ENZYMES
UNIT II RESPIRATION & PHOTOSYNTHESIS
ENZYMES
 3-D shape
 Active site- enzyme
interacts with substrate
(lock and key)
 Lowers EA (activation
energy),
 Speeds up reaction
Enzymes
ENZYMES ARE CATALYSTS
 Catalysts= chemical that affects the speed a
chemical reaction happens without being used up
in the reaction
 Enzymes can speed up or slow down how fast a
reaction happens
 They only work on reactions that would happen
anyway In other words, they do not cause the
reaction to happen.
ENZYMES ARE PROTEINS THAT HAVE A VERY SPECIFIC
FUNCTION AND ONLY WORK FOR SPECIFIC
REACTIONS.
 Reactions need a certain amount of energy to
happen= Activation Energy (EA)
 Ex: Boulder on top of the hill
 This energy is called causes the reaction to
proceed
 Enzymes reduce the amount of activation
energy needed
Reaction
without
enzyme
EA without
enzyme
EA with
enzyme
Reactants
Net
change
in energy
(the same)
Reaction with
enzyme
Products
Progress of the reaction
ENZYME SHAPE
 Enzymes have specific shapes, which enable them to attach
to certain molecules, which are called “Substrates”.
 The point of attachment is called the “active site.”
 The active site is usually a groove or pocket which fits
with a certain enzyme shaped like a puzzle piece or
handshake.
 Once the reaction happens, the enzyme detaches from the
substrate and is used again for another reaction of the same
type.
“ASE”= ENZYME SUFFIX
 Enzymes are generally named after the molecule it works on
by changing the last three letters to “ase”.
 Example: Enzyme Sucrase, (breaks bond between
glucose and fructose in sucrose)
 Sucrose acts on the substrate sucrose breaking it into 
Glucose + Fructose
 Sucrase Only works on sucrose and no other
disaccharide.
3 MAJOR THINGS WILL AFFECT HOW WELL AN
ENZYME WORKS:
 Temperature
 Most enzymes work best in a certain temperature range
 Most humans enzymes work best between 35-40 degrees C (Around
human body temperature)
 pH (acid or base)
 Most human enzymes work best between pH 6 and pH 8
 Enzymes in the human stomach work best at acidic levels (ph 1-2) due
to presence of stomach acid used in digestion.
 Salt content in environment
 Excessive salt content can interfere with active site function.