Chapter 16.6 & 16.7
Enzymes & Enzyme Actions
SWBAT:
Describe how enzymes function as catalysts and give their names
Describe the role of an enzyme in an enzyme-catalyzed reaction
Introduction to Enzymes
Biological catalyst which speed up biological
reactions by lowering the activation energy
required for them to take place
Mostly made up of proteins
Mot used up or
chemically change
at the end of the
biological reaction
What is an enzyme?
Introduction to Enzymes
Can be used again and again
Produced only when needed
Catalyse reversible reactions
E + S
ES
EP
E + P
E = enzyme
S = substrate
P = product
How enzymes work?
Classification of Enzymes
Oxidoreductoases (Oxidation – Reduction)
Transferases (Transfer groups of atoms)
Hydrolases (Hydrolysis)
Carbohydrases, Proteases, Lipases
Lyases (Add/Remove atoms to/from a
double bond)
Isomerases (Rearrange atoms)
Ligases (Combine molecules using ATP)
Enzyme Action
Enzymes are globular proteins
Unique 3-D shape that binds to a small
group of reacting molecules called
substrates
Active Site
Area where the enzyme binds the
substrate and catalyzes the reaction
The active site of a particular enzyme fits
the shape of only a few types of substrates
Active Site
Substrate
Enzyme-Catalysed Reactions
Anabolic reactions
Synthesis is simpler substances into complex
substances
Amino Acids  Polypeptides  Proteins
Catabolic reactions
Breakdown of complex substance into more
simple substances
Hydrogen peroxide  Oxygen + Water
2 H2O2  O2 + 2 H2O
Characteristics of Enzymes
Speed up chemical reactions
Small amount needed to catalyse a
reaction because enzymes can be used
again and again
The shapes of the active sites make
enzymes highly specific, meaning they can
only interact with 1 type of substrate to
form an enzyme-substrate complex
“Lock and Key” Hypothesis
The active site of an enzyme molecule =
lock; substrate molecule that the enzyme
acts on = key
When the enzyme and substrate molecules
are bound together, they form an enzymesubstrate complex
“Lock and Key” Hypothesis (cont.)
Substrate molecule is subsequently
converted into products
Product molecules leave the active site
Enzyme molecule is free to bind with more
substrate molecules
“Induced Fit” Model
Enzyme molecule can undergo
adjustments at its active site
Binds more tightly with substrate molecule
Facilitates binding at active site and
speeds up rate of chemical reaction
Chapter 16.8
Factors Affecting Enzyme
Activity
SWBAT:
Describe the effect of temperature, pH, concentration of
substrate and inhibitors on enzyme activity
Factors Which Affect Enzyme Activity
Temperature
pH
Concentrations of substrates in enzymatic
reactions
Temperature
 Optimum temperature (37°C) – the temperature at
which an enzyme is most active (can catalyze the
most number of reactions per second)
 Rise in temperature (until optimum) 
Increase in enzyme activity
Kinetic energy of particles increases
Increases chance of substrate molecules fitting into the
active sites of enzyme molecules
More rapid formation of enzyme-substrate complexes
Increase in formation of products
Temperature (cont.)
When temperature exceeds optimum
temperature of enzyme activity, it starts to
fall rapidly
H-H bonds in enzymes
break, leading to the
denaturation of enzymes
Unique 3-D structure lost
Denaturation is
irreversible
pH
Optimum pH (~7.4) = maximum activity
Most enzymes lose their abilities to
catalyse reactions at pH 3 and pH 11
Extreme changes in pH of a solution will
denature the enzyme, just like temperature
pH (cont.)
Slight changes in pH is enough to change
the electrostatic charges of the active site
of enzyme and substrate
Electrostatic repulsion
occurs
Inhibits the formation of
enzyme-substrate
complex
Substrate & Enzyme Concentrations
 Substrate concentration increases  rate of
reaction increases
 Saturation of enzyme molecules (all being made
use of in reaction)
 Reaction cannot take place
 Increase in enzyme concentration will increase
the rate of reaction again
Animation
Animation comparing
Enzymes
Substrates
Inhibitors
Temperature
pH
Link to animation
Enzyme Inhibitor
Competitive Inhibition
Non-Competitive Inhibition