First Five
 Explain the meaning of the following terms:
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enzyme
substrate
product
active site
denatured
What are Enzymes?
 Globular proteins that act as biological catalysts to
increase reactions rates
 Catalysts: substances that speed up reactions w/o being
consumed
 Biological? Because they are proteins; NOT because they
are alive (they aren’t!)
Enzymes: How they work
speed up biochemical
reactions by lowering
the activation energy
of reactions that would
normally happen
anyway.
Mode of Action
Enzymes bind substrates
(enzyme reactant) into active
sites (pocket or groove on
enzyme).
While the enzyme and the
substrate are joined, the
enzyme catalyzes the reaction
and converts the substrate to
the product(s).
Enzymes
 A classic example of an enzymatic reaction is the
hydrolysis of sucrose into glucose and fructose.
Enzymes
 Another look…
Practice
Find the enzyme, substrate(s), and product(s) in the sentences.
I) Acetylcholinesterase breaks down acetylcholine into acetyl and choline.
 Enzyme: ________________________
 Substrates: ______________________
 Products: _______________________
II) A disaccharide can be broken down into glucose and fructose by lysozyme
 Enzyme: ________________________
 Substrates: ______________________
 Products: _______________________
Practice
Find the enzyme, substrate(s), and product(s) in the sentences.
I) Acetylcholinesterase breaks down acetylcholine into acetyl and choline.
 Enzyme: Acetylcholinesterase
 Substrates: acetylcholine
 Products: acetyl & choline
II) A disaccharide can be broken down into glucose and fructose by lysozyme
 Enzyme: lysozyme
 Substrates: sucrose
 Products: glucose & fructose
Factors Affecting Enzyme Activity
Factors Affecting Enzyme Activity:
Rate of Reaction vs Enzyme Concentration
Describe the activity of
the enzyme as
Enzyme activity increases as
concentration
of the
enzyme
concentration
enzyme Eventually
increases.enzyme
increases.
activity plateaus even though
enzyme concentration
continues to increase.
Factors Affecting Enzyme Activity:
Rate of Reaction vs. Temperature
Describe the activity of
the enzyme as
temperature
increases.
Increasing
heat energy
causes
more collisions between enzyme
and substrate, until an optimal
temperature is reached.
Above the optimal temperature,
the enzyme denatures so the rate
falls rapidly.
Factors Affecting Enzyme Activity:
Rate of Reaction vs. pH
Describe the activity of
the enzyme as pH
increases.
Activity gradually increases
up to the optimal pH and
gradually decreases after
the optimal pH.
Effects on Enzyme Activity
Rate of Enzyme Activity is influenced by:
◦ Substrate concentration
◦ more substrate = more activity until saturation
◦ Amount of enzyme
◦ more enzyme = more activity until saturation
◦ Temperature
◦ higher temperature = more activity until the enzyme’s protein denatures
◦ pH
◦ usually in range of 6-8 for enzymes in humans
◦ Inhibitors
◦ reduce activity by binding or changing shape of active sites
Two types of inhibitors
 Competitive Inhibitor
 When something besides the
substrate blocks the active site
 Noncompetitive Inhibitor
 When a molecule binds to
another spot on the enzyme
causing it to change shape and
become inactive
Enzyme Simulation
 Rules:
 Only do your action upon your substrate.
 The starting substrate and ending product must match the picture on your
enzyme’s instructions.
 If you can’t operate upon a particular substrate, move it on to another
person or another table.
 Enzyme E is the last step in the process. Although the description
only shows two of the monomers stuck on the pencil, it will continue
adding more and more until it is full.