Enzymes
Energy In Reactions
• Energy is released or
absorbed whenever
chemical bonds are
formed or broken.
• Because chemical
reactions involve
breaking and forming
of bonds, they involve
changes in energy.
Catalyst
• A catalyst is a
substance that speeds
up the rate of a
chemical reaction.
• Catalyst work by
lowering or reducing
a chemical reaction’s
activation energy.
• Activation energy =
energy needed to
drive or start a
chemical reaction
Let’s say this
is a bonfire at
our next rally…
Notice that without the enzyme it takes a lot more
energy for the reaction to occur. By lowering the
activation energy you speed up the reaction rate.
Enzymes
• Enzymes are proteins that act as biological
catalysts. Heat is a catalyst but not an enzyme!
• Cells use enzymes to speed up chemical
reactions that take place in cells (metabolism) .
All life would not exist without enzymes –
Reactions would take too long!
• Enzyme speed up reactions by lowering the
activation energies.
• Enzymes are highly specific - because a
particular enzyme catalyzes only one reaction,
there are thousands of different enzymes in a cell
catalyzing thousands of different chemical
reactions
Naming Enzymes
• Most enzymes end in “–ase”
• Sucrase will only break down sucrose
(table sugar - a disaccharide)
• Lactase will only break down lactose
(milk sugar)
• Some retain “old” names like trypsin,
which digests proteins in the stomach.
Structure of Enzymes
• Enzymes provide a site
where reactant(s) can be
brought together to react.
• It is called the active site.
• Such a site reduces the
energy needed for a
reaction to occur.
Active site
• All enzymes have an active site, where
substrates are attracted to.
• Enzymes are NOT used up when
catalyzing a reaction, so they can be
used over and over again.
Substrate
• The substance changed
or acted upon by an
enzyme is the substrate.
• Substrates are the
reactants of a chemical
reaction.
The Enzyme Substrate complex
• The enzyme forms a
temporary union with the
substrate.
• The 3-D shape of the active
site changes to match the
substrate’s shape.
• Once the substrate and
active site meet a change in
shape of the active site
causes a stress that changes
the substrate and produces
the end product(s).
Which one will fit ?
• Enzymes are highly
specific.
• Only one substrate
(reactant) will “fit” into
the active site.
Factors that affect enzyme activity
• pH
– Some enzymes work best in either an
acidic or basic environment. The stomach
is acidic but the small intestine is basic.
• Temperature
– High Heat can change the 3-D shape of an
enzyme. This is called denaturation.
• Amount of substrate
– Concentration of enzyme or substrate can
affect reaction rate.
Effect of temperature on an enzyme
• If temperature is too
high or too low the
enzyme may get
denatured.
• Now the substrate will
not fit into the active
site.
• No reaction will occur.
How pH affects an enzyme
• If the pH is to high or
low the enzyme will not
work, because its shape
will change.
Effect of pH
• All enzymes have an
optimum pH that they
function best at.
• If the pH is too low or
too high the enzyme
will work slowly or not
at all.
• The shape of the
enzyme changes,
making it harder for
the substrate to fit in.
Analyze the graph at what ph does
Chymotrypsin function best?
Temperature
• Most enzymes have an
optimum temperature range
in which they work best.
• As the temperature rises the
enzyme and substrate
molecules move quicker
causing more collisions to
occur so the reaction rate
increases.
• If you the temperature gets
too high the protein can be
denatured.
What is the optimal tempeerature
for this enzyme
Amount Of Substrate Present
• At low substrate
concentrations, collisions
between enzymes and
substrate molecules are rare
and reaction rate is slow.
• As the amount of substrates
increases, so do the
collisions between enzymes
and substrates, and the rate
increases.
• This continues until the
enzymes are saturated with
substrates or working as fast
as they can!.
The End!