Now if we want to think about a reaction that's in biology
that we have already taken a quick look at,
we'll look at this bicarbonate buffering system.
If we have carbon dioxide and water coming together,
they require an enzyme called carbonic anhydrase
to put the two molecules together and form carbonic acid.
Once we form carbonic acid, it is a reversible reaction, so we
could go back the other way and get the original substractes back.
So pretty much all reactions are reversible.
Although on occasion, we'll run into a reaction in which
the activation is so big, we can not even overcome it.
But theoretically, they could be reversible.
So the rate of activity of enzymatic reactions really depends on
substrate concentration up to a certain point.
So here's an example bar. If we have a certain number of enzymes,
and a certain number of substrates,
those enzymes will bind substrates,
and the more the substrate there is, the higher the reaction rate,
up till a certain point at which each of the enzyme is full
and then we max out.
An anology here would be that if I were trying to catch tennis balls
and put them in a basket down here on the floor,
I could catch a certain number of tennis balls
and I can work fairly quickly,
but if I receive too many tennis balls,
they are going to start falling all over the place
and I can only work at a certain rate.
So the enzyme activity is restricted or limited by the concentration
of enzymes or the number of enzymes available to do the work.
Cells can increase the number of enzymes
to increase the rate of reaction
and a number of signals can happen, more and more and more signals,
but it's limited again by the concentration of enzymes
which is determined by the cell itself.
A couple of things that impact the rate of reactions,
we'll see also were involved in the denaturation of proteins.
If you recall, we have the influence of temperature.
If we heat up the temperature too much, proteins denature.
The active sites might change shape and not receive the receptor
or the signal molecule properly.
So all enzymes have an optimum temperature for functioning.
For example in humans, right around body temperature, all make sense.
However, there are some other organisms for example that living
hydrothermal vents in Yellowstone National Park, it's beautiful there,
but it's very very very hot. Some of these prokaryotic organisms
have to have enzymes that function at very high temperatures.
And we'll see an example of this when we look at DNA replication
and some technologies there we've taken advantage of,
an enzyme called taq polymerase from very hot environments,
we've stolen it from a prokaryotic cell.
So we'll see that later on.
Another impact would be pH. Again if we change pH, proteins change
shapes, so we have optimum pHs for the enzyme functioning.
For example, we consider the enzyme pepsin works in
a very acidic environment in the gastrointestinal system.
The stomach is very acidic, produces a lot of acid which if we had
a enzyme that function at our normal body pH would fall apart.
So pepsin has an ultimate functioning
at around pH high twos into threes,
whereas the enzyme trypsin functions
at a more normal body pH around 7.
So any enzymes working in the stomach
have to be set up for a very acidic environment.
Optimum functioning, otherwise the proteins change shape,
denature and don't work as efficiently.