ENZYMES
• Perform chemical reactions in your body
• What type of food nutrient are they?
– PROTEINS
• Have to be folded up in a particular way in order
to work
• Name is based on the substrate it works on—
always ends in “-ase”
– Lactase works on:
• Lactose
– sucrase works on:
• Sucrose
– Protease works on
• proteins
ACTIVATION ENERGY
• Energy “hump” which molecules have to
get over in order to react
This reaction is
exothermic
because it releases
energy
The products have
less energy
than the reactants
Example: paper will not burn by itself – it needs an input of
energy to get over the energy hump, but once it starts it
releases energy
More about activation energy…
This reaction is
endothermic
because it absorbs
energy
The products have
more energy than the
reactants
Example: plants make their own sugars out of carbon dioxide and water
This is called PHOTOSYNTHESIS
The sugar (glucose) has more energy than the CO2 and H2O
Check your Understanding
1. Enzymes are what kind of food nutrient?
2. What is the difference between and
endothermic and an exothermic
reaction? Give an example of each
3. What does an endothermic reaction look
like on a graph? An exothermic reaction?
CATALYSTS
• Help reactions proceed faster than normal
– Lower the activation energy required for the
reaction
– Reactions can take place at a lower
temperature than normal
• Enzymes are the catalysts in your body
• Catalysts only help the reaction proceed,
but are not part of the final product—they
can be re-used
How enzymes work
• They bind to the substrate they are acting
on
– The substrate has an active site which
attracts the enzyme
– “Lock-and-key: model: active site and enzyme
have to fit exactly
– “Induced fit” model: the enzyme changes
shape slightly as it binds to the substrate
Induced-fit model of enzyme activity
Cofactors
• Some enzymes require a cofactor or a
coenzyme in order to work
• In your body, the cofactors are vitamins
and minerals
How enzymes are denatured
• Enzymes are very sensitive to changes in
pH and temperature
• They cause the enzyme to denature—the
enzyme unfolds slightly so its 3-D shape
won’t fit the substrate anymore
Check Your Understanding
1. Explain how enzymes work as catalysts
in your body
2. Explain the difference between the lockand-key model and the induced-fit
model of enzyme activity
3. What are the cofactors in your body?
4. What does denature mean? What would
cause an enzyme to become denatured?