacteria by itself and these are going to move just
through diffusion, the odds of that hitting another bacteria are really really low. But
let's say we add more bacteria. And let's say we add more bacteria and more auto inducers.
And then we add more bacteria and more auto inducers, eventually what's going to happen
is that those auto inducers are going to be picked up by other bacteria. That's going
to set up a signal transduction pathway. In other words a series of chemical reactions
that cause them to do something. In this case they cause them to produce a protein. In other
words they're going to transcribe a gene and actually make a protein. And if we're talking
about this glowing bacteria, it'll actually make a protein called luciferase. Liciferase,
and you can also tell that if it ends in a s e it's an enzyme. Luciferase is an enzyme
and it breaks down luciferan and it makes this glow. And an example of where you'd see
that, if you've ever seen a firefly it's the same enzyme. Luciferase breaking down luciferan
is actually make that glow. That luciferase will blend, or excuse me, will move through
diffusion. It triggers this cascade. So this would be a positive effect or a positive feedback
loop. And now all the bacteria are going to glow. Now let's say our numbers start to drop
off. We're going to have less autoinducers. We're going to have less luciferase and we're
not going to have that glow. And so quorum sensing is a quick way for bacteria to see
how many bacteria are there around. But the can also see, they can sense motion, they
can sense chemistry. And the more we learn about bacteria, the more we're starting to
realize that they're communication between bacteria is really sophisticated. It's just
as sophisticated as the communications we would have in eukaryotes. And so what are
the constraints in eukaryotes? In eukaryotes we have to get a message out and we have to
get all of our cells to operate together. And so the best system inside our body that
explains this would be the endocrine system. And so one of the best glands that we have
sits right on top of the kidneys. It's called the adrenal gland. And in the center of that
you have what's called the adrenal medulla. And so that's going to get a message that
comes from the brain. And that's called the fight or flight response. That fight or flight
is going to cause the cells in the adrenal gland to secrete a chemical called epinephrine.
Now this looks a lot like the auto inducers that were secreted by the bacteria. And they
do the same thing. That epinephrine is going to set up a signal transduction pathway in
all the cells. And so remember fight or flight response is when there's danger and then you
have to respond to that. An example is you have to get a bunch of blood sugar so we can
start making ATP so we can respond. And so by releasing all that epinephrine it sets
up a signal transduction pathway. In other words, a cascade of events inside the cell.
And I've talked more about how it uses cyclic AMP. But what it eventually does is cause
transcription of messenger RNA. The creation of an enzyme. In this case it's phosphatase.
And then the breakdown of glycogen to create glucose. Now we're looking inside the cell
and we're seeing how this addition of just this one chemical message, this one epinephrine,
can set up this signal transduction pathway to create a bunch of glucose. But this could
be luciferase as well that was created in those bacteria. In other words, we use communication
to sync single celled organisms with their environment and coordinate activities in eukaryotic
cells. And so that's cell communication, again found in all organisms. We're just starting
to unlock some of its secrets inside. And I hope that's helpful.