Hi. It's Mr. Andersen and in
this video I am going to talk about the operon. The operon was discovered in the 1960s by
three French scientists. Jacob, Lwoff and Monod. That's really bad French. But they
got to coin the term operon. And basically it means to operate. And so it's mostly found
in prokaryotic cells. Mostly found in bacteria. There's a few eukaryotic operons but in general
it's just going to be found in bacteria. And so it led to other terms you maybe never heard
of before. Like regulons and modulons and stimulons. Stimulons are groups of operons
operating together from one stimuli. And so it just means to operate. That's what an operon
means. And so the one that they discovered was the lac Operon. They were studying this
in e. coli. And so the lac Operon is designed for e. coli to breakdown lactose. So lactose
is going to be a disaccharide. And remember if you're a bacteria living in our gut, you're
eating whatever we're eating. And so as the material moves down through our digestive
system, they have to be ready to quickly shift, depending on what the food is. If it's sugar
they have to be able to breakdown the sugar. If it's proteins, they have to be able to
break it down into amino acids. And if it's a disaccharide in this case, they have to
move it into the cell and then break it down and chemically digest it. And so they use
a lac Operon to do that. Now this is a picture of "Prog". But that's not how you spell Prague.
But it is the way that I remember the parts of an operon. You've got a promoter, a repressor,
an operator and then genes. And so if you can remember "Prog", it's going to get you
half of the way there to remembering how an operon works. And so the neat thing about
bacteria is that if they have a number of different genes that are used to achieve a
certain task, they'll put them right next to each other. And so as the RNA polymerase
moves down the DNA and makes all of the messenger RNA and makes all of the proteins, you're
just ready to do whatever the job is. And so the genes are going to be located right
next to each other. In this case, in the lac Operon to deal with lactose. What else do
we have? Well we've got the promoter. The promoter's going to be the region of the DNA
where the RNA polymerase can grab on to the DNA. We also have an operator. And so think
of that like an off switch that's going to turn on or off the operon. And then the lat
thing we have is a repressor. And so this is a lac Operon. It's Prog. It's promoter,
repressor, operator and then all of the gene. And so what are we trying to breakdown? We're
trying to breakdown lactose, or deal with lactose. Remember lactose looks like this.
It's a disaccharide. But in this little model right here, we're going to represent it as
a little pentagon. A yellow little object that look like this. And so all of a sudden
a lot of lactose is present. So what is the lac Operon going to do? Well it's going to
deal with that lactose. And so all of this lactose is moving around remember, but eventually
one of the molecules is going to bump into the repressor. As it bumps into the repressor,
it's going to change the shape of that repressor. And so a quick digression, everything, promoter,
operator and genes are DNA. So they're going to be part of the DNA of the bacteria. But
the repressor is a little bit different. It's a protein. It's a protein that came from a
different part of the DNA. There's going to be a regulatory sequence either upstream or
downstream of the operon that creates the repressor. It plugs in nicely to the operator
but once the lactose fits inside it, it's going to change the shape of that repressor.
What does that do? Well it opens up a region where that promoter can allow the RNA polymerase
to get on. And then that RNA polymerase is just going to drive right down the DNA. It's
going to make a bunch of RNA. It's going to make a bunch of those proteins. What are the
proteins designed to deal with? Lactose. And so they're going to breakdown the lactose.
Now all the lactose is gone. What's going to happen to that repressor? It's going to
return to its original shape. And that shape is going to fit into the operator. And so
if there's no lactose present, we would say the operator is in the off position because
the repressor is activated. It's activated. It's sitting inside the operator. It's physically
breaking the movement of that RNA polymerase. The RNA polymerase can't move down and code
for those genes because the repressor is sitting in it's way. What happens next? Well lactose
shows up again. Lactose would move into the repressor, free it up and then it's going
to be able to make those genes. And I've got a simulation at the end of this video that
shows you in a little more detail how that takes place. Before we get there, I want to
talk about the trp Operon. The trp Operon does essentially the opposite of that. So
the trp Operon is evolved in bacteria to deal with tryptophan. Or more specifically to deal
with the absence of tryptophan. So tryptophan is going to be an amino acid. And it's required
to make proteins. It's one of those 20 essential amino acids. And so the trp Operon basically
is designed to make tryptophan if it's not present. And so we're going to get tryptophan
in, you know in poultry, in milk for that matter. There's going to be high levels of
tryptophan. But if a bacteria does't have tryptophan, there's a number of different
genes that are required to make it. And so they can make their own. And so we've got
an operon called the trp Operon. How does that work? Well again we've got "Prog". We've
got our promoter, our repressor, our operator and then our gene. But if we have tryptophan
present, so tryptophan's going to be these yellow hexagons. If we have tryptophan, tryptophan's
going to fit inside the repressor and it's going to change its shape so that it fits
in the operator. And so in this case, if we have a bunch of tryptophan present, then we
don't want to make tryptophan. And so the repressor is going to set that operator to
the off position. What happens if all of a sudden the tryptophan goes away? If there's
no tryptophan in the diet? Well the bacteria is not out of luck because it changes now
the shape of that repressor. And so once it's changed the shape of the repressor, RNA polymerase
can grab on, drive down that operon, make all of those genes and those genes can be
used to create more tryptophan. And so it's a great kind of a feedback loop. So in a lac
Operon we're going to turn it on if we want to breakdown lactose. In a trp Operon, what
we're going to do is create tryptophan if we don't have it or if it's not present. And
I really didn't' understand how operons worked until I stopped thinking like a scientist
and really started thinking like an engineer. We've got a problem that we have to solve,
and one of the great ways that we can do that is using an operon. And so I'm going to show
you a quick simulation of how this works. It's a phet simulation. Here's a website.
I'll put a link to the simulation down in the video description down below. But it's
a great way, and I've used it with my students, for them to wrap their head around how an
operon works. And so we're looking at a lac Operon. And to make it simple, we're only
dealing with one gene. On of those three genes that are found. And so if we were to look
at the simulation, you could try to figure out what everything is. But it's easier if
I show you the legend and show you what everything is. And so we've got RNA polymerase kind of
bouncing around here. Again, they'd be moving around. There's molecular motion. They'd just
be randomly bouncing around. But this is one of the players. We've got the RNA polymerase
right here. We could look down below and I could ask you, now where is the operon? Is
this the operon here? Or is this the operon? Well the right answer is this. This is going
to be the the operon here because it's got a promoter. So let's put that promoter out
here. It's got an operator, an on-off switch. And then it's going to have a gene. In this
case the lacZ gene. So what's this up here? Well this is not an operon. But this is going
to be another, what we call a regulatory sequence. And so this one down here is going to make
an enzyme that's going to breakdown lactose. But what's this RNA polymerase up here going
to make? Well it's coding, it's making a little bit of messenger RNA. Well what it's eventually
going to make, is it's going to make a repressor. Okay so now we've got the fourth part of our
operator. We've got the promoter right here. We've got the repressor. We've got the operator.
And now we've got the gene. But you can see that the RNA polymerase can't make that gene
because the repressor is blocking its way. And so it's in an off position at this point.
And it should be. In other words we shouldn't start making those genes until lactose is
present. And so let's add a bunch of lactose. So I'm going to add a bunch of lactose here.
And let's watch what happens. Well if we add a bunch of lactose, and we could speed up
the simulation a little bit, what's going to happen is the repressor, and I could pause
it right here. That repressor is now having the lactose bind to it. And it's changing
it's shape. Or it's changing it's confirmation. Once the lactose, and you can see it's happened
in two cases, once the lactose binds to the repressor, it can't bind to the operator anymore.
And so if we play the video, what's going to happen. Well now RNA polymerase can drive
down the operator, or excuse me down the operon. It can produce a protein. In this case that's
going to be a lacZ protein. What's it going to do? It's going to digest and breakdown
all of the lactose that's present. And you can see that it's gobbling up all of those
lactose. The only lactose left is those that are bound to the repressor itself. What happens
eventually? All of the lactose is going to disappear. In other words we will have broken
it down. What happens now? Well that repressor is going to bind to the operator again. And
now we can't make that protein to break it. And so it's a wonderful feedback loop. It's
a feedback loop that deals with a bunch of lactose present. Because e. coli would be
silly to make all of the proteins to break it down until we've got a bunch of lactose
present. And so that's an operon. What is it again? It's all of the genes and then a
way to control those genes in one tidy little package. And I hope that was helpful.
