Enzymes
Giving cells control �of all their chemical reactions
Counter Top
Outside
Human Body
Counter Top
Outside
Human Body
Counter Top
Outside
Human Body
in days / weeks
in months / years
in hours
partially decomposed
(mouldy)
fully decomposed�(compost)
broken down into smaller nutrients and absorbed into blood
Counter Top
Outside
Human Body
in days / weeks
in months / years
in hours
partially decomposed
(mouldy)
fully decomposed�(compost)
broken down into smaller nutrients and absorbed into blood
WHY THE DIFFERENCE?
Why The Difference?
Why The Difference?
Enzymes are highly specialized molecular tools that make extremely specific chemical reactions take place as a result of their 3D shape
The Progress of a Chemical Reaction
Progress of Reaction / Time
Energy
Reactant(s)
Product(s)
matter tends to lose energy and remain in its lowest stable energy state.
Why does this exist in nature
?
AB
A
B
The Progress of a Chemical Reaction
Progress of Reaction / Time
Energy
Reactant(s)
Product(s)
AB
EA
To make or break bonds requires some energy INPUT.
This is called
ACTIVATION ENERGY (EA )
A
B
The Progress of a Chemical Reaction
Progress of Reaction / Time
Energy
Reactant(s)
Product(s)
AB
EA
All reactions require activation energy to proceed. Even the endothermic reaction shown below
A
B
The Progress of a Chemical Reaction
Progress of Reaction / Time
Energy
Reactant(s)
Product(s)
AB
The Progress of a Chemical Reaction
Progress of Reaction / Time
Energy
Reactant(s)
Product(s)
AB
The Progress of a Chemical Reaction
Progress of Reaction / Time
Energy
Reactant(s)
Product(s)
AB
The Progress of a Chemical Reaction
Progress of Reaction / Time
Energy
Reactant(s)
Product(s)
AB
A
B
Transition State
The Progress of a Chemical Reaction
Progress of Reaction / Time
Energy
Reactant(s)
Product(s)
AB
A
B
The Progress of a Chemical Reaction�WITH AN ENZYME
Progress of Reaction / Time
Energy
Reactant(s)
Product(s)
AB
The Progress of a Chemical Reaction�WITH AN ENZYME
Progress of Reaction / Time
Energy
Reactant(s)
Product(s)
AB
EA
The presence of an enzyme �LOWERS THE ACTIVATION ENERGY required for the reaction to proceed
The Progress of a Chemical Reaction�WITH AN ENZYME
Progress of Reaction / Time
Energy
Reactant(s)
Product(s)
AB
no enzyme
with enzyme
The Progress of a Chemical Reaction�WITH AN ENZYME
Progress of Reaction / Time
Energy
Reactant(s)
Product(s)
AB
A
B
The Progress of a Chemical Reaction�WITHOUT AN ENZYME
Progress of Reaction / Time
Energy
Reactant(s)
Product(s)
ambient energy at body temperature
AB
No reaction
The Progress of a Chemical Reaction�WITH AN ENZYME
Progress of Reaction / Time
Energy
Reactant(s)
Product(s)
AB
A
B
ambient energy at body temperature
Reaction is spontaneous and goes to completion
The Progress of a Chemical Reaction�WITH AN ENZYME
Progress of Reaction / Time
Energy
Reactant(s)
Product(s)
AB
A
B
… but HOW does an enzyme lower the activation energy?
Important Terminology
A
B
A
B
Reactants
Products
Enzyme(s)
Substrates
Important Terminology
A
B
Reactants
Substrates
Enzyme
amino acid
protein
a protein that facilitates �a chemical reaction
Important Terminology
A
B
A
B
Enzyme
a protein that facilitates �a chemical reaction
Important Terminology
A
B
Enzyme-Substrate Complex
the location on the enzyme where the substrate binds
active site
The Induced Fit Model
A
B
The 3D conformational change of the enzyme-substrate complex is what causes a reaction to occur.
A
B
Enzyme-Substrate Complex
The Induced Fit Model
The Induced Fit Model
3D Shape
A
B
Notice that when the ES complex forms, �the 3D shape of the active site orients the substrate(s) in a very specific arrangement
forms ONLY this specific bond
A
B
3D Shape
A
B
This can encourage the �formation of a specific new bond.
forms ONLY this specific bond
3D Shape
A
B
The 3D conformational change can �stress existing bonds and break them.
A
B
R-Groups in the Active Site
Product
Substrate
The R-groups of the amino acids in the active site can interact with the substrate in ways that encourage or weaken chemical bonds.
R-Groups in the Active Site
Though R-groups can be involved in the reaction, �they are not chemically altered.
Summary: How Does an Enzyme Lower Activation Energy?
AB
Progress of Reaction / Time
Energy
Reactant(s)
Product(s)
no enzyme
with enzyme
A
B
Enzymes are REUSABLE�(i.e. not used up in the reaction)
A
B
Product(s) have new chemical and physical properties and a new 3D shape, so they no longer bind to the active site.�When product(s) exit, the enzyme returns to its original conformation and can be reused
Enzyme Cycle
Summary: What Do Enzymes Do?
Lower activation energy (EA)
Summary: What Do Enzymes Do?
Make reactions spontaneous.
(i.e. make reactions possible that otherwise would not happen)
Summary: What Do Enzymes Do?
Make reactions highly specific
A
B
A
B
Enzyme
NOT….
A
B
A
B
A
A
A
A
B
A
B
Summary: What Do Enzymes Do?
Make reactions occur rapidly and to completion�since enzyme molecules are reusable
Loss of Enzyme Activity�(denaturation)
Primarily through the disruption of hydrogen bonds, complete or partial unfolding of an enzyme alters the 3D shape of the active site.
Loss of Enzyme Activity�(denaturation)
low kinetic energy
enzyme rigidity
Temperature
Enzyme Activity
(reaction rate)
denaturation
optimum
Loss of Enzyme Activity�(denaturation)
denaturation
pH
Enzyme Activity
(reaction rate)
denaturation
optimum
acidic
basic
Loss of Enzyme Activity�(denaturation)
pH
Enzyme Activity
(reaction rate)
denaturation
optimum
acidic
basic
denaturation
more sensitive to acid
Loss of Enzyme Activity�(denaturation)
denaturation
pH
Enzyme Activity
(reaction rate)
optimum
acidic
basic
denaturation
more sensitive to base
Enzyme Inhibition and Activation
Some enzymes can be�turned on and off
Competitive Inhibition
i
i
A
B
A molecule other than the substrate binds or partially binds to the active site. This blocks access to the active site for any other molecule.
competitive inhibitor
Competitive Inhibition
i
i
A
B
The presence of the competitive inhibitor �turns the enzyme OFF.
competitive inhibitor
Non-Competitive Inhibition
active site
allosteric site
Non-Competitive Inhibition
A
B
A
B
When nothing is bound to the allosteric site, the active site is receptive to substrate. The enzyme is ON.
* induced fit not shown for simplicity
Non-Competitive Inhibition
i
i
non-competitive (allosteric) inhibitor
If a molecule binds to the allosteric site �the enzyme will change its 3D shape.
Non-Competitive Inhibition
i
A
B
When a non-competitive inhibitor is bound to the allosteric site, the active site is no longer receptive to substrate. �The enzyme is OFF.
Enzyme Activation
A
B
For some enzymes the allosteric site �can be used to turn it ON.
Enzyme Activation
a
a
When an activator is bound to the allosteric site, the enzyme becomes receptive to the enzyme.
activator
Enzyme Activation
a
The enzyme is only ON when the activator is bound.
A
B
A
B
Enzyme Activation
When a coenzyme binds to the active site it turns the enzyme on by giving it the correct 3D shape
apoenzyme
holoenzyme
coenzyme
Enzyme Activation
If the activator molecule bound to the active site �is not made of protein it is called a cofactor.
holoenzyme
cofactor
Summary of Inhibition
ON
OFF
competitive
non-competitive
i
i
i
Summary of Activation
ON
OFF
allosteric
Cofactors / coenzymes
a
THE END
(or is it just the beginning)