Download ENZYMES

ENZYMES
BEGIN
Hello there young students. I am Speedy Gonzalas, the fastest mouse in all of Mexico
and I am here to present, to you the information about ENZYMES!! Because I am so
fast, I will be personifying the enzyme, a type of biological catalyst. A catalyst speeds
up a chemical reaction without being used up the process.
Enzymes are proteins and are essential for the conduct of all the chemical reactions in
your body!
The progression of many chemical reactions is very slow.
Many are so slow that it appears that they do not occur at all
even though they are classified as spontaneous reactions.
Now compare this to my cousin, Slowpoke
Rodriguez. He moves around really slow almost
like he is not moving at all, but actually he is
moving.
The spontaneous chemical reaction occurs
without the requirement for outside energy.
The laws of thermodynamics tell us what will or
will not happen but do not tell us THE RATE!!.
If the reaction is:
EXERGONIC-; will happen with energy release or
ENDERGONIC- will not happen and require an
input of energy.
Now my cousin, he is exergonic, it’s just that he is
very slow. So he is a slow EXERGONIC REACTION.
SPONTANEOUS ≠ QUICK
SPONTANEOUS = -ve ΔG
Ea
The graph above shows an
exergonic reaction (-ve ΔG) as
energy is released. This reaction
occurs spontaneously, but the Ea
forms a barrier that determines the
rate.
Some spontaneous reactions are quick, like a dynamite
explosion, but some are slow like the rusting of a car.
Better watch out cat!!
Don’t confuse them with the NON SPONTANEOUS
REACTIONS
SPONTANEOUS REACTIONS are
exergonic and increase a system’s
entropy
NON SPONTANEOUS REACTIONS require an input
of energy to the system.
Where I come in is when you look at the activation energy
called Ea in the diagram.
The activation energy is like a little hill of energy
that is required to get the reaction started. Think of
it like the story of the little engine that could
Sucrose
Ea
Δ G is
negative
-7 kcal/mol
Glucose + Fructose
Going uphill is tough on the little engine. That is where I can
help. You see the hill is the result of the activation energy Ea
and I Speedy Gonzales am acting as an enzyme.
Ea
In this graph sugar in
the presence of
oxygen should burn.
We know this does
not happen unless
we start it on fire.
Lighting the match
corresponds to the
Ea required.
What I do is reduce the activation energy required for the
reaction to occur. THE Ea BECOMES LESS!!
Take a look at what the action of an enzyme like me does to
the graph.
When I do this
the reaction
speeds up!
Ea is lower here
The little engine
does not have to
go up such a big
hill with me there!!
Take a look at this graph again. If you did not have me, you would have to
start this reaction with energy as hot as fire. Your cells could not handle
that. In addition, my enzymes allow for control of these chemical
reactions in a process that is regulated by each enzyme. Combustion, like
the burning of fuel in your car engine is much more controlled here with
only small amounts of energy released at a time.
Ea
Ea requires lit match to start
How do I lower the activation energy you may ask. Well I act
to attach the substrate (that is the chemical from the reaction
side of the equation) by my special shape. Where we attach is
called the active site and each enzyme is specifically designed
to have its tertiary structure correspond to match the shape of
the substrate at this location.
NOTICE: the
enzyme active
site exactly fits
the substrate.
It is called the
LOCK and KEY
MODEL
There are almost an infinite number if different shapes that I can make
when you put me together with different amino acids in different orders
and there is no restriction on the length of the amino acid primary
structure! This means I can be made to fit any shaped chemical you want!
What I do is when I attach to the substrate I stress the
bonds a little bit. It is kind of like taking a toothpick and
bending it. Once it is bent, not much energy is required to
break it completely.
Toothpick bent-Bonds
are stressed
Did you ever hear of the straw that broke the camel’s back?
That can be compared to how I act. The camel is already
loaded up to full capacity. (bonds are stressed) All that
needs to be added is a tiny amount of weight to break the
camel. So when I act, very little energy is required to break
the bonds
If the
glove
don’t
fit you
have to
acquit
Represents the small amount of
energy to get the reaction to progress.
NOTE: the lock and key model has been replaced by
the INDUCED FIT MODEL shown here on the side.
The difference is that in the induced fit model the
active site changes shape to fit the substrate, much
like a glove fits your hand when it is put on.
LOCK AND KEY
INDUCED FIT
In the induced fit model, the substrate is bound to the active site with
HYDROGEN BONDS or IONIC BONDS.
Whether the enzyme catalyzes the forward or reverse reactions is
dependent on the concentration of products and reactants and the
ΔG. Remember they catalyze toward equilibrium
You know
señor , that
if you give
me more
substrate, I
will work
even faster!
Increasing the amount of substrate will increase the rate of reaction
up to a point of saturation. At this point all the enzyme molecules
are saturated with substrate and working at full speed. The rate
cannot be increased beyond this unless more enzyme is added.
I have a very important request to ask of you señor.
Please do not expose me to the following extreme
conditions or I will no longer be able to function!
No extreme temperatures
No extreme pH
No extreme salt concentrations
Exposure to these conditions can lead to DENATURATION of the ENZYME. If this
happens the enzyme will cease to function. The reason is that the protein will
undergo an irreversible conformational change ( big words that mean a
permanent change in shape). See the example of what happens to the egg
albumen (that’s the egg white) when exposed to high heat as shown below.
Uncooked albumen Cooked albumen
– a clear liquid
-a solid white mass
Please do not cook or
denature me in any way
señor. You need enzymes to
do digestion, metabolism..
The list goes on and on.
And Now for some enzyme facts for all you people out there!
Enzymes are specific – their shape only
allows them to attach one particular type of
substrate shape. Hence we need different
enzymes for each different chemical.
Enzymes are reusable – they speed up the chemical
reaction but are not used up in the process and can
be used again and again!
Enzymes always catalyze the reaction in the
direction of equilibrium.
Enzymes can be denatured (activity destroyed
permanently) due to extreme temperature,
pH or salt concentration.
Now, lets talk about factors that affect the
rate of enzyme activity.
TEMPERATURE- enzyme activity slows if it is too hot or too cold
pH - enzyme activity slows if it is too acidic or too alkaline
Concentration of Enzyme
More enzyme= faster rate Less enzyme = slower rate
Concentration of Substrate
More substrate = faster rate to saturation
Less substrate= slower rate
Presence of activators will increase rate
Presence of inhibitors will slow rate
Lets talk TEMPERATURE!! Take a look at the graph below señor. The black
line represents activity for a human enzyme at various temperatures.
OPTIMAL TEMPERATURE occurs at about 37 0 C .
Now compare that to a bacteria that naturally lives in hot springs, like those
in Yellowstone National Park.
OPTIMAL TEMPERATURE occurs for these at about 79 0 C and they need
special unique enzymes to function at this temperature. See the
presentation on the first cells (Evolution) to find out more
That’s
the
idea.
Why don’t you go for a
dip in the hot tub filled
with natural hot spring
water
The OPTIMAL TEMPERATURE is the temperature at which the enzyme works the
best. You would expect a human enzyme to function best at body temperature.
Enzyme activity should drop off if the temperature becomes too hot or too cold
That
water is
much too
hot. I’ll
cook at
790 C.
THE HOT TUB ISSUE -- ARE THEY SAFE OR A BREEDING GOUND FOR GERMS?
Hot tubs operate by circulating water at temperatures close
to body temperature.
The optimal temperature for the growth of infectious microorganisms of humans is also body temperature. Their enzymes
work the best at this temperature.
Hot tubs are maintained with the chemical fluorine rather than
the weaker chlorine to try to kill these micro-organisms.
Water is a method of transfer of infection in humans. The
water can even have microbes that infect the skin such as the
bacteria Pseudomonas aeroginosa which cause HOT TUB
FOLLICULITIS. The bacteria infect the hair follicles resulting in a
rash that usually lasts about a week.
Oh I absolutely
guarantee it
Now can I trust
that there are no
Boiling the water will kill
bacteria in your hot
these bacteria as their
tub ?
enzymes denature.
Let’s take a look at the effect of
pH on enzyme activity.
You can see from this graph that
there are two very different
enzymes being compared.
Trypsin is shown in red and
functions at a pH optimum of
about 8. If the pH falls below 6
or above 10 the enzyme stops to
function. Trypsin functions to
digest proteins in the small
intestine and the pH there is 8 so
it works very well in this
environment.
The enzyme pepsin is shown by the black line and it has a very different optimal pH. This is
because it is an enzyme that functions in the stomach. When we digest our food, the
stomach fills with HCl acid. This lowers the pH down to 1 or 2 and causes the pepsin to
work. If the stomach stops making acid, the stomach pH rises back up to 7 and the pepsin
stops working. This is important to control pepsin from digesting the stomach lining.
DID YOU KNOW?
If the acid is present without
food, the enzyme pepsin will
become active and begin to
destroy the stomach lining.
This can lead to open sores in
the stomach. These sores
(called ulcers) bleed and
cause stomach pain. Normally
the pepsin is not activated if
there is no food because the
acid is not produced.
Stomach acid is made when you eat or are
stressed.
It will lower the pH to 1 or 2
Pepsin will become active and begin to digest
any meat inside the stomach
The stomach walls are protected from this
digestive mixture by a layer of mucus.
The entire stomach lining is replaced every
three days
What’s the matter
señor stomach. You
don’t look so good.
I think I have an
ulcer. Where is
the antacid?
Interested yet? See
the DIGESTION
presentation for
more details.
Every three
days. I think it is
sooner if you eat
Mexican food.
It should be pretty obvious that the more
enzyme there is the faster we will speed up
the reaction rate
INCREASING ENZYME (CONC.) SPEEDS UP THE REACTION RATE!!
Arriba! Arriba!
Ándale!
There are too many mice all going too fast. You can’t
expect me to catch them!
Arriba! Arriba!
Ándale!
Yii-hah!" "Hello,
pussy cats! You
looking for a nice
fat and slow
mouse for
deenner? ...
Look somewhere
else!
We mice love cheese. Now if we pretend that the cheese is
the substrate, I can tell you that we will work very hard to
eat it ( I mean catalyze it) for you. The more cheese you add
the harder we will work until all the enzymes are working to
full capacity. This would be the point of saturation.
THE MORE SUBSTRATE( CONC.), THE FASTER THE REACTION RATE!!
Arriba! Arriba! Andale! Andale!
YEEHAH! ....Hey Pussy cat, we have
no time to play we are all busy
working to move this cheese!
That’s right. Every one
of us is busy with the
cheese!!
Sometimes we enzymes need something to make us the
proper shape or enable us to complete the catalysis.
Allosteric activators --- cause the enzyme to only become the proper shape (
and thus active) when an activator is present. The activator attaches to
locations on the protein that will cause it to change its overall shape, yet not
interfere with the active site. It is a method of controlling the enzyme and
when it works. In this case you have to have the ACTIVATOR PRESENT for the
ENZYME to WORK.
Active site will
not fit substrate
In this example
the substrate
acts as the
activator
Active site will now
fit the substrate
There are also
allosteric
inhibitors. The
ALLOSTERIC
INHIBITORS
can be used to
shut the
enzyme down
when they are
present.
ALLOSTERIC =
CHANGE
SHAPE
INHIBITOR when
present, it changes the
active site making it
inactive
Sometimes we are trying to work and
something gets in the way. Another
chemical bonds to the active site of the
enzyme. This prevents us from bonding to
the proper substrate and doing our job.
These chemicals that interfere are called
inhibitors.
Here the
substrate
competes with
the inhibitor for
the active site
COMPETITIVE INHIBITOR
Substrate conc.
You can see
from the graph
that if you add
enough
substrate the
effect of the
inhibitor is
minimized
NONCOMPETITIVE INHIBITOR
Here the substrate
inactivates the
enzyme active site
by binding
another site.
From this graph you
can see that
enzymatic action is
decreased no matter
how much substrate
is present
Substrate conc
You can use competitive inhibition to minimize
the effects of a toxin or poison. Take a look at
this example that Speedy found out about!
I heard something about drinking ethanol to
treat methanol poisoning. I never knew why,
but now I see. The ethanol and methanol
both compete for the same active site on the
enzyme. If only methanol were present, the
enzyme would be more adversely affected.
Adding the ethanol slows down the enzyme
ability to bind to methanol.
Now given the following enzyme graphs, tell me where you
would expect each to have the fastest reaction rates
CHYMOTRYPSIN?
Fastest reaction at optimum
pH 8
CHOLINESTERASE?
Fastest reaction above pH 7
PEPSIN?
Fastest reaction at optimum
pH 1.8
PAPAIN?
Reaction rate constant
pH 4 — pH 8
Well that is enough about enzymes and
rates of reactions. Now lets talk about some
of my helpers or COFACTORS.
You might sometimes take vitamins or
certain on protein organic molecules.
These are COENZYMES. Many enzymes
combine with these for catalytic activity.
You might take minerals also. If I use an
inorganic mineral like copper, iron or zinc to
make the enzyme functional, the mineral is
called a COFACTOR.
Take your vitamins
kids.
The last thing I have to talk about is feedback inhibition and
enzymes.
Metabolic pathways are
commonly regulated by
FEEDBACK INHIBITION in
which the product of a
pathway acts as an
allosteric inhibitor of an
enzyme early in the
pathway.
Well I hope you learned something from
my presentation. I have to go now.
Arriba! Arriba! Ándale!
Yehaw!...
Enzymes
The end