Enzymes
They make things, they break
things
Enzymes:
1. Function
2. Inhibition
3. Product Inhibition
4. Activators
5. Cofactors
What is an Enzyme?
• Most enzymes are globular proteins
– Definition: “A macromolecule serving as a catalyst,
a chemical agent that changes the rate of a reaction
without being consumed by the reaction”.
An RNase
Simulation:
• Observing an enzyme in action
• 18 volunteers (2 from each group)
• Chemical reaction simulation
Simulation:
• Test Reaction:
Method:
Enzyme Observations:
-
Enzymes:
• Not used up in the reaction.
• Make the reaction require less energy.
• One enzyme molecule can be a catalyst for
several reactions.
• Usually end in the suffix “-ase”. E.g. DNA
polymerase, ATP synthase, Ligase, Sucrase,
RNase, etc.
• The FUNCTION of an enzyme is often
indicated by the enzyme name.
Rate of Reaction:
• What would happen to the rate of reaction if
more substrate was added?
• What would happen to the rate of reaction if
more enzyme was added?
Why Enzymes?
Energy
required
for RXN
to occur.
Energy
required
for RXN to
occur IF
enzymes
used.
HEAT
Why Enzymes?
• Enzymes lower the required Energy of
Activation
• This allows for faster reactions
• This facilitates reactions that otherwise could
not occur as quickly
• Some enzymes can make reactions go trillions of times
faster
• Carbonic anhydrase (stomach) can catalyze over
1,000,000 reactions per second
• Some enzymes are temperature/pH specific.
A
B
C
D
Transition state
A
B
C
D
EA
Substrate
A
B
∆G < O
C
D
Products
Progress of the reaction
Course of
reaction
without
enzyme
EA without
enzyme
EA with
enzyme
is lower
Substrate
∆G is unaffected
by enzyme
Course of
reaction
with enzyme
Products
Progress of the reaction
How Do Enzymes Work?
http://www.youtube.com/watch?v=CZD5xsOKres
How Do Enzymes Work?
• Orienteer:
– Active site encourages
substrates to come together
in the correct orientation
• Stressor:
– Induced fit stresses and
bends critical chemical
bonds.
• Good microenvironment:
– E.g. Active site is low pH.
• Direct contribution:
– Brief covalent bonds
between substrate and R
groups.
Substrate
Active site
Enzyme
(a)
Enzyme-substrate
complex
(b)
Sucrose + H2O + Sucrase 
Sucrase-Sucrose-H2O Complex 
Glucose + Fructose + Sucrase
1 Substrates enter active site; enzyme
changes shape such that its active site
enfolds the substrates (induced fit).
2 Substrates held in
active site by weak
interactions, such as
hydrogen bonds and
ionic bonds.
Substrate
Enzyme-substrate
complex
6 Active
site is
available
for two new
substrate
molecules.
Enzyme
5 Products are
released.
4 Substrates are
converted to
products.
Products
3 Active site can lower EA
and speed up a reaction.
Specificity
• Enzymes often catalyze only a single reaction
• Enzymes are typically very specific
• How many different kinds of enzymes are in
the human body?
Enzymes:
1. Function
2. Inhibition
3. Product Inhibition
4. Activators
5. Cofactors
Minute Paper
• What are the top three things you learned
about enzyme function?
Enzymes:
1. Function
2. Inhibition
3. Product Inhibition
4. Activators
5. Cofactors
Enzyme Inhibition
• Enzymes can be inhibited by compounds
– Inhibitor often similar in structure to substrate
• Enzymes can be inhibited at active site or a
different part of the molecule
– Allosteric inhibition
Enzyme Inhibition
Substrate
Competitive
inhibitor
Enzyme
Noncompetitive inhibitor
(a) Normal binding
(b) Competitive
inhibition
(c) Noncompetitive
inhibition
Enzymes:
1. Function
2. Inhibition
3. Product Inhibition
4. Activators
5. Cofactors
Product Inhibition Simulation:
- Within each group, designate THREE people as
enzymes (foldase1, foldase2, foldase3) and one
person as a process.
- Team up with two other groups. This gives us
three teams.
- Each team will have nine enzymes and three
people capable of conducting a process.
First Enzyme: foldase1
Second Enzyme: foldase2
Third Enzyme: foldase3
Completed Airplanes:
• MUST be IMMEDIATELY returned to foldase1
who must hold them ready for launch.
• foldase1 must hold completed airplanes on
the back of the hand between fingers.
Completed Airplanes:
• foldase1 can only hold 8 airplanes (physical
maximum)
• foldase1 may continue its job if able.
Process:
• Only ONE process per TEAM can be active at a
time unless otherwise specified (take turns).
• Process uses up completed paper airplanes by
taking a completed airplane from a Foldase1
and launching it.
• The TEAM that manufactures the most
airplanes in 4 minutes wins!
What…
• …was the substrate?
• …was the product?
• …is the name for foldase2 when it was folding
an airplane?
• …kind of inhibition occurred?
• …was an active site?
• …was an allosteric site?
• …would need to occur so that more airplanes
could be made by the foldase enzymes?
Product Feedback Inhibition
• First enzyme in a biosynthesis pathway
is(often) an allosteric enzyme
– Multiple binding sites
– Binding to effector changes conformation
Product Feedback Inhibition
Product Feedback Inhibition
Start of
pathway
X
Enzyme 1
Intermediate
Enzyme 2
Presence of product inhibits enzyme 1
Intermediate
Enzyme 3
Product
Enzymes:
1. Function
2. Inhibition
3. Product Inhibition
4. Activators
5. Cofactors
Enzymes:
1. Function
2. Inhibition
3. Product Inhibition
4. Activators
5. Cofactors
Cofactors
• Non-protein chemical required for activity of
enzymes
• Many vitamins are cofactors
– E.g., Iron, Manganese, Zinc
• Cofactor functions
– Assist with chemical reaction
• Mg2+ and Taq
– Allow protein to fold
• E.g., zinc fingers
Enzymes:
1. Function
2. Inhibition
3. Product Inhibition
4. Activators
5. Cofactors
Enzymes and Energy
Enzymes and Energy
Enzymes in Action: Luciferase
• Enzyme that oxidizes a substrate to form light
– luciferin + O2 → oxyluciferin + light
• Utilized by multiple organisms
– Fishes, fungi, copepoda, shrimps, algæ, and more
Uses of Luciferase
• Reporter genes
• Various assays
• Forensics
Video Clip
• http://www.youtube.com/watch?v=UXl8FeIoiM
– Short
• http://www.youtube.com/watch?v=9frgs8lUN
ac
– Long