Proteins Making Chemical Reactions Possible
Energy and chemical reactions
 Most chemical reactions require energy to begin
- the energy required to start a chemical reaction is
called activation energy.
What are enzymes?
 Enzymes are proteins which reduce activation energy
allowing chemical reactions to occur in living things
Enzymes reduce activation energy
Enzymes Act as Biological Catalysts
 Catalysts are inorganic molecules that speed up chemical
reactions
- catalysts remain unchanged by the reaction that they
speed up.
-one molecule of catalyst can catalyze (start) many
chemical reactions
 Enzymes speed up reactions in living things
-enzymes are not changed by the reaction they speed up
- one molecule of enzyme can catalyze (start) many
reactions
Active Site
 Enzymes have an area called an active site.
- the active site is where the chemical reaction occurs
The Shape of the Enzyme Determines
Function
 The active site of the enzyme fits with only one type of
molecule known as the substrate.
 Substrate is the molecule that the enzyme acts on.
 The fact that the active site can only accept one type of
substrate is known as enzyme specificity
Enzyme Reactions
 Written as :
Enzyme + Substrate
ES
Enzyme + Product
- ES refers to the enzyme substrate complex,
time when the substrate joins with
the active site.
the
Example
Catalase + 2H2O2
enzyme
substrate
ES
enzyme
substrate
complex
Catalase + 2H2O + O2
enzyme
product product
Two Ideas About Enzyme
Action
Lock & Key Model
Induced Fit Model
Lock & Key Model
 Substrate fits into the active site like a key into a lock
 The enzyme puts stress on the
bond which reduces the amount
of energy needed to break apart
the substrate
 The products of the reaction
leave and make the enzyme
available for more substrate
Induced Fit Model
 Substrate doesn’t quite
fit into the active site
 Substrate causes
(induces) the enzyme to
change shape – allows
the substrate to fit into
the active site
 Enzyme stresses bonds
on substrate
Enzymes can build molecules
Substrate molecules can only bond
one way.
Substrate molecules
fit into the active
site in the best
position to bond
Once in the active site,
the molecules of substrate join
Enzyme Inhibitors
 Inhibitors control the rate of enzyme activity
- if there is too much of an enzyme’s product,
inhibitors can slow or even stop an enzyme’s activity
 Two types of Inhibition
- Competitive
- Non Competitive
Competitive Inhibition
 The inhibitor is a molecule that can occupy part of the
active site
 While the inhibitor is in the active site, substrate can’t
bind with the enzyme – inhibitors compete with the
substrate for the active site
inhibitor competes with substrate
inhibitor blocks the active site
Noncompetitive Inhibition
 The inhibitor binds with the enzyme at a site away from the
active site.
 Inhibitor causes enzyme to change shape – prevents
substrate from entering the active site
Inhibitor binds with enzyme
Enzyme changes shape keeps
substrate from active site
Feedback Inhibition
 Enzymes are often part of a
series of reactions called a
biochemical pathway
- the product of one enzyme
acts as the substrate for
another enzyme
-the final product – acts as an
inhibitor for the first enzyme
in the pathway
- this stops the pathway and
the production of the endproduct stops as well
Feedback Inhibition
The end-product of the
pathway is used for other
purposes
As the end-product is
used, its concentration
drops
When the concentration
of the end-product drops
to a low level, inhibition ends
and the enzyme pathway
resumes operation
Co-Enzymes and Co-factors
 Co-enzymes and Co-factors are molecules that help
certain enzymes to catalyze a reaction
- co-enzymes and co-factors often act as carriers of
electrons, atoms or functional groups needed to
complete a reaction.
Co-Enzymes and Co-Factors
- while they bind to an enzyme’s active site, and
participate in the reaction, they are not changed by the
reaction and aren’t considered substrates.
- Co-enzymes are organic molecules and include: NAD,
NADP, FAD, vitamin B 1, vitamin B 6, and vitamin B 12
- Co-factors are inorganic molecules and include
dietary minerals like zinc, iron, copper & potassium
Denatured Enzymes
• Enzymes are proteins and if they are exposed to
extremes of temp or pH lose their shape
- if a protein loses its shape, it loses its function
- a protein that loses its shape is said to be denatured
- if an enzyme is denatured, substrate can’t enter the
active site
extreme
temp
or
pH
Common Enzymes
 Amylase - breaks down starch
 Catalase – breaks down H2O2
 DNA polymerase – joins DNA nucleotides to build
DNA
 Lipase – break apart fats
 Lactase – breaks apart lactose – milk sugar
 Protease- breaks apart protein molecules
-What does –ase in a molecules’ name imply?
Vocabulary for Enzyme Excitement
 Enzyme
 Activation energy
 Catalyst
 Active site
 Substrate
 Enzyme specificity
 Lock & Key Model
 Induced Fit Model
 Enzyme inhibitor
Competitive Inhibition
Non Competitive Inhibition
Denatured Protein
Feedback Inhibition
Biochemical Pathway
co-enzyme/co-factor