Download FACTORS AFFECTING ENZYME ACTION

2: Enzyme Action
Lesson Objectives:
•
•
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Why are enzymes and their structure important. (AO1: D)
Use the pictures to describe the lock and key and induced fit model of enzymes (AO2: C)
Use your knowledge of enzymes to explain the effect of changing conditions on the
enzyme action (AO2 and AO3: A)
Homework: Use your knowledge of enzymes to explain the following:
- Heating food before being canned
- Foods preserved in vinegar
Keywords: substrate, enzyme, enzyme-substrate complex, active site,
complementary
EXAM TIP: When answering questions on enzymes, always use the words
‘enzyme-substrate complex’ and ‘active site’, worth 1 mark. 
Quick recap of proteins.
1) Primary structure = long chain of amino
acids forming a polypeptide.
2) Secondary structure = hydrogen bonds
between O in carboxyl and H in amino ground
cause helix or corrugated shape to form.
3) Tertiary = ionic, more hydrogen or
disulphide bonds cause FOLDING into 3d
shape (allowing it to do a job).
4) Quaternary = more than one peptide bond
together and/or a prosthetic group (non
peptide).
Enzymes are tertiary or quaternary (globular) proteins.
What do enzymes do?
Sucrose + water  glucose + fructose.
• The above is a simple reaction that happens in nature.
• For the reaction to happen, some energy needs to be put in to
start it off. The ACTIVATION ENERGY.
• If left to work on its own in a human body or plant etc. not many
reactions would have enough energy to start in the cool
temperatures inside living organisms and the reactions would be
too slow.
• Enzymes make the activation energy lower and thus make
reactions happen much faster.
Activation energy.
The red line is how much
energy would be needed to
get the reaction started on
its own (no enzymes).
The enzyme reduces the
activation energy to the
green line. The lower energy
allows the reaction to
happen inside the
body/organism at a lower
temperature and at a faster
rate. HOW USEFUL!
Tip – without enzymes we
would not be able to
function properly.
Enzyme Structure
AO1
• 3-D structure - the amino acid sequence causes bonds to form and
the polypeptide to fold into a 3D shape.
• The 3D shape causes the enzyme to form an active site - this is a
“hole” that forms and is able to bind onto other molecules by
forming temporary bonds between them.
• The molecule that the enzyme binds to is called a substrate.
• When the enzyme binds to the substrate it is called an enzymesubstrate complex.
The two enzyme
models.
1) Lock and Key
2) Induced fit.
Enzyme Action
AO2
Earliest model - LOCK AND KEY MODEL
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•
•
Enzymes have rigid and set active site shapes.
These bind specifically to the substrate.
MODEL LIMITATION – scientists noticed other molecules binding to the enzyme
causing it to change shape and activity of the enzyme. This lead to the idea of the
second model (induced fit)
•
Each enzyme only catalyses one type of substrate, this means that enzymes are
s___________________ .
Explain why changing one of the amino acid group can prevent the enzyme from
working? (Think bonds and folding)(AO2: B)
•
Enzyme Action
AO2
Current model INDUCED FIT MODEL
•
This is slightly different to the previous model.
•
INITIALLY the enzyme active site and the substrate are NOT COMPLIMENTARY in shape.
•
When an enzyme and substrate come close to each other they interact.
•
This interaction causes the active site to change shape and become a COMPLIMENTARY and
FUNCTIONAL active site. An INDUCED FIT. (ie. The enzyme is flexible and moulds itself around
the substrate).
•
The enzyme binding to the substrate causes substrate bonds to bend and weaken, this is why
the activation energy gets lower.
Enzyme Action
AO1
For an enzyme to work it must:
1. Come into contact with the substrate
2. Have an active site which is complementary to
the substrate
Following factors can affect the rate of reaction:
1. Temperature
2. pH
3. Substrate concentration
4. Competitive and non-competitive inhibitors
THESE WILL BE DISCUSSED IN CLASS!
Enzyme Inhibition
AO2
COMPETITIVE INHIBITORS
• Competitor inhibitor has the same molecular shape as the
substrate, so they compete with the substrate to bind to
the active site.
• The rate of reaction depends on the concentration of the
substrate and the inhibitor.
• Substrate concentration is high then the effect of inhibitor
is reduced.
• When competitive inhibitor leave the place another
substrate molecule takes the place.
Enzyme Inhibition
AO2
NON-COMPETITIVE INHIBITOR
• Binds to the non-active site and alters the shape.
• The substrate molecule can no longer bind,
reducing the rate of reaction.