Factors Affecting Enzyme Activity Class 11 Biology Notes | CBSE & NEET
Factors Affecting Enzyme Activity ( NEET Note- Explanation)
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| Factors Affecting Enzyme Activity showing the effects of temperature, pH, substrate concentration, Vmax, and competitive inhibition for CBSE Class 11 and NEET Biology. |
-Dr.Sanjaykumar Pawar
What are Factors Affecting Enzyme Activity?
Definition: Factors affecting enzyme activity are the conditions that can increase or decrease the speed of enzyme-catalysed reactions.
Main Factors
- Temperature 🌡️
- pH
- Substrate Concentration
- Inhibitors (Specific Chemicals)
NEET Tip: Remember these four factors as "TPSI"
- T = Temperature
- P = pH
- S = Substrate concentration
- I = Inhibitors
Line-by-Line Explanation
Line 1
"The activity of an enzyme can be affected by a change in the conditions which can alter the tertiary structure of the protein."
Easy Meaning
- Enzymes are proteins.
- Proteins have a special 3D (tertiary) structure.
- If this shape changes, the enzyme cannot work properly.
NEET Point
👉 Shape determines function.
If the shape changes, the active site also changes.
Line 2
"These include temperature, pH, change in substrate concentration or binding of specific chemicals that regulate its activity."
Easy Meaning
Four important factors affect enzyme activity:
- Temperature
- pH
- Substrate concentration
- Inhibitors (chemicals)
These factors either increase or decrease enzyme activity.
1. Temperature
Line
"Enzymes generally function in a narrow range of temperature."
Easy Meaning
- Every enzyme works only within a small temperature range.
- Too low or too high temperature reduces enzyme activity.
Line
"Each enzyme shows its highest activity at a particular temperature called the optimum temperature."
Easy Meaning
- Every enzyme has one best temperature.
- At this temperature, enzyme activity is maximum.
Definition
Optimum Temperature = The temperature at which an enzyme works fastest.
Line
"Activity declines both below and above the optimum value."
Easy Meaning
- If temperature becomes lower than optimum → enzyme works slowly.
- If temperature becomes higher than optimum → enzyme activity also decreases.
Line
"Low temperature preserves the enzyme in a temporarily inactive state."
Easy Meaning
- Cold temperature does not destroy enzymes.
- It only slows down enzyme activity.
- When the temperature becomes normal again, the enzyme starts working.
NEET Point
Low temperature = Reversible inactivation
Line
"High temperature destroys enzymatic activity because proteins are denatured by heat."
Easy Meaning
- High temperature changes the enzyme's shape permanently.
- This process is called denaturation.
- A denatured enzyme cannot function.
Definition
Denaturation = Permanent loss of the natural structure of a protein due to high temperature or extreme pH.
NEET Point
High temperature = Irreversible denaturation
2. pH
Line
"Enzymes generally function in a narrow range of pH."
Easy Meaning
- Every enzyme has one best pH.
- Very acidic or very basic conditions reduce enzyme activity.
Line
"Each enzyme shows highest activity at a particular pH called optimum pH."
Easy Meaning
- Each enzyme works best at a specific pH.
Examples (NEET)
- Pepsin → pH 2 (acidic)
- Trypsin → pH 8 (alkaline)
- Salivary amylase → pH 6.8–7 (nearly neutral)
Line
"Activity declines below and above optimum pH."
Easy Meaning
- Too much acid or too much base changes the enzyme's shape.
- Therefore, enzyme activity decreases.
3. Substrate Concentration
Line
"With the increase in substrate concentration, the velocity of the enzymatic reaction rises at first."
Easy Meaning
- More substrate means more collisions with enzymes.
- Therefore, the reaction becomes faster initially.
Line
"The reaction ultimately reaches a maximum velocity (Vmax)."
Easy Meaning
- After some time, the reaction reaches its highest possible speed.
- This maximum speed is called Vmax.
Definition
Vmax = Maximum rate of an enzyme-catalysed reaction.
Line
"Vmax is not exceeded by any further rise in substrate concentration."
Easy Meaning
- Adding more substrate after Vmax does not increase the reaction rate.
- The enzyme is already working at full capacity.
Line
"This is because enzyme molecules are fewer than substrate molecules."
Easy Meaning
- There are only a limited number of enzyme molecules.
- Extra substrate has no free enzyme to bind with.
Line
"After saturation of enzyme molecules, there are no free enzyme molecules to bind with additional substrate molecules."
Easy Meaning
- Every active site becomes occupied.
- This condition is called enzyme saturation.
Definition
Enzyme Saturation = All active sites of enzymes are occupied by substrate molecules.
4. Inhibitors
Line
"The activity of an enzyme is sensitive to specific chemicals."
Easy Meaning
Some chemicals reduce or stop enzyme activity.
These chemicals are called inhibitors.
Line
"When the binding of the chemical shuts off enzyme activity, the process is called inhibition."
Easy Meaning
- If a chemical binds to an enzyme and stops it from working, the process is called inhibition.
Definition
Inhibition = Decrease or stoppage of enzyme activity due to an inhibitor.
Line
"The chemical is called an inhibitor."
Easy Meaning
An inhibitor is a chemical that decreases enzyme activity.
Competitive Inhibitor
Line
"When the inhibitor closely resembles the substrate in molecular structure."
Easy Meaning
- The inhibitor looks almost like the real substrate.
- Therefore, the enzyme cannot distinguish between them.
Line
"It inhibits enzyme activity and is called a competitive inhibitor."
Easy Meaning
- The inhibitor competes with the substrate for the active site.
- This is called competitive inhibition.
Definition
Competitive Inhibitor = A molecule that resembles the substrate and competes for the enzyme's active site.
Line
"The inhibitor competes with the substrate for the substrate-binding site."
Easy Meaning
- Both the substrate and inhibitor try to bind to the same active site.
- Only one can bind at a time.
Line
"The substrate cannot bind and enzyme action declines."
Easy Meaning
- If the inhibitor binds first, the substrate cannot enter.
- Therefore, product formation decreases.
Line
"Example: inhibition of succinic dehydrogenase by malonate."
Easy Meaning
- Enzyme: Succinic dehydrogenase
- Substrate: Succinate
- Inhibitor: Malonate
Malonate resembles succinate and blocks the enzyme's active site.
NEET Example
Succinic dehydrogenase + Succinate → Normal reaction
Succinic dehydrogenase + Malonate → Reaction blocked
Line
"Competitive inhibitors are often used in the control of bacterial pathogens."
Easy Meaning
Some medicines work as competitive inhibitors.
They block important bacterial enzymes, stopping bacterial growth and helping to treat infections.
Graph-Based Concepts (Figure 9.5)
A. Effect of pH
- Enzyme activity increases up to the optimum pH.
- After the optimum pH, activity decreases.
B. Effect of Temperature
- Activity increases with temperature up to the optimum temperature.
- Beyond this point, activity falls sharply because of denaturation.
C. Effect of Substrate Concentration
- Reaction rate increases as substrate concentration increases.
- Eventually, it reaches Vmax, where all enzyme active sites are occupied.
- Adding more substrate does not increase the reaction rate further.
Flow Chart
Factors Affecting Enzyme Activity ↓
- Temperature 🌡️
- pH 🧪
- Substrate Concentration 🧬
- Inhibitors 🚫
NEET Important Points
- Enzymes work best at an optimum temperature and optimum pH.
- Low temperature causes temporary (reversible) inactivation.
- High temperature causes permanent denaturation.
- Increasing substrate concentration increases reaction rate only until Vmax is reached.
- Vmax is the maximum reaction velocity.
- At enzyme saturation, all active sites are occupied.
- An inhibitor decreases enzyme activity.
- A competitive inhibitor resembles the substrate and competes for the active site.
- Example: Malonate competitively inhibits succinic dehydrogenase by resembling succinate.
- Competitive inhibitors are used in controlling bacterial pathogens.
One-Line Revision (Exam Ready)
- Optimum temperature = Temperature at which enzyme activity is highest.
- Optimum pH = pH at which enzyme activity is highest.
- Low temperature = Temporary inactivation (reversible).
- High temperature = Denaturation (irreversible).
- Vmax = Maximum rate of an enzyme-catalysed reaction.
- Enzyme saturation = All active sites are occupied.
- Inhibition = Decrease in enzyme activity due to an inhibitor.
- Competitive inhibitor = Molecule that resembles the substrate and competes for the active site.
- Example: Malonate inhibits succinic dehydrogenase.
- Applications: Competitive inhibitors are used to control bacterial pathogens.
NEET Mnemonic
"TPSI"
- T = Temperature
- P = pH
- S = Substrate concentration
- I = Inhibitors
CBSE Class 11 Biology Question Bank
Chapter: Biomolecules
Topic: Factors Affecting Enzyme Activity
A. Multiple Choice Questions (MCQs)
1. Which of the following is not a factor affecting enzyme activity?
a) Temperature
b) pH
c) Substrate concentration
d) Light intensity
Answer: d) Light intensity
2. The temperature at which an enzyme shows maximum activity is called:
a) Critical temperature
b) Optimum temperature
c) Maximum temperature
d) Normal temperature
Answer: b) Optimum temperature
3. High temperature reduces enzyme activity because:
a) Enzymes evaporate b) Proteins are denatured c) Substrate is destroyed d) Water is removed
Answer: b) Proteins are denatured
4. At low temperature, enzymes become:
a) Permanently inactive b) Temporarily inactive c) Destroyed d) Denatured
Answer: b) Temporarily inactive
5. Every enzyme has a specific:
a) Colour b) Optimum pH c) Density d) Shape only
Answer: b) Optimum pH
6. The maximum velocity of an enzyme reaction is represented by:
a) Km b) Vmax c) ATP d) ES
Answer: b) Vmax
7. Vmax is achieved when:
a) Enzyme molecules are destroyed b) All enzyme active sites are occupied c) Temperature is low d) pH becomes acidic
Answer: b) All enzyme active sites are occupied
8. A competitive inhibitor:
a) Binds to the product b) Resembles the substrate c) Increases enzyme activity d) Destroys the enzyme
Answer: b) Resembles the substrate
9. Malonate is a competitive inhibitor of:
a) Pepsin b) Amylase c) Succinic dehydrogenase d) Trypsin
Answer: c) Succinic dehydrogenase
10. Which factor changes the tertiary structure of enzymes?
a) Temperature b) pH c) Inhibitors d) All of these
Answer: d) All of these
B. Very Short Answer Questions (1 Mark)
Q1. What is the optimum temperature?
Answer: The temperature at which an enzyme shows maximum activity.
Q2. What is the optimum pH?
Answer: The pH at which an enzyme works most efficiently.
Q3. What is Vmax?
Answer: The maximum rate of an enzyme-catalysed reaction.
Q4. Define denaturation.
Answer: Denaturation is the permanent loss of the natural structure and activity of a protein due to high temperature or extreme pH.
Q5. What is an inhibitor?
Answer: An inhibitor is a chemical that decreases or stops enzyme activity.
Q6. Name the type of inhibitor that resembles the substrate.
Answer: Competitive inhibitor.
Q7. What happens to enzyme activity at low temperature?
Answer: It becomes temporarily inactive.
Q8. Name one competitive inhibitor.
Answer: Malonate.
C. Short Answer Questions (2 Marks)
Q1. State any two factors affecting enzyme activity.
Answer:
- Temperature
- pH
Q2. Why does enzyme activity decrease at high temperature?
Answer: High temperature denatures the protein, changing the shape of the active site and reducing enzyme activity.
Q3. Why does enzyme activity stop increasing after Vmax?
Answer: Because all active sites of the enzyme become occupied by substrate molecules (enzyme saturation).
Q4. What is competitive inhibition?
Answer: Competitive inhibition occurs when an inhibitor resembles the substrate and competes for the enzyme's active site, reducing enzyme activity.
D. Short Answer Questions (3 Marks)
Q1. Explain the effect of temperature on enzyme activity.
Answer:
- Enzyme activity increases with temperature up to the optimum temperature.
- At low temperatures, enzymes become temporarily inactive.
- At temperatures above the optimum, enzymes are denatured and lose activity permanently.
Q2. Explain the effect of substrate concentration on enzyme activity.
Answer:
- As substrate concentration increases, the reaction rate increases.
- Eventually, all enzyme active sites become occupied.
- The reaction reaches Vmax, and adding more substrate does not increase the reaction rate.
Q3. Explain competitive inhibition with an example.
Answer: A competitive inhibitor resembles the substrate and competes for the enzyme's active site. This prevents the substrate from binding, reducing enzyme activity. For example, malonate inhibits succinic dehydrogenase.
E. Long Answer Questions (5 Marks)
Q1. Explain the factors affecting enzyme activity.
Answer:
The main factors affecting enzyme activity are:
1. Temperature
- Enzymes work best at an optimum temperature.
- Low temperature causes temporary inactivation.
- High temperature causes denaturation.
2. pH
- Every enzyme has an optimum pH.
- Enzyme activity decreases if the pH is too high or too low.
3. Substrate Concentration
- Increasing substrate concentration increases reaction rate.
- The reaction reaches Vmax when all active sites are occupied.
4. Inhibitors
- Inhibitors decrease enzyme activity.
- Competitive inhibitors resemble the substrate and compete for the active site.
Q2. Describe competitive inhibition with a suitable example.
Answer: Competitive inhibition occurs when an inhibitor has a structure similar to the substrate. The inhibitor competes with the substrate for the enzyme's active site. As a result, fewer substrate molecules bind to the enzyme, reducing the reaction rate.
Example: Malonate competes with succinate for the active site of succinic dehydrogenase.
F. Assertion and Reason Questions
Q1.
Assertion (A): Enzymes show maximum activity at the optimum temperature.
Reason (R): Every enzyme functions best at a specific temperature.
Answer: Both A and R are true, and R is the correct explanation of A.
Q2.
Assertion (A): High temperature permanently destroys enzyme activity.
Reason (R): Heat causes protein denaturation.
Answer: Both A and R are true, and R is the correct explanation of A.
Q3.
Assertion (A): Increasing substrate concentration always increases enzyme activity.
Reason (R): Enzyme saturation occurs at Vmax.
Answer: Assertion is false, but Reason is true.
Q4.
Assertion (A): Competitive inhibitors bind to the enzyme's active site.
Reason (R): They resemble the substrate in structure.
Answer: Both A and R are true, and R is the correct explanation of A.
G. Fill in the Blanks
-
Enzymes show maximum activity at the __________ temperature.
Answer: optimum -
High temperature causes protein __________.
Answer: denaturation -
The maximum velocity of an enzyme reaction is called __________.
Answer: Vmax -
The chemical that reduces enzyme activity is called an __________.
Answer: inhibitor -
A competitive inhibitor resembles the __________.
Answer: substrate -
Low temperature causes __________ inactivation of enzymes.
Answer: temporary -
Malonate inhibits the enzyme __________.
Answer: succinic dehydrogenase -
The enzyme's three-dimensional structure is called its __________ structure.
Answer: tertiary
H. Case Study Questions
Case Study
A student performed an experiment to study enzyme activity. The enzyme showed maximum activity at 37°C and pH 7. When the temperature was increased to 80°C, the enzyme stopped working. Increasing substrate concentration increased the reaction rate only up to a certain point. Later, adding malonate reduced enzyme activity.
Questions
1. What is 37°C called for this enzyme?
Answer: Optimum temperature.
2. Why did the enzyme stop working at 80°C?
Answer: Because the enzyme was denatured by high temperature.
3. Why did the reaction rate stop increasing after some time?
Answer: All enzyme active sites became occupied, and Vmax was reached.
4. What type of inhibitor is malonate?
Answer: Competitive inhibitor.
5. Which enzyme is inhibited by malonate?
Answer: Succinic dehydrogenase.
I. Statement-Based Questions
State whether the following statements are True or False.
-
Every enzyme has an optimum temperature.
Answer: True -
High temperature permanently denatures enzymes.
Answer: True -
Low temperature permanently destroys enzymes.
Answer: False -
Enzyme activity always increases with increasing substrate concentration.
Answer: False -
Competitive inhibitors resemble the substrate.
Answer: True -
Vmax is reached when all active sites are occupied.
Answer: True -
Malonate is a competitive inhibitor.
Answer: True -
Enzymes work over a wide range of pH values with equal efficiency.
Answer: False
J. Match the Following
| Column A | Column B |
|---|---|
| A. Optimum temperature | 1. Maximum reaction rate |
| B. Vmax | 2. Best temperature for enzyme activity |
| C. Competitive inhibitor | 3. Resembles the substrate |
| D. Denaturation | 4. Permanent loss of enzyme activity |
| E. Malonate | 5. Inhibits succinic dehydrogenase |
Answers
- A → 2
- B → 1
- C → 3
- D → 4
- E → 5
K. Competency-Based Questions
Q1. During an experiment, a student noticed that increasing substrate concentration beyond a certain limit did not increase the reaction rate. Explain the reason.
Answer: The reaction had reached Vmax, where all enzyme active sites were occupied by substrate molecules. As no free active sites were available, adding more substrate could not increase the reaction rate.
Q2. A food-processing company stores enzymes at low temperatures instead of high temperatures. Give a scientific reason.
Answer: Low temperatures keep enzymes temporarily inactive without damaging them, preserving their activity. High temperatures can denature enzymes permanently and make them non-functional.
L. Diagram-Based Question
Q. Draw and explain the graph showing the effect of substrate concentration on enzyme activity.
Answer:
- The reaction rate increases with increasing substrate concentration.
- It finally reaches Vmax, where all enzyme active sites are saturated.
- Beyond Vmax, increasing substrate concentration does not increase the reaction rate.
Quick CBSE Revision Points
- Enzyme activity depends on temperature, pH, substrate concentration, and inhibitors.
- Every enzyme has an optimum temperature and optimum pH.
- Low temperature causes temporary inactivation; high temperature causes permanent denaturation.
- Vmax is the maximum reaction rate when all active sites are occupied.
- Competitive inhibitors resemble the substrate and compete for the active site.
- Example: Malonate is a competitive inhibitor of succinic dehydrogenase.
- Competitive inhibitors can be used to control bacterial pathogens.
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