Topic 4: Chapter 5
Enzymes Enzymes – – Part 3Part 3
Limiting Limiting
FactorsFactors
What is a limiting factor?
Any factor that directly affects the rate of reaction at which a process occurs if its quantity is changed
The value of this factor has to be increased in order to increase the rate of the process
Factors affecting enzyme activity
1) Temperature2) pH3) Substrate
Concentration4) Enzyme
Concentration
Example 1 Point X
Example 1• Independent Variable: Substrate concentration
• LIMITING FACTOR IS Substrate concentration
From 0 to Point XFrom 0 to Point X
Description Explanation
As the [substrate] increases, the rate of reaction increases until Point X when rate of reaction reaches its maximum.
At any [substrate] before Point X, there are more enzyme molecules than substrate molecules
At Point X, all the enzyme active sites are occupied by substrate molecules
Example 1• Independent Variable: Substrate concentration
• LIMITING FACTOR IS Enzyme concentration
Beyond Point XBeyond Point X
Description Explanation
Graph remains constant / becomes a plateau after Point X.
Maximum rate of reaction
After point X, the rate of reaction does not increase even when [substrate] increases.
This is because all the enzyme molecule’s active sites are being occupied at any one time. That is, all the enzyme molecules are saturated.
Amount of products formed per unit time remains constant
Example 2
0.4moldm-3 Enzyme
0.2moldm-3 Enzyme
Rat
e o
f R
eact
ion
Substrate Concentration / Arbitrary Units
(A)
(B)
X Y
Example 2• Independent Variable: Substrate concentration
From 0 to Point YFrom 0 to Point Y
Description Explanation
Rate of reaction increases as [Substrate] increases for both Graphs A and B.
At any [Substrate] before Point Y, there are more enzymes than substrate molecules.
At Point X, all the enzyme active sites are occupied by substrate molecules
Rate of reaction of (B) is double that of (A)
There are double the number of enzyme molecules in (B). Double the frequency of collision between Enzyme and Substrate molecules in (B)
LIMITING FACTOR Substrate Concentration
Example 2• Independent Variable: Enzyme concentration
Beyond Point YBeyond Point Y
LIMITING FACTOR Enzyme Concentration
Description Explanation
Graph remains constant / becomes a plateau after Point X.
Maximum rate of reaction
After point X, the rate of reaction does not increase even when [substrate] increases.
This is because all the enzyme molecule’s active sites are being occupied at any one time. That is, all the enzyme molecules are saturated.
Amount of products formed per unit time remains constant
Rate of reaction of (B) is double that of (A)
Double the number of enzyme molecules in (B). Double the number of E-S complex formed per unit time. Therefore, double the amount of products formed
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