Transcript Enzyme Action: Lock and Key Model

Factors affecting enzyme action
• Summarise all work completed so far on
enzymes
• Use this knowledge to EXPLAIN the shape
of graphs and answer the questions set by
the exam board
• Suggest how the shape of a graph may be
affected when certain factors are changed
Use labelled diagrams to summarise these two
theories explaining how enzymes work and decide
which is best and why – you have 5 mins max
Lock and Key Model
Induced fit model
Enzyme Action:
Lock and Key Model
• An enzyme binds a substrate in a region called the
active site
• Only certain substrates can fit the active site
• Amino acid R groups in the active site help
substrate bind
• Enzyme-substrate complex forms
• Substrate reacts to form product
• Product is released
Lock and Key Model
P
S
+
+
S
P
E
+
S
ES complex
E +
P
Enzyme Action:
Induced Fit Model
• Enzyme structure flexible, not rigid
• Enzyme and active site adjust shape to bind
substrate
• Increases range of substrate specificity
• Shape changes also improve catalysis during
reaction
Enzyme Action:
Induced Fit Model
P
S
S
P
E
+
S
ES complex
E
+
P
White board quick fire
Draw a graph to show the effects of
increasing the concentration of
Hydrogen Peroxide on the activity of
catalase – label the axes
Factors Affecting Enzyme Action:
Substrate Concentration
• Increasing substrate concentration increases
the rate of reaction (enzyme concentration is
constant)
• Maximum activity reached when all of enzyme
combines with substrate – improve on this D
grade answer
http://www.bbc.co.uk/education/asg
uru/biology/02biologicalmolecules/
01proteins/11enzymes/03enzymes_
b/index.shtml
Substrate conc
Factors Affecting Enzyme Action
Maximum activity
Reaction
Rate
substrate concentration
White board quick fire
Draw a graph to show the effects of
increasing the temperature on the
activity of catalase – label the axes
Factors Affecting Enzyme Action:
Temperature
• Little activity at low temperature but rate
increases with temperature
• Most active at optimum temperatures (usually
37°C in humans) nb have you read the article about
thermophilic and psychrophilic enzymes?
• Denaturation occurs at high temperatures (nb
some enzymes are active at
• 115oC)
Factors Affecting Enzyme Action
Optimum temperature
Reaction
Rate
Why is this graph
NOT correct?
Low
High
Temperature
http://www.bbc.co.uk/education/asg
uru/biology/02biologicalmolecules/
01proteins/11enzymes/03enzymes_
b/index.shtml
On a white board
Redraw the line showing the effects
of substrate concentration at 25oC
Now add a second line to your graph
to show the effects of increasing the
temperature by 10oC
White board quick fire
Draw a graph to show the effects of
increasing the pH of on the activity of
amylase – label the axes
Factors Affecting Enzyme Action:
pH
•
•
•
•
•
Maximum activity at optimum pH
R groups of amino acids have proper charge
Tertiary structure of enzyme is correct
Narrow range of activity
Most lose activity in low or high pH – WHY?
Factors Affecting Enzyme Action
Reaction
Rate
Optimum pH
3
5
7 9 11
pH
White board quick fire
Draw a graph to show the effects of
increasing the concentration of an
enzyme on the rate of products being
formed – label the axes
Sucrase activity Q
Sucrase has an optimum temperature of
37°C and an optimum pH of 6.2. Determine
the effect of the following on its rate of
reaction
(1) no change (2) increase (3) decrease
A. Increasing the concentration of sucrose
B. Changing the pH to 4
C. Running the reaction at 70°C
Solution
Sucrase has an optimum temperature of 37°C and
an optimum pH of 6.2. Determine the effect of the
following on its rate of reaction
(1) no change (2) increase (3) decrease
A. 2, 1 Increasing the concentration of sucrose
B. 3 Changing the pH to 4
C. 3 Running the reaction at 70°C