A catalyst lowers activation
energy
I.
Activation Energy
a.
Remember, activation energy for a chemical reaction is
like the energy that is needed to push a rock up a hill.
i.
ii.
When enough energy is added to get the rock to the top of
the hill, it can roll down the other side by itself.
Chemical reactions are similar- once it starts, it can
continue by itself and at a certain rate.
b. Often, the activation
energy for a chemical
reaction comes from
an increase in
temperature. But
even after the
reaction starts, it may
happen very slowly.
c. Reactions often need a catalyst, which is a
substance that decreases the activation
energy (the hill!) needed to start the
reaction, and also increases the rate of the
chemical reaction.
d. Catalysts are not considered reactants or
products because they are not changed or
used up during a reaction.
Enzymes allow chemical
reactions to occur under tightly
controlled conditions
I.
Enzymes
a.
Chemical reactions in organisms have to
take place at an organism’s body
temperature, so adding heat to speed up
the reaction would disrupt homeostasis.
So a catalyst is needed, since these
reactions often have to happen quickly.
b. Enzymes are catalysts for chemical
reactions in living things. They lower the
activation energy (the hill!). They do not
change the direction of the reaction- they
just change the amount of time needed
for equilibrium to be reached.
c. Enzymes are
involved in
almost every
process in
organisms.
From
breaking
down food, to
building
proteins,
enzymes are
needed.
d. Almost all
enzymes are
proteins.
II.
Certain Conditions Can Disrupt Enzymes
a.
b.
Each enzyme depends on its structure to function properly.
Conditions such as temperature and pH can affect the
shape and function of an enzyme. Too high or too low a
temperature can disrupt the enzyme. The same is true for
pH. Most human enzymes work best at body temperature,
and at a neutral pH. This is one reason why a high fever is
so dangerous to a human.
III.
Each enzyme’s shape
allows only certain reactants to bind to the
enzyme. The specific reactants are called substrates.
b. Substrates temporarily bind to enzymes at specific
places called active sites. Like a key fits into a
lock, substrates exactly fit the active sites of
enzymes.
Lock-and-Key Model:
Substrates bind to an
enzyme at certain
places called active
sites.
The enzyme brings
substrates together
and weakens their
bonds.
The catalyzed reaction forms
a product that is released
from the enzyme.
c. The lock-and-key model helps explain how
enzymes work.
i.
First, the enzyme brings the substrates
(reactants) close together.
ii. Second, enzymes decrease activation energy
because they put the substrates in a position that
strains their bonds, making the energy
required to break the bond less.
Substrates bind to an
enzyme at certain
places called active
sites.
The enzyme brings
substrates together
and weakens their
bonds.
The catalyzed reaction forms
a product that is released
from the enzyme.
IV.
Inhibitors
a.
b.
c.
Sometimes there
are inhibitors that
disrupt an
enzyme’s function.
Competitive
inhibitors mimic the
substrate and
block the active
site.
Non-competitive
inhibitors bind to
somewhere on the
enzyme other than
the active site,
changing the
shape of the
enzyme.
V.
Other Things That Affect Enzyme
Activity
a.
b.
Substrate concentration- sometimes adding
more substrate will speed up the reaction,
but only to the point at which all enzymes
are being used.
Enzyme concentration- sometimes adding
more enzyme to the reaction will speed it
up.